CARBON ISOTOPES (δ13C & Δ14C) AND TRACE ELEMENTS (Ba, Mn, Y) IN
SMALL MOUNTAINOUS RIVERS AND COASTAL CORAL SKELETONS IN
PUERTO RICO
DISSERTATION
Presented in Partial Fulfillment of the Requirements for
the degree of Doctor of Philosophy in the Graduate
School of The Ohio State University
By
Ryan Patrick Moyer, M.S.
*****
The Ohio State University
2008
Dissertation Committee:
Approved by:
Professor Andréa G. Grottoli, Advisor
Professor James E. Bauer
Professor Anne E. Carey
Professor Yu-Ping Chin
Professor Matthew R. Saltzman
________________________________
Advisor
Geological Sciences Graduate Program
Copyright by
Ryan Patrick Moyer
2008
ABSTRACT
Tropical small mountainous rivers (SMRs) may transport up to 33% of the total
carbon (C) delivered to the oceans. However, these fluxes are poorly quantified and
historical records of land-ocean carbon delivery are rare. Corals have the potential to
provide such records in the tropics because they are long-lived, draw on dissolved
inorganic carbon (DIC) for calcification, and isotopic variations within their skeletons are
useful proxies of palaeoceanographic variability. The ability to quantify riverine C inputs
to the coastal ocean and understand how they have changed through time is critical to
understanding global carbon budgets in the context of modern climate change. A seasonal
dual isotope (13C & 14C) characterization of the three major C pools in two SMRs and
their adjacent coastal waters within Puerto Rico was conducted in order to understand the
isotope signature of DIC being delivered to the coastal oceans. Additionally a 56-year
record of paired coral skeletal C isotopes (δ13C & Δ14C) and trace elements (Ba/Ca,
Mn/Ca, Y/Ca) is presented from a coral growing ~1 km from the mouth of an SMR. Four
major findings were observed: 1) Riverine DIC was more depleted in δ13C and Δ14C than
seawater DIC, 2) the correlation of δ13C and Δ14C was the same in both coral skeleton
and the DIC of the river and coastal waters, 3) Coral δ13C and Ba/Ca were annually
coherent with river discharge, and 4) increases in coral Ba/Ca were synchronous with the
ii
timing of depletions of both δ13C and Δ14C in the coral skeleton and increases in river
discharge. This study represents a first-order comprehensive C isotope analysis of major
C pools being transported to the coastal ocean via tropical SMRs. The strong coherence
between river discharge and coral δ13C and Ba/Ca, and the concurrent timing of increases
in Ba/Ca with decreases in δ13C and Δ14C suggest that river discharge is simultaneously
recorded by multiple geochemical records. Based on these findings, the development of
coral-based proxies for the history of land-ocean carbon flux would be invaluable to
understanding the role of tropical land-ocean carbon fluxes in the context of global
climate change.
iii
This work is dedicated to Aya, Jack, Dad,
and in loving memory of Cheryl L. Moyer
iv
ACKNOWLEDGMENTS
I would like to thank my advisor, Andrea Grottoli, and the members of my
dissertation committee, Jim Bauer, Anne Carey, Yo Chin, and Matt Saltzman for their
invaluable guidance and support during the preparation of this dissertation. Special
thanks are also extended to all members – past and present – of the stable isotope
biogeochemistry laboratories at both The University of Pennsylvania and The Ohio State
University for their invaluable support, advice, and friendship over the course of my time
at U. Penn and OSU.
This work was made possible through funding from the following agencies: The
Andrew Mellon Foundation, National Science Foundation Chemical Oceanography
Program (Grant #0610487), Geological Society of America, American Geophysical
Union, The American Association of Petroleum Geologists, and The Friends of Orton
Hall. Additionally, stipends were provided by the National Science Foundation GK-12
Program (U. Penn Access Science), OSU School of Earth Science graduate teaching
assistantships, and an OSU Presidential Fellowship.
I would like to thank Yohei Matsui and Mary Cathey for their patience and
dedication in keeping the laboratory running. Additional laboratory assistance and/or
facilities were provided by: A. Carey, R. Dodge, S. Goldsmith, S. Handwork, K. Helmle,
E. Keesee, C. Paver, D. Perkey, J. Southon, L. Swierk, and H. Wu. Logistical support in
v
the field was provided M. Canals and C. Pacheco at Guanica International Biosphere
Preserve, J. Salguero at Jobos Bay NERR, M. Salgado and F. Perez at the National Forest
Service, and C. Lileystrom and M. Abreu at Puerto Rico DRNA. Field sampling would
not have been possible without the in situ assistance of H. Anguerre, J. Bauer, M. Cathey,
J. Cruz, C. Malachowski, A. Grottoli, J. Troester, and B. Williams.
Finally, I would like to thank my family and friends for lending emotional, moral,
and sometimes even monetary support. Immeasurable thanks go to Aya, Dad, and Drew
for their love, support, and always being there when I need them; and to my
grandmothers - Audrey Minnich for continuing to ask “when are you going to graduate?”
and Evelyn Moyer for her love and support over the years. Thanks are extended to Jack
for continuing to remind me that it’s ok to be crazy sometimes. Lastly, I would like to
thank the inventors and modern makers of pizza for providing the sustenance to fuel my
body and brain over the course of compiling this dissertation.
vi
VITA
30 September 1976 ..………………………... Born, Reading Pennsylvania
1999 ..……………………………………….. B.S. Marine Science, Kutztown University
1999 – 2000 ………………………………… Pre-College Instructor, Marine Science
Consortium, Wallops Islands, Virginia
2001 – 2004 ………………………………… Research Assistant, National Coral Reef
Institute, Dania Beach, Florida
2003 ...………………………………………. M.S. Marine Biology, Nova Southeastern
University
2005 – 2008 ………………………………… Graduate Teaching Assistant, School of
Earth Sciences, The Ohio State University,
Columbus, Ohio
PUBLICATIONS
Research Publications
1.
Riegl B, Moyer RP, Walker BK, Kohler KE, Dodge RE, Gilliam DS. (2008) A tale
of germs, storms, and bombs: Geomorphology and coral assemblage structure at Vieques
(Puerto Rico) compared to St. Croix (U.S. Virgin Islands). Journal of Coastal Research.
24:1008-1021.
2.
Riegl B, Moyer RP, Morris LJ, Virnstein RW, Purkis SJ. (2005) Distribution and
seasonal biomass of drift macroalgae in the Indian River Lagoon (Florida, USA)
estimated with acoustic seafloor classification (QTCView, Echoplus). Journal of
Experimental Marine Biology and Ecology. 326:89-104.
3.
Moyer RP, Riegl B, Banks K, Dodge RE. (2005) Assessing the accuracy of
acoustic seabed classification for mapping coral reef environments in South Florida
(Broward County, USA). Revista de Biologia Tropical (Int. J. Trop. Biol.) 53(Supp.
1):175-184.
vii
4.
Riegl B, Moyer RP, Morris L, Virnstein R, Dodge RE. (2005) Determination of the
distribution of shallow-water seagrass and drift algae communities with acoustic seafloor
discrimination. Revista de Biologia Tropical (Int. J. Trop. Biol.) 53(Supp. 1):165-174.
5.
Moyer RP, Riegl B, Banks K, Dodge RE (2003) Spatial patterns and ecology of
high-latitude benthic communities on a South Florida (Broward County, USA) relict reef
system. Coral Reefs. 22(4): 447-464.
FIELDS OF STUDY
Major Field: Geological Sciences
Area of Emphasis: Marine Biogeochemistry
viii
TABLE OF CONTENTS
Page
Abstract…………………………………………………………………………..........
ii
Dedication……………………………………………………………………….......... iv
Acknowledgements……………………………………………………………………
v
Vita……………………………………………………………………………............. vii
List of Tables……………………………………………………………….................. xiii
List of Figures…………………………………………………………………............ xiv
Chapters:
1.
2.
Introduction…………………………………………………………................
1
Significance…………………………………………........................................
Background…………………………………………………………………....
Physical Setting………………………………………………...................
Patterns of Precipitation in Puerto Rico……………………………….....
Carbon in River Catchments and the Coastal Ocean………………….....
Coral Biology & Skeleton Formation……………………………….........
Carbon Isotopes in Coral Skeletons………………………………………
Trace Elements in Coral Skeletons………………………………….........
Interpreting Land-Ocean Carbon Flux in Coral Skeletal Geochemistry…
Research Proposal…………………………………………………………..…
Design of the Study………………………………………………..……....
Chapter 2: Carbon isotope geochemistry of two tropical small
mountainous river catchments and adjacent coastal waters in Puerto
Rico…………………………………………………………………......…
Chapter 3: Coral skeletal dual carbon isotope (δ13C & Δ14C) record of
the delivery of terrestrial carbon to the coastal waters of Puerto Rico…..
Chapter 4: A multi-proxy record of terrestrial inputs to the coastal
ocean using trace elements (Ba/Ca, Mn/Ca, Y/Ca) and carbon isotopes
(δ13C, Δ14C) in a coral skeletal core……………………………………...
Broader Impacts…………………………………………………………….…
Literature Cited………………………………………………………………..
1
3
3
5
7
12
16
18
19
21
22
Carbon isotope geochemistry of two tropical small mountainous river
catchments and adjacent coastal waters in Puerto Rico…………………….....
ix
25
26
28
29
30
43
Page
Abstract……………………………………………………………………….. 44
Introduction…………………………………………………………………… 46
Methods……………………………………………………………………….. 49
Study areas……………………………………………………………….. 49
Field sampling…………………………………………………………..... 52
Sample preparation & concentration measurements…………………….. 53
δ13C measurements……………………………………………………….. 55
Δ14C measurements……………………………………………………..... 56
Data analysis……………………………………………………………... 57
Results………………………………………………………………………… 60
Dissolved inorganic carbon…………………………………………….... 60
Dissolved organic carbon……………………………………………...… 61
Particulate organic carbon………………………………..…………….. 64
Discussion……………………………………………………………………. 64
Sources of inorganic carbon to tropical SMRs…………………………... 65
Sources of organic carbon (DOC & POC) to tropical SMRs…………..... 66
Comparison of SMRs in Puerto Rico to other global river systems……… 68
Sources of carbon to coastal waters……………………………………... 70
Land-ocean carbon flux and estuarine mixing in tropical SMRs……...
72
Summary………………………………………………………………...... 74
Acknowledgements…………………………………………………………… 75
Literature Cited……………………………………………………………….. 76
Tables…………………………………………………………………………. 85
Figures……………………………………………………………………….... 91
3.
Coral skeletal dual carbon isotope (δ13C & Δ14C) record of the delivery of
terrestrial carbon to the coastal waters of Puerto Rico………………………... 103
Abstract………………………………………………………………………..
Introduction……………………………………………………………………
Materials & Methods…………………………………………………………..
Study area…………………………………………………………………
Coral sampling……………………………………………………………
Water sampling………………………………………………………..….
Stable isotope analyses……………………………………………………
Radiocarbon analyses…………………………………………………….
Data Analysis……………………………………………………………..
Results…………………………………………………………………………
Coral growth & chronology………………………………………….…..
Coral skeletal δ13C & Δ14C……...…………………………….…………
DIC δ13C & Δ14C……...……………………………………………...…..
Discussion……………………………………………………………………..
Coral growth……………………………………………………………..
x
104
105
108
108
109
111
112
113
114
117
117
117
118
119
119
Page
Coral skeletal δ C & Δ C……...…………………………….………… 120
Relationship between DIC and coral skeletal isotopes………………….. 123
Relationship between river discharge and coral skeletal isotopes at high
sampling resolution……………………………………………………… 124
Conceptual model………………………………………………………... 125
Implications for proxy records…………………………………………... 128
Summary…………………………………………………………………. 129
Acknowledgements…………………………………………………………… 129
Literature Cited……………………………………………………………….. 130
Tables…………………………………………………………………………. 137
Figures………………………………………………………………………… 139
13
4.
14
A Multi-Proxy Record of Terrestrial Inputs to the Coastal Ocean Using Trace
Elements (Ba/Ca, Mn/Ca, Y/Ca) and Carbon Isotopes (d13C, D14C) in a
Coral Skeletal Core…………………………………………………………… 148
Abstract………………………………………………………………………..
Introduction……………………………………………………………………
Materials & Methods…………………………………………………………..
Geographical setting…………………………………………………..….
Coral sampling………………………………………………………..…..
Isotopic analyses………………………………………………………….
Coral trace element measurement via laser ablation inductively coupled
Plasma mass spectrometry……………………………………………..…
Sampling and measurement of trace elements in ambient waters………..
Data analysis…………………………………………………………..….
Results…………………………………………………………………………
Coral trace elements……………………………………………………...
Trace elements in natural waters…………………………………………
Coral δ13C & Δ14C………………………………………………………...
Discussion……………………………………………………………………..
Coral Ba/Ca………………………………………………………………
Relationship of coral Ba/Ca, δ13C, and Δ14C……………………………..
Coral Mn/Ca and Y/Ca.………………………………………..…………
Implications for proxy records……………………………………………
Summary…………………………………………………………………..
Acknowledgements…………………………………………………………...
References…………………………………………………………………….
Tables…………………………………………………………………………
Figures………………………………………………………………………...
xi
149
150
153
153
154
154
155
157
159
160
160
161
162
163
163
167
168
171
173
174
175
181
182
5.
Page
Summary and Future Research………………………………………………. 190
Isotopic character and concentration of carbon delivered to the tropical
coastal ocean by small mountainous rivers…...……………………………… 191
Coral Records of Terrestrial Carbon Delivery to the Coastal Ocean……...…. 193
Future Work………………………………………………………………….. 195
List of References…………………………………………………………………….. 195
Appendices……………………………………………………………………………. 217
Appendix A: Raw Coral Isotope Data…………………………………..……..
Appendix B: High Resolution Coral Stable Isotope Data……………………..
Appendix C: Bi-Weekly Smoothed River Discharge and Coral Trace Element
Data…………………………………………………………………………….
Appendix D: Monthly Smoothed River Discharge and Coral Trace Element
Data……………………………………………………………..……………...
xii
217
225
229
258
LIST OF TABLES
Table
Page
2.1
Riverine and seawater dissolved inorganic carbon data...…………………...... 85
2.2
Riverine and seawater dissolved organic carbon (DOC) data….….…...……... 86
2.3
Riverine and seawater particulate organic carbon (POC) data………….…….. 87
2.4
Results of a fully factorial model III analysis of variance for dissolved
inorganic, dissolved organic, and particulate organic carbon concentrations,
and stable (δ13C) and radiocarbon (Δ14C) data................................................... 88
2.5
Estimated fluxes of dissolved inorganic carbon from land to the coastal ocean
in Puerto Rico……………………….………………………………………… 89
2.6
Estimated fluxes of dissolved organic carbon from land to the coastal ocean
in Puerto Rico…………………………………….…………………………… 90
3.1
Stable (δ13C) and radiocarbon (Δ14C) isotope values measured in the
dissolved inorganic carbon (DIC) of river and seawater at the Rio Fajardo
catchment in eastern Puerto Rico…………………………………...………… 137
3.2
Results of a fully factorial model III analysis of variance (ANOVA) for
both DI-δ13C and DI-Δ14C data……………………………………………….. 138
4.1
Trace element data in natural waters of the Fajardo study area.……………… 181
5.1
Raw coral isotope data (δ13C and Δ14C) presented and discussed in
Chapters 3 and 4………………………………………………………………. 218
6.1
Stable carbon isotope (δ13C) data analyzed at high resolution (0.1 mm) and
discussed in Chapter 3………………………………………………………… 226
7.1
Bi-weekly smoothed Rio Fajardo discharge and coral trace element data
presented and discussed in Chapter 4…………………………………………. 230
8.1
Monthly smoothed Rio Fajardo discharge and coral trace element data
presented and discussed in Chapter 4………………………………………… 259
xiii
LIST OF FIGURES
Figure
1.1
1.2
Page
Conceptual model of the predicted relationships of carbon isotopes (δ13C &
Δ14C) of the overlying vegetation, soil organic matter, river water, coastal
ocean and coral skeletons in Puerto Rico………………………………..…….
11
Map showing the location of the Fajardo and Guanica study areas within
Puerto Rico, and field sampling sites within each study area…………………
23
2.1
Landsat 7 images showing the location of study areas and sampling sites
within Puerto Rico……………………………………………..……………… 91
2.2
Seasonal dissolved inorganic carbon concentration vs. salinity plots for
Guanica and Fajardo………..………………………………….………….......
92
2.3
Seasonal dissolved inorganic carbon stable isotopes vs. salinity plots for
Guanica and Fajardo…………….…………………………..………………… 93
2.4
Seasonal dissolved inorganic carbon radiocarbon isotopes vs. salinity plots
for Guanica and Fajardo…………………….…………………………………
94
2.5
Seasonal dissolved organic carbon concentration vs. salinity plots for
Guanica and Fajardo………………………………………………...………… 95
2.6
Seasonal dissolved organic carbon stable isotopes vs. salinity plots for
Guanica and Fajardo………………………………………………………...… 96
2.7
Seasonal dissolved organic carbon radiocarbon isotopes vs. salinity plots for
Guanica and Fajardo………………………………………….………….......... 97
2.8
Carbon isotope source diagrams for dissolved inorganic carbon……………... 98
2.9
Carbon isotope source diagrams for dissolved organic carbon……………..…
2.10
Carbon isotope source diagrams for particulate organic carbon …………...… 100
2.11
Radiocarbon ages of riverine particulate organic carbon reported in this study
and from other tropical/sub-tropical, temperate, and arctic rivers……………. 101
xiv
99
Figure
Page
2.12
Radiocarbon ages of riverine dissolved organic carbon reported in this study
and from other tropical/sub-tropical, temperate small mountainous, and large
temperate rivers…………………………………..…………………………… 102
3.1
Geographic setting of the study……………………………………………..… 139
3.2
X-radiograph positive prints of the top two sections of the Fajardo coral core. 140
3.3
Stable- (δ13C) and radiocarbon (Δ14C) values measured for the Fajardo coral
core (1948 – 2004)………………………………………………….………… 141
3.4
Results of cross-spectral analysis between Rio Fajardo discharge and the
Fajardo coral skeletal δ13C time series…………………………...…………… 142
3.5
Stable- (δ13C) and radiocarbon (Δ14C) anomalies in the Fajardo coral core
for the period 1955 - 2004……………………………………………..……… 143
3.6
Fajardo coral skeletal δ13C vs. Δ14C anomalies……………………………..… 144
3.7
Fajardo river and coastal seawater DI-δ13C vs. DI-Δ14C…………………...… 145
3.8
High resolution (0.1 mm) stable carbon isotope anomalies in the Fajardo
Coral core for the period 2002 – 2004………………………………………… 146
3.9
Conceptual model showing the flow of major sources of carbon from within
the Rio Fajardo catchment to the coastal ocean…………………………….… 147
4.1
Study area………………………………………………………………...…… 182
4.2
X-radiograph positive prints of the Fajardo coral core…………………..…… 183
4.3
River discharge and coral trace element ratio time series…………………..… 184
4.4
Results of cross-spectral analysis………………………………………...…… 185
4.5
Stable- (δ13C) and radiocarbon (Δ14C) isotope anomalies in the Fajardo coral
skeleton for the period 1955 - 2004………………….…………………...…… 186
4.6
Concentrations of barium, manganese, and yttrium along a salinity gradient
from the Rio Fajardo to the coastal ocean…………………………………..… 187
4.7
Fajardo coral δ13C and Δ14C anomalies, Ba/Ca, and Rio Fajardo discharge
from 1999 to 2004…………………………………………………………….. 188
xv
Figure
4.8
Page
Fajardo coral δ13C and Δ14C anomalies, and Ba/Ca from 1950 to 1956……… 189
xvi
CHAPTER 1
INTRODUCTION
SIGNIFICANCE
The quantity and character of terrestrially-derived carbon to the coastal ocean, and
its impact on the global carbon cycle, are only beginning to be understood in temperate
environments due to a small but growing body of reliable terrestrial, river and seawater
geochemical measurements. In the tropics, these measurements are thus far restricted to
recent measurements on the largest of rivers (i.e. the Amazon), and are otherwise rare or
non existent. The quantity and character of both organic and inorganic carbon delivered
to the coastal ocean is relatively unknown for small mountainous tropical rivers, despite
the fact that these rivers are thought to deliver a significant amount of terrestriallyderived carbon to the coastal oceans [Lyons et al., 2002]. In addition, dramatic changes
in land-use have occurred in tropical regions over the last century, and are driving
dramatic alterations in tropical carbon cycling on land and in large rivers systems such as
the Amazon [Houghton et al., 2000; Mayorga et al., 2005]. Such changes will likely have
a significant impact on the quantity and character of carbon delivered to coastal oceans.
The lack of information on the transport and delivery of carbon to the ocean in tropical
systems, particularly from small mountainous rivers, represents a major gap in the
collective understanding of both local and global carbon cycles. Carbon isotope and trace
1
element signatures archived in the skeletal records of corals growing near the mouths of
small tropical rivers may help fill this gap in knowledge by providing a history of carbon
delivery to the tropical coastal ocean over the past century.
Corals deposit calcium carbonate skeleton in distinct annual bands, can grow for
several centuries, and draw both directly and indirectly on seawater dissolved inorganic
carbon (DIC) for calcification. In areas where coral reefs occur in close proximity to the
mouths of small mountainous tropical rivers and streams, the stable carbon (δ13C) and
radiocarbon (Δ14C) values of the coastal seawater DIC are likely influenced by the δ13C
and Δ14C of the organic and inorganic carbon of the adjacent watershed during periods of
sustained high riverine input to the coastal ocean. Thus, corals adjacent to rivers have the
capacity to provide a reliable history of carbon delivery to the tropical coastal ocean.
Puerto Rico is an ideal study location as there is a wealth of meteorological and
river discharge data available for the last several decades, and much is known about local
land-use history over the past century. Corals are also found growing near the mouths of
several small mountainous rivers and measurements of soil organic matter and river
dissolved organic matter concentrations have recently been made [von Fischer and
Tiezen, 1995; Aitkenhead-Peterson et al., 2003; Marin-Spiotta et al., 2008]. The climate
of Puerto Rico ranges from wet-tropical to semi-arid. River catchments range from
predominantly deforested to predominantly-forested. Thus, the natural setting provides a
potentially large source of variation to the carbon isotopic signal of riverine and coastal
ocean waters within insular Puerto Rico.
The research presented herein draws upon carbon isotope methods from several
inter-related Earth science fields. The work also connects river, coastal ocean, and coral
2
carbon isotope (13C and 14C) geochemistry in order to evaluate the transfer of terrestrial
carbon to the tropical coastal ocean via small mountainous rivers. The work provides
thorough first-order quantitative analyses of the quantity and character of carbon
delivered to the coastal ocean via small mountainous tropical rivers, and of land-derived
geochemical signals preserved in coral skeletons. This research also furthers the
collective understanding of the important role small tropical rivers play in both local and
global carbon cycling from terrestrial to marine environments. This work also shows that
corals can provide a history of land-ocean carbon transfer in areas of the Earth where
long-term records are scarce or non-existent. Such records are critical to understanding
carbon cycling in the context of modern global climate change. Beyond carbon cycling,
the work also has implications for managers of tropical terrestrial and tropical resources.
A growing body of literature suggests that corals are not immune to processes happening
on land (Furnas 2003; McCulloch et al. 2003; Marion et al. 2005). This work adds to this
body of literature by providing a geochemical link between terrestrial systems and corals.
Therefore this information can be used by resource managers to make informed decisions
that are beneficial to both terrestrial and adjacent marine environments.
BACKGROUND
Physical Setting
The Commonwealth of Puerto Rico (N 18.25°, W 066.5°) is located east of the
island of Hispañola in the northeastern Caribbean Sea, and is the smallest archipelago in
the Greater Antilles. The main island of Puerto Rico encompasses an area of 8,802 km2
and is the largest island of the archipelago. Puerto Rico lies at the boundary between the
3
Caribbean and North America plates and is composed of Cretaceous to Eocene volcanic
and plutonic rocks overlain by Oligocene to Holocene carbonates and other sedimentary
rocks. The oldest rocks (Jurassic) occur at the Sierra Bermeja in the southwestern part of
the island. Puerto Rico emerged as a result of volcanism and deformation caused by
tectonic activity along the Puerto Rico Trench subduction zone [Morelock et al., 2000].
Due to these processes, followed by deposition and weathering of younger limestones
along the margins of the island platform, three principal geomorphic regions exist. (1)
The Cordillera Central is an east-west mountain chain with a mean elevation of 762 m
and a peak elevation of 1340 m [Carlson, 1952]. This mountain ridge dominates the
interior of Puerto Rico and is composed of faulted and folded Cretaceous-Tertiary age
volcaniclastic and sedimentary rocks with igneous intrusions. (2) Flanking the perimeter
of the Cordillera Central is a continuous margin of coastal lowlands composed of
Miocene age limestone and karst regions across the north-central, northwestern, and
south-central portions of the island [Schneidermann et al., 1976]. (3) A discontinuous
apron of Quaternary alluvium which has been weathered and transported from the steep
slopes of the Cordillera Central to fill drainage valleys and other low-lying areas of the
modern coastal plain.
The landscape of Puerto Rico has experienced major shifts in land-use practices
within the last several centuries as a result of economic and population growth. Puerto
Rico had fewer than 4000 inhabitants in 1600 [Grau et al., 2003], but by 1899, the
population had reached 953,243 [Carlson, 1952]. Land cover at this time consisted of
55% pasture [Grau et al., 2003], 21% agricultural land [Gellis, 2003], and 24% natural
vegetation. The use of land for agriculture, driven by thriving sugar cane production and
4
export, peaked in 1939 when 85% of the landscape was pasture or cropland [Grau et al.,
2003]. By 1950, forest cover in Puerto Rico decreased to < 6% of the total land area
[Zimmerman et al., 2007]. Since the 1950’s, the economy of Puerto Rico has made a
major shift away from agriculture and has become heavily based on industry and tourism.
Accordingly, agricultural land cover has decreased [Grau et al., 2003], with many areas
becoming re-forested or developed for urbanization [Zimmerman et al., 2007]. Currently,
the population of Puerto Rico is 3,898,000 [Lopez et al. 2001] and the land-use is 42%
forested land, 37% grassland or abandoned pasture, 8% agriculture, and 11% urban or
partially developed lands [Helmer et al., 2002].
Patterns of Precipitation in Puerto Rico
Puerto Rico receives rainfall in every month of every year and average annual
rainfall for the entire island is approximately 1,750 mm yr-1 [Schneidermann et al., 1976].
Precipitation patterns are primarily influenced by the northeasterly trade winds and the
presence of the Cordillera Central which produces a dramatic orographic effect [SantosRomán et al., 2003]. Cooler temperatures associated with the high elevation of the
mountains condense the moist air carried by the trade winds, resulting in large amounts
of rainfall in the northeast of the island, and substantially less rain along a northeast to
southwest gradient. As a result of this orographic effect, areas of the Luquillo Mountains
in northeastern Puerto Rico receive over 4,000 mm yr-1 of precipitation while the
southwestern regions of the island typically only receive ~500 mm yr-1 [Lugo and
Garcia-Martino, 1996]. Coupled ocean-atmospheric systems such as the El NiñoSouthern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) are responsible
5
for the interannual variability of rainfall patterns island-wide, with the NAO having the
strongest relationship to interannual climatic variability observed within Puerto Rico
[Malmgren et al., 1998].
Precipitation over the entire island also exhibits seasonal variability within each
year, with most areas experiencing a wet season during the months of June through midJanuary, and a dry season from mid-January through May [Calvesbert, 1970]. Due to
Puerto Rico’s geographic location and relatively small size, the season variability is not
driven by climatic associations with tropical monsoons or the Inter-Tropical Convergence
Zone (ITCZ) [Walsh, 1997]. Instead, the annual variability of rainfall within Puerto Rico
is driven by several major natural disturbance phenomena [Scatena et al., 2005].
Cyclonic systems, including hurricanes and tropical waves, typically only occur in the
months of June through November and are capable of producing intense localized rain
events, although are not responsible for some of the largest precipitation events on record
in Puerto Rico [Scatena et al., 2005]. Non-cyclonic, inter-tropical systems produce some
of the heaviest rainfall events throughout the entire island, which typically occur during
the months of May through December. Extra-tropical frontal systems (cold fronts)
originate north of the tropics during winter months, and can bring rainfall to Puerto Rico
during the months of December through April. The co-occurrence of cold fronts and noncyclonic inter-tropical systems can produce locally heavy rainfall events during the
months of December and January.
6
Carbon in River Catchments and the Coastal Ocean
The stable carbon isotopic composition (δ13C = the per mil deviation of 13C:12C
relative to the Vienna Pee Dee belemnite (VPDB) standard) [Coplen, 1996] of surface
soil and living plant organic matter is influenced by the vegetative cover of the landscape.
Most pasture grasses and some tropical agricultural crops (e.g. sugarcane) use the C4
photosynthetic pathway resulting in an enrichment of heavier carbon isotopes (13C) in
their tissues. Conversely, most tropical trees use a C3 pathway, and have tissues that are
not so enriched with 13C [Smith and Epstein, 1971]. In Puerto Rico, this natural
differentiation has resulted in surface soil organic matter and overlying vegetation of
forested areas (C3 plants) having average δ13C values of -26‰, while pastures, fields, and
associated vegetation (C4 plants) have average δ13C values of -15 ‰ [von Fischer and
Tieszen, 1995].
Rivers link terrestrial and coastal marine ecosystems. They are sites of intense soil
organic matter processing, thus influencing the abundance, composition, and timing of
carbon discharged to the coastal ocean. Soil organic matter may or may not age
significantly on land prior to mobilization by rivers and estuaries [Kao and Liu, 1996;
Cole and Caraco, 2001; Masiello and Druffel, 2001; Raymond and Bauer, 2001a,b; Blair
et al., 2003]. Prior to, or during mobilization, most terrestrially-derived organic carbon is
broken down and transported by rivers as dissolved organic carbon (DOC) [Hope et al.,
1994; Aitkenhead-Peterson et al. 2003, 2005], which is further converted into DIC via
respiration or photo-oxidation during transport to the coastal ocean [Raymond and Bauer,
2001a; Mopper and Kieber, 2002]. Estuarine mixing is also plays an important role in
the degradation and cycling of riverine DOC, where a significant portion of terrestrial
7
carbon is altered in mid-salinity estuarine waters [Robertson and Alongi, 1995; Wang et
al. 2004].
Particulate organic carbon (POC) is also transported to the coastal ocean via rivers
and streams, and in systems where data on both dissolved and particulate forms are
available, riverine POC is frequently more abundant than DOC [Meybeck, 1982;
Alexander et al., 1998; Carey et al., 2005]. Anthropogenic influences such as changes in
land-use or river dam construction have greatly influenced fluxes of POC in river systems.
The amount of POC generally increases downstream due to increased runoff caused by
land-use change [Milliman and Meade, 1982; Meade, 1996], but decreases downstream
of river dams. Undisturbed mountainous rivers, including those in the tropics, have been
found to have the most highly aged POC [Kao and Liu, 1996; Komada et al. 2004, 2005]
and bulk sediments [Blair et al., 2003; Leithold et al., 2006] observed in any global river
systems.
Radiocarbon (14C) is produced naturally in the stratosphere and was also created
anthropogenically as a result of thermonuclear weapons testing in the 1950’s and early
1960’s. In the northern hemisphere this anthropogenic source, or 'bomb' 14C, resulted in a
near doubling of 14C activity in the atmosphere and terrestrial carbon bearing materials.
Atmospheric bomb 14C reached a peak value in 1963 in the northern hemisphere and has
been decreasing since that time due to exchange between and dispersal within the Earth’s
carbon reservoirs. De Vries [1958] was the first to identify this excess bomb 14C
inventory, and its ubiquitous presence within the earth's biosphere has enabled it to be
used as a tracer to investigate mechanics of carbon mixing and exchange processes.
8
The land-use within a catchment will also influence the apparent age of carbon
delivered to tropical rivers, which is measurable using Δ14C (the per-mil deviation of
14
C:12C relative to the 95% Oxalic Acid-1 standard). Recent studies have shown that
surface soils in Puerto Rico forests and abandoned pastures all contain bomb radiocarbon,
indicating that they are composed primarily of younger organic material produced since
the 1950’s [Marin-Spiotta et al. 2008]. Meanwhile, soils from agricultural catchments
typically have relatively older 14C ages (lower Δ14C values) compared to the undisturbed
forested sites due to the constant overturning of older soil layers through tillage and
harvesting. Since agricultural practices tend to expose older organic matter, the 14C ages
of river water DOC and POC should be older (lower Δ14C values) within predominantly
agricultural drainage basins. Thus during times of increased river discharge (i.e. the wet
season), the Δ14C of seawater DIC, DOC and POC should also carry a distinct terrestrial
signature that is strongly indicative of the land-use and vegetative cover within the
catchment.
In temperate rivers and in the Amazon and its headwaters, δ13C values range from
-31.9 to -25.5‰ for DOC and -17.1 to -4.9‰ for DIC [Raymond and Bauer, 2001a;
Mayorga et al., 2005; Aufdenkampe et al., 2007]. These values reflect isotopically
depleted terrestrial plant or soil material as sources of the carbon being transported within
the associated catchment. The 14C ages of DOC and POC in these same systems range
from ~1500 ybp to modern and ~4000 ybp to modern, respectively [Raymond and Bauer,
2001a; Mayorga et al., 2005]. The large range in age of organic material also reflects
differences in the source material being transported within these river catchments. In
Puerto Rico, it is expected that the δ13C of riverine DOC, DIC, and POC in forested
9
basins (C3-plant dominated) should be isotopically more depleted (lower δ13C values)
than in rivers with catchments that are predominantly C4 pasture or agricultural crops.
Conversely, it is expected that older organic material (lower Δ14C) is derived from within
primarily agricultural catchments where older soil is being brought to the surface and
mobilized into rivers. During the wet season when river discharge is greater, seawater
adjacent to agricultural catchments should also have older DOC and POC, due to the
delivery of older carbon to the coastal ocean (Fig. 1.1A). This ‘land-print’ isotopic
signature should distinguish individual catchments and be most discernable during the
wet season (Fig. 1.1A, C) since increased river discharge typically result in freshwater
plumes that remain in coastal waters on timescales of days to weeks. Conversely in the
dry season, river discharge is typically minimal and in turn, the contribution of
terrestrially derived carbon to the coastal ocean is expected to be negligible (Fig. 1.1B,
D).
Information gained from using both δ13C and Δ14C in temperate river DOC has
been especially effective for calculating sources, sinks, and residence times of organic
matter and has been shown to be more effective than using either isotope alone in both
temperate (Raymond & Bauer 2001a,b) and tropical (Mayorga et al. 2005) river systems.
Notably this is due to low susceptibility of natural abundance isotopes to diagenetic
effects acting upon organic molecules paired with the greater dynamic range of Δ14C
compared to δ13C (Raymond & Bauer 2001b). This dual-isotope approach proposed for
this study will optimize the results in a tropical rivers and the coastal ocean.
10
Figure 1.1: Conceptual model of the predicted relationships of carbon isotopes (δ13C &
Δ14C) of the overlying vegetation, soil organic matter, river water, coastal ocean and
coral skeletons in Puerto Rico. Wet (A, B) vs. dry (C, D) season, and agricultural (A, C)
vs. forested (B, D) land-use influences are shown. Agricultural land-use (A, C) is
representative of modern Guanica land cover and pre-1960 land cover for all of Puerto
Rico. Forested land-use is representative of post-1960 Fajardo land-cover. DIC, DOC,
POC and coral δ13C and Δ14C estimates are based on measurements made in this
dissertation and soil organic matter δ13C and Δ14C values are taken from von Fischer and
Tieszen [1999] and Marin-Spiotta et al. [2008], respectively. 14C relative ages range from
young (‘yg’) to ‘old’, with intermediate values designated as ‘aged’.
11
Coral Biology & Skeleton Formation
Reef-building corals are benthic animals in the Family Cnidaria, Order
Scleractinia, and Class Anthozoa. The body plan of Scleractinian corals suitable for
geochemical studies comprises a living polyp overlaying an inorganic calcium carbonate
(CaCO3) skeleton. The body wall of the polyp is composed of two tissue layers, an
epidermis (external) and gastrodermis (internal), encasing a gelatinous mesoglea.
Structurally these tissues form tentacles, an oral opening used for both ingestion and
excretion, and a gastrovascular cavity around a radially-symmetrical body plan. Most
coral species are colonial, with individual polyps interconnected by a lateral coenosarc to
form a massive coral colony. Nearly all of the shallow-water reef-building corals have a
symbiotic relationship with photosynthetic single-celled dinoflagellates (zooxanthellae)
which live within the gastrodermis. In exchange for photosynthetically-fixed carbon
provided by the zooxanthellae, the coral host provides nutrients vital to the survival of the
symbiotic algae [Muscatine and Cernichiari, 1969; Porter, 1976; Muscatine and Porter,
1977; Muscatine et al., 1989]. Corals reproduce both sexually through the release of
eggs and/or sperm, or egg-sperm bundles into the water column, and asexually by
fragmentation.
Skeletogenesis in corals [see reviews by Gattuso et al., 1999; Cohen and
McConnaughey, 2003; Allemand et al., 2004] occurs when calcium cations (Ca2+) and
carbonate anions (CO32-) combine to form CaCO3 in the form of the aragonite mineral
according to the following chemical reaction:
Ca2+ + 2HCO3- Ù CaCO3 + CO2 + H2O
12
(Equation 1.1)
Although both the Ca2+ and CO32- ions occur in high concentrations in seawater, CaCO3
typically does not precipitate without biological mediation in well-mixed seawater
[Barnes and Lough, 1989].
In order for calcification to occur in corals, both Ca2+ and CO32- need to become
supersaturated within the extracellular sub-membrane space (SMS) of the animal.
Skeletogenesis then occurs in isolation from direct contact with ambient seawater
[Barnes and Chalker, 1990] within the SMS located between the basal epidermis and the
underlying skeleton. Although it has been suggested that some ions (e.g. HCO3- and
Ca2+) can enter the SMS via extracellular channels [McConnaughey, 1989a,b], the
primary mechanism of Ca2+ delivery to the SMS is active pumping via protein-mediated
transport [McConnaughey, 1989a; McConnaughey and Whelan, 1997; Cohen and
McConnaughey, 2003].
The delivery of CO32- to the SMS is dictated by the equilibrium it shares with
carbon dioxide (CO2), and bicarbonate (HCO3-) in aqueous solutions. The major
components of this carbonate equilibrium are given by the equation (Equation 1.2):
CO2 (g) + H2O (l) Ù H2CO3 (aq) Ù H+ (aq) + HCO3- (aq) Ù 2H+ (aq) + CO32- (aq)
Carbon dioxide
Carbonic acid
Bicarbonate
Carbonate
Bicarbonate is the dominant species in the equilibrium at a typical seawater pH of ~8.1.
Since it is a charged particle, CO32- cannot diffuse across biological membranes; instead,
the only entry into the SMS is via extracellular channels, vacuoles, or active transport of
13
water ingested into the lower tissue layers of the polyp [McConnaughey, 1989a,b; Cohen
and McConnaughey, 2003].
However, the small amount of HCO3- delivered to the SMS via these pathways
does not account for the full amount of CO32- required by the coral for skeletogenesis
[McConnaughey, 1991]. Since CO2 is a neutral molecule, and therefore able to diffuse
across biological membranes, it has been proposed as another source of inorganic carbon
to the SMS. Although CO2 is found at low concentrations within seawater, it is possible
for corals to produce additional CO2 on the outer surface of their tissues using an
enzyme-mediated reaction [McConnaughey, 1991]. This in turn creates a concentration
gradient which drives CO2 into the tissue where it can then be used either by the
zooxanthellae for photosynthesis or diffused into the SMS of the coral for skeletogenesis
[McConnaughey, 1989b]. CO2 is also produced by both the coral and zooxanthellae
during respiration, where it can be recycled for photosynthesis, diffused into the SMS for
calcification, or released into the ambient seawater [Falkowski et al., 1984; Furla et al.,
2000].
Corals are found in tropical oceans throughout the world, and can grow for
several hundred years. Corals deposit their CaCO3 skeletons in discrete annual bands,
with each annual band consisting of a high- and low-density couplet [Knutson et al.,
1972; Buddemeier and Kinzie, 1976]. At discrete intervals, the polyp detaches itself from
the existing skeleton, raises itself, and begins to precipitate a new layer of skeleton.
Differences in skeletal density are caused by differential thickening of fine horizontal
bands and vertical ridges within the skeletal architecture [Dodge et al., 1992].
Additionally, Taylor et al. [1993] suggest that as much as half the total skeletal mass
14
could be added after initial deposition due to secondary thickening of the structural
elements. The timing of the formation of high- and low-density bands varies according
geographic location and corresponds to differing environmental conditions experienced
by the coral over the course of a year. Generally, high-density bands form during suboptimal conditions and low density bands during optimal conditions. In Puerto Rico, low
density bands are thought to be formed during winter months [Watanabe et al., 2003,
Smith et al., 2006]. Coral colony age can be determined by counting the annually banded
density couplets in a manner similar to that which has been applied to tree rings. Xradiography of the coral skeleton reveals the paired high- and low-density couplets, and
these have been interpreted to correspond to one year of coral growth [Knutson et al.,
1972; Buddemeier and Kinzie, 1976; Hudson et al., 1976; Barnes and Lough, 1993;
Barnes and Taylor, 1993].
The unaltered aragonite of coral skeletons retains a permanent record of past
changes in seawater chemistry through a variety of geochemical proxies. Once deposited,
the aragonite of calcifying organisms is not readily dissolved due to the super-saturation
of aragonite in the surface ocean. Furthermore, there is no evidence that coral aragonite
exchanges with carbonate ions in the seawater [Pearse, 1970], as supported by
radiometric dating of corals which can only work if the aragonite exhibits closed system
behavior [Dodge and Thomson, 1974; Edwards et al., 1987]. Thus, corals provide a
faithful record of environmental conditions that existed at the time of skeletal deposition
[see reviews by Druffel, 1997; Gagan et al. 2000; Grottoli, 2002; Eakin and Grottoli,
2006; Grottoli and Eakin, 2007]. Recent studies have demonstrated that tropical corals
can preserve the history of tropical climate and surface ocean variability at resolution
15
ranging from sub-annual [e.g. Fairbanks and Dodge, 1979; Swart, 1983; Leder et al.,
1996; Smith et al., 2006], to centennial [e.g. Cole et al., 1993; Dunbar et al., 1994;
Linsley et al., 2000; Tudhope et al., 2001; Kilbourne et al., 2007; Fleitmann et al., 2007].
Carbon Isotopes in Coral Skeletons
Mounding corals are long lived (300+ yrs.) and deposit their skeletons in distinct
annual bands. Such coral growth records can be combined with the isotope and/or trace
metal geochemistry preserved within the coral skeleton to serve as proxies for a host of
paleo-environmental events and conditions over the life span of the coral [Hudson,
1981a,b; Dodge and Lang, 1983; Druffel, 1997; Gagan et al., 2000; Grottoli, 2002; Eakin
and Grottoli, 2006; Grottoli and Eakin, 2007]. Sustained peak river discharge events are
distinctly visible as UV-sensitive fluorescent bands and/or as elevated levels of elemental
barium in some coral skeletons [Isdale, 1984; Barnes and Taylor, 2001; McCulloch et al.,
2003], indicating that corals skeletons can serve as recorders river-water discharge pulses.
Coral skeletal δ13C values are regulated by both metabolic and kinetic reactions
that fractionate skeletal carbon [McConnaughey et al., 1997; Grottoli, 1999; Grottoli,
2001]. However, in most healthy shallow-water hermatypic corals, skeletal δ13C is
largely influenced by metabolic fractionation due to changes in photosynthetic and
heterotrophic rates of carbon acquisition [Swart, 1983; Muscatine et al., 1989; Grottoli
and Wellington, 1999; Reynaud-Vaganay et al., 2001; Grottoli, 2002; Ferrier-Pages et
al., 2003; Swart et al., 2005]. Corals acquire carbon for skeletogenesis directly from
seawater DIC, and indirectly via respiration of both photosynthetically and
heterotrophically acquired carbon [Swart et al., 1996; Grottoli, 1999, 2002; Grottoli and
16
Wellington, 1999; Grottoli et al., 2006]. Environmental parameters such as cloud cover
and light availability influence the value of skeletal δ13C whereby as light intensity
decreases, photosynthesis decreases and coral skeletal δ13C decreases [Fairbanks and
Dodge, 1979; Cole and Fairbanks, 1990; Klein et al., 1992; Carriquiry et al., 1994;
Grottoli, 1999, 2002; Grottoli and Wellington, 1999; Reynaud-Vaganay et al., 2001;
Heikoop et al., 2002; Ferrier-Pages et al., 2003]. Skeletal δ13C has also been shown to
decrease with increasing water depth and is likely also driven by light attenuation with
increased depth [Land et al., 1975; Carriquiry et al., 1994; Grottoli, 1999, 2002;
Reynaud-Vaganay et al., 2001; Ferrier-Pages et al., 2003] as well as increases in
heterotrophy [Porter, 1976; Muscatine et al., 1989, Palardy et al., 2005]. In shallowwater corals, such as those found on coastal coral reefs in Puerto Rico, the majority of the
carbon in coral skeletons is likely derived indirectly via photosynthesis, and a smaller
portion of skeletal carbon being derived directly from seawater DIC [Grottoli and
Wellington, 1999; Furla et al., 2000; Grottoli, 2002, Cohen and McConnaughey, 2003].
Thus, significant changes in the background δ13C of seawater DIC should be reflected in
the skeletal δ13C signal of the corals, over and above seasonal changes in light levels.
Radiocarbon values in coral skeletons have been shown to closely reflect the Δ14C
of seawater DIC in which they are growing [Druffel and Linick, 1978; Nozaki et al.,
1978; Konishi et al., 1982], independent of the metabolic effects associated with δ13C.
Coral skeletal Δ14C measurements have thus far proved useful for tracing the history of
water mass movement and circulation in subtropical and tropical oceans [Druffel, 1987;
Toggweiler et al., 1991; Guilderson and Schrag, 1998; Druffel et al., 2001] and
determining the natural variability of oceanic surface water reservoir ages [Guilderson et
17
al., 2005]. In this study, coral skeletal Δ14C measurements will be used to help
differentiate land-use and metabolically driven changes in the δ13C signature of the coral
records. If older DIC (depleted in Δ14C) is being transported to the coastal ocean and
inundating reef corals during periods of increased river discharge, then the Δ14C within
the coral skeleton should also become depleted in Δ14C. Since riverine DIC is depleted in
both δ13C and Δ14C relative to the open ocean and Δ14C in coral skeletons is only affected
by changes in seawater Δ14C, the influence of terrestrial DIC in coral skeletons should be
evidenced as synchronous anomalous depletions in both coral skeletal δ13C and Δ14C.
Trace Elements in Coral Skeletons
Other elements with identical charges and similar ionic radii can substitute for
Ca2+ (ionic radius: 1.12 Å) during skeletogenesis [see review by Sinclair, 1999],
including Ba2+ (1.42 Å) and Sr2+ (1.26 Å). Equation 1.3 gives the general chemistry of
such ionic substitutions, using Ba as and example:
Ba2+ (aq) + HCO3- (aq) Ù BaCO3 (s) + H+ (aq)
(Equation 1.3)
Such elemental substitutions are common during the building of CaCO3 skeletons by
many marine organisms, including corals, and the process is dictated by a number of
environmental and biological factors. These factors include: the chemical composition of
the surrounding seawater [Sinclair, 1999; Alibert et al., 2003; Lewis et al., 2007], the
ambient temperature of the seawater in which the organism grows [Shen et al., 1996;
Fallon et al., 1999; Marshall and McCulloch, 2002], and biological and thermodynamic
18
effects [Cohen et al., 2002; Marshall and McCulloch, 2002; Cohen and McConnaughey,
2003; Sinclair et al., 2005].
Trace element ratios relative to Ca in coral skeletons are commonly used as
proxies for environmental changes in the ocean over annual to multi-decadal time periods
[Shen and Sanford, 1990, Sinclair, 1999]. For example, secular changes in coral skeletal
Ba/Ca [Lea et al., 1989], Mn/Ca [Shen et al., 1992], Cd/Ca [Shen et al., 1987] and Pb/Ca
[Shen and Boyle, 1987] have been used to investigate environmental parameters such as
upwelling, El Niño Southern Oscillation (ENSO), and industrial contamination. In nearshore non-upwelling environments, elements such as Ba, Mn, and Y have been used to
interpret changes in the influx of terrestrially-derived sediments carried from rivers onto
patch reefs in the Great Barrier Reef (GBR) lagoon [Alibert et al., 2003; McCulloch et al.,
2003; Sinclair and McCulloch, 2004; Lewis et al., 2007]. Of these elements, Ba shows
the most promise as a tracer of river discharge and associated sediment flux [see
McCulloch et al., 2003] because it readily desorbs from suspended particles upon
entering saline waters. Other trace elements such as Mn, Y and the rare earth elements
(REE) exhibit similar estuarine desorption behavior [Hoyle et al., 1984], although records
of these elements in corals have thus far have not been demonstrated to have a high
fidelity with either Ba/Ca or riverine discharge records [e.g. Lewis et al., 2007].
Interpreting Land-Ocean Carbon Flux in Coral Skeletal Geochemistry
In Puerto Rico, corals can be found growing in close proximity to freshwater
inputs and are readily exposed to discharge from adjacent river systems. Since using
paired measurements of both δ13C and ∆14C has been effective for calculating sources,
19
sinks, and residence times of organic matter in temperate rivers, the same dual-isotope
approach is used in this study in order to optimize the information recorded in coral
skeletons. Since corals draw on DIC for calcification, the influence of terrestrial carbon
flux to the coastal ocean should be recorded in coral skeletons. Long-term depletion of
atmospheric δ13C due to the “δ13C Suess effect” (the gradual δ13C depletion of
atmospheric CO2 due to the continued anthropogenic burning of fossil fuels; [Friedli et
al., 1986]; see also [Suess, 1955] for original description of phenomenon in relation to
∆14C) should also be recorded in the coral record. On sub-annual timescales, periods of
sustained peak river discharge events where large volumes of freshwater water inundate
the reef for several days to weeks should result in depletions of δ13C and ∆14C in seawater
DIC. Since seawater DIC is ultimately a source of carbon for calcification in shallowwater corals (whether acquired as photosynthetically fixed carbon [Furla et al., 2000;
Cohen and McConnaughey, 2003], or directly from seawater), the δ13C and ∆14C of the
coral skeleton should record the influx of terrestrially derived DIC as negative anomalies
from the long-term trend. Statistically, values of coral skeletal Δ14C should be positively
correlated with skeletal δ13C values over the chronology of the coral record. For coral
skeletal δ13C, such negative departures should occur over and above the natural
(metabolic) variability of δ13C within the coral skeletal record. Furthermore, these
negative δ13C and ∆14C departures should coincide with the timing of the wet season and
increases in skeletal Ba/Ca.
Since trace elements in coral skeletons can also be used to reconstruct the timing
and magnitude of river discharge and sediment flux in tropical oceans, the potential exists
to combine trace metal and carbon isotope records to produce a multi-proxy record of
20
land-ocean carbon flux. Ba/Ca, Mn/Ca, and Y/Ca in coral skeletons have been used to
interpret changes over time in sediment delivery to the coastal ocean by large rivers in
Australia [McCulloch et al., 2003; Lewis et al., 2006]. Therefore, these trace element
records may be a useful proxy for the history of POC delivery to the coastal ocean. When
trace elements are examined in combination with coral skeletal δ13C and ∆14C, it may be
possible to derive records of fluxes of two major carbon pools (POC and DIC) from
tropical small mountainous rivers to the coastal ocean. If such records are recoverable
from corals, the timing of increased coral skeletal Ba/Ca, Mn/Ca, and Y/Ca is expected to
be coherent with the timing of peak river discharge (wet season) and synchronous
depletions of coral skeletal δ13C and ∆14C anomalies.
RESEARCH PROPOSAL
The research described in the following chapters serves to identify linkages
between carbon transported from land to the tropical coastal ocean via small mountainous
rivers and the geochemical record preserved within the skeletons of corals growing on
reefs near the mouths of those rivers. In the tropics, where small rivers are thought to be a
major contributor to global land-ocean carbon flux, studies have thus far been limited to
the largest of rivers (i.e. the Amazon), and are otherwise rare or non existent. The lack of
information on the transport and delivery of carbon to the ocean in tropical systems
represents a major gap in our understanding of the global carbon cycle. Carbon isotopes
and trace elements archived in the skeletons of corals growing near the mouths of small
tropical rivers may help fill this knowledge gap by providing a history of carbon delivery
to the tropical coastal ocean over the past century. The goals of this research are to: 1)
21
Characterize the carbon isotope signature of forested and agricultural tropical river
catchments and adjacent coastal waters within Puerto Rico; 2) examine a long-term, highresolution record of the carbon isotopes recorded in the skeleton of a coastal coral over
the past half century, and 3) use coral carbon isotopes and trace elements in a multi-proxy
approach to indentify patterns of riverine DIC and POC flux to the coastal ocean as
preserved in coral skeletons.
Design of the Study
River, seawater, and coral core samples were collected at two study areas within
Puerto Rico near the towns of Fajardo and Guanica (Fig. 1.2). These locations were
chosen because each area has coral reefs located in close proximity to river mouths, and
have catchments with different and known precipitation patterns and land-use histories.
The Fajardo study area is located on the northeastern coastal plain of Puerto Rico (Fig.
1.2A), and encompasses the catchment of the major river in the region, the Rio Fajardo.
The Rio Fajardo originates in the Luquillo Mountains and flows seaward in an easterly
direction, emptying into Vieques Sound. The catchment has a drainage area of
approximately 70 km2 and contains several smaller-order streams that feed the main stem
of the Rio Fajardo [Clark and Wilcock, 2000].
Guanica is a primarily agricultural area located in the Lajas Valley on the
southwestern coast of Puerto Rico (Fig. 1.2B), in the rainshadow of the Cordillera Central.
The Rio Loco is the primary river within the Guanica catchment, and drains south into
Guanica Bay. The Rio Loco has been heavily channelized and is partially fed by two
22
Figure 1.2. Map showing the location of the Fajardo (A) and Guanica (B) study areas
within Puerto Rico, and field sampling sites within each study area. Orange dots show the
location of water sampling sites along transect from headwater to reefs at each study area.
Corals were collected at Caho Ahogado in Fajardo and Cayo Coral in Guanica. Base
images are Lansat Thematic Mapper mosaics publicly available at www.nasa.gov.
23
drainage/irrigation canals, Canal Principal de Drenaje Valle de Lajas and Canal Principal
de Riego Valle de Laja. The other major source of water to the Rio Loco is Presado Loco,
a man-made reservoir with an 18 m free crest spillway discharge dam that was
constructed in 1952 [Holmquist et al., 1998]. The reservoir Presado Loco contains a
reservoir volume of 1.3 x 106 m3 and is fed by ephemeral streams originating in the
foothills of the Cordillera Central.
River- and seawater samples were collected in each study area during both peak(rainy season, May-December) and low-flow conditions (dry season, January–April)
along a transect at sites ranging from headwater regions to the coral reefs at each study
area (Fig. 1.2). By sampling during both peak- and low-flow conditions at each site, the
full-range of hydrographic and isotopic measurements could be captured in both river
catchments. At each sampling site within each study area, water samples were collected
for the analysis of total DIC, DOC, and POC concentration and δ13C and Δ14C isotope
values. Duplicate samples were collected at some sites in both study areas in order to
enable quality control of measurements within each season. Water sampling methods
were based on those described in Raymond and Bauer [2001b], and are described in
detail in each of the following chapters. Additional data that were recorded at each
sampling location within each study site included: latitude, longitude, salinity, air
temperature, pH, sampling depth, and turbidity.
Five coral cores, each 3 cm in diameter, were also collected (Puerto Rico DRNA
permit #: 04-C-003) from massive mounding corals growing on nearshore reefs within
each study area. Cores were taken from colonies of the two most abundant massive coral
species (Montastraea faveolata, Siderastrea siderea) at each reef using a hand-held
24
underwater pneumatic drill powered by compressed air. Detailed coral collection,
preparation, geochronology, and geochemical analytical techniques are provided where
appropriate in the chapters that follow.
Chapter 2: Concentrations and carbon isotope (δ13C & Δ14C) geochemistry of DIC,
DOC, and POC in forested and agricultural river catchments and adjacent coastal
waters within Puerto Rico.
The Rio Fajardo catchment is predominantly forested (C3 plant-dominated; δ13C ≈
-26‰), while the Guanica catchment is predominantly agricultural (C4 plant- dominated;
δ13C ≈ -12‰). Isotopically, such differences in standing vegetative cover are known to
change the δ13C signature of soil organic matter [Smith and Epstein, 1971], and should
also affect the δ13C signature of POC, DOC and DIC in the natural waters within and
adjacent to each study area. If this holds true, the δ13C of coastal seawater in each study
area should be isotopically reflective of the differences in land cover, and such
differences should be more pronounced during the wet season when river discharge is
known to be large. Furthermore, the 14C age of organic matter (POC & DOC) in the
Fajardo catchment should be relatively younger (higher Δ14C) than that of the Guanica
catchment due to a decrease in the level of soil disturbance and turnover in the forested
catchment. This signal is also expected to be more pronounced during the rainy season.
Such seasonal and land-use-driven changes in river and seawater chemistry should
ultimately be measurable in the carbon isotopes (δ13C and Δ14C) for the individual carbon
pools (POC, DOC, DIC) in the natural waters of each river catchment. Therefore, the
following hypotheses (stated in the form of the first alternative with the null being the
hypothesis of no difference) can be tested:
25
H1: Riverine DIC, DOC, and POC δ13C and values are lower and ∆14C
values are higher (younger) in water samples from reforested
catchments (Fajardo) than in samples from agricultural catchments
(Guanica).
H2: Seawater DIC-, DOC-, and POC-δ13C and -∆14C values are both lower in
coastal waters during the wet season compared to the dry season.
In order to test H1 and H2, wet and dry season δ13C and Δ14C values of riverine and
seawater DIC, DOC and POC values will be compared using a two-way analysis of
variance (ANOVA) with season and location evaluated as fixed effects. Significant
differences between the locations will indicate expected differences in the character of
carbon in forested versus agricultural catchments, while differences between seasons will
indicate a seasonal control for the delivery of carbon to the coastal ocean. In addition, the
concentration of all carbon pools (DIC, DOC, and POC) will be reported and used to
calculate internal sources and sinks of carbon and to make seasonal estimates of carbon
export flux to the coastal ocean. Isotopic data will be used similarly to generate seasonal
isotopic land-ocean mixing curves for each study area.
Chapter 3: Coral Skeletal Dual Carbon Isotope (δ13C and Δ14C) Record of the Delivery
of Terrestrial Carbon to the Coastal Waters of Puerto Rico
The research presented in Chapter 3 examines the nature of both the sub-annual
and long-term variability of carbon isotopes (δ13C and Δ14C) within a coral skeleton
26
growing near the mouth of the Rio Fajardo. Information gained on the concentration and
isotopic character of carbon delivered to the coastal ocean by tropical rivers presented in
Chapter 2 sets the stage for interpreting the coral record. Fajardo was chosen for this
analysis due to the close proximity (~1 km) of a coral reef to the mouth of the Rio
Fajardo, and the fact that it is the only study area where river discharge data exist over the
same time span covered by the isotope chronology of the coral skeleton (~60 years). In
Chapter 3, the following hypotheses (stated in the form of the first alternative with the
null being the hypothesis of no difference) are tested:
H1: River discharge and coral skeletal δ13C values are coherent and
inversely correlated on annual timescales.
H2: Coral skeletal δ13C and ∆14C are positively correlated.
H3: δ13C and ∆14C of riverine and seawater DIC are postitively correlated.
Cross-spectral analysis of coral δ13C values and Rio Fajardo discharge data are used to
test H1. Calculation of the Pearson product-moment correlation between coral skeletal
δ13C and Δ14C are used to test H2 and H3. The carbon isotopes within the coral skeleton
were expected to exhibit a significant positive correlation, which reflects the same or a
similar relationship found between δ13C and Δ14C of riverine and seawater DIC as
described by H3. Depletions in δ13C and Δ14C were expected to occur nearly
synchronously within the coral skeletal record if terrestrially-derived DIC was indeed
influencing the isotope signature observed within the coral skeleton.
27
Chapter 4: Coral Skeletal Carbon Isotopes (δ13C & Δ14C) and Trace Element Ratios
(Ba/Ca, Mn/Ca, Y/Ca) Record Freshwater Input to the Tropical Coastal Ocean.
Since the trace element Ba, and to a lesser extent Mn and Y, in coral skeletons can
be used to reconstruct the timing and magnitude of river discharge and sediment flux in
tropical oceans, the potential exists to combine the trace metal records with carbon
isotope records to produce a multi-proxy record of land-ocean carbon flux. The coastal
zone of the Fajardo study area is a shallow non-upwelling environment, where the
dominant source of trace elements to the coastal ocean is delivery by rivers. Thus corals
growing near the mouth of the Rio Fajardo should record river discharge events as peaks
in Ba, Mn and Y in their skeletal records. These elements are measureable in coral
skeletons at high temporal resolution using laser ablation inductively coupled plasma
mass spectrometry (LA-ICP-MS). When used in combination with carbon isotopic
records (δ13C and Δ14C), as presented in Chapter 3, trace elements may help elucidate a
more complete picture of land-ocean carbon (and total sediment) flux to tropical oceans.
In light of this, the following hypotheses (stated in the form of the first alternative with
the null being the hypothesis of no difference) are tested in Chapter 4:
H1: Coral Ba/Ca, Mn/Ca, and Y/Ca are annually coherent and positively
correlated with river discharge in the Rio Fajardo catchment.
H2: Coral Ba/Ca, Mn/Ca, and Y/Ca are annually coherent and inversely
correlated with coral skeletal δ13C.
28
In order to test H1, cross-spectral analysis was be performed between each of the coral
trace element records (Ba/Ca, Mn/Ca, and Y/Ca) and between each individual trace
element record and Rio Fajardo discharge data. It was expected that the three trace metal
records would be coherent with each other over the chronology of the Fajardo coral
record. Ba/Ca was expected to be strongly coherent and in-phase with river discharge.
Similarly, spectral analysis was used to examine the relationship between the three trace
element records (Ba/Ca, Mn/Ca, and Y/Ca) and coral skeletal δ13C as a means to test H2.
If the coral trace element records were indeed coherent with river discharge records, they
were expected to also be coherent with coral skeletal δ13C. However in this relationship,
coral skeletal δ13C was expected to decrease with increases in the trace elemental ratios
due to the influx of isotopically lighter DI- δ13C bathing the coral during times of
increased river discharge, as inferred from variations in the trace element ratios of the
coral skeleton.
BROADER IMPACTS
This work elucidates the important role small tropical rivers play in the local carbon cycle
in tropical coastal environments by linking the carbon budgets of tropical terrestrial and
marine environments. This study provides the first comprehensive analysis of land-ocean
carbon flux in the tropics, and presents data critical to understanding the importance of
small tropical river systems to global carbon cycling in the context of global climate
change. As part of a larger collaborative effort, this work improves the understanding of
the fate and interconnection of carbon entering small mountainous tropical rivers and
discharging into coastal marine environments by identifying a measurable link preserved
29
and recorded in coral skeletons. This first quantitative analysis of terrestrial DIC record
preserved in the δ13C and Δ14C record of coral skeletons lays the foundation for the
development of a fully quantitative proxy of the delivery of terrestrial DIC to the coastal
ocean. Multi-proxy records incorporating both carbon isotopes and trace elements also
provide a foundation for quantifying two major sources of carbon to the coastal ocean
(DIC and POC). Such proxies would be invaluable for many other areas of the tropics
where river discharge data are few, and local carbon cycling is not well understood. This
information could be used to gain a clearer understanding of historical dynamics in
tropical land-ocean carbon flux in the context of modern global climate change.
Information gleaned from this study has been shared with local scientists, fisherman and
resource managers within Puerto Rico, all of whom have been actively involved in the
field sampling portion of this research.
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42
CHAPTER 2
CARBON ISOTOPE GEOCHEMISTRY OF TWO TROPICAL SMALL
MOUNTAINOUS RIVER CATCHMENTS AND ADJACENT COASTAL
WATERS IN PUERTO RICO
Ryan P. Moyer1, Andréa G. Grottoli1, and James E. Bauer2
1)
The Ohio State University, School of Earth Sciences,
125 South Oval Mall, Columbus, OH 43201 USA
2)
Virginia Institute of Marine Science, College of William and Mary
Route 1208, Gloucester Point, VA 23062 USA
Chapter 2 is formatted as a manuscript intended for submission to the journal Global
Biogeochemical Cycles, published by the American Geophysical Union.
Keywords: dissolved inorganic carbon; dissolved organic carbon; particulate organic
carbon; δ13C; Δ14C; Tropical small mountainous rivers.
43
ABSTRACT
Tropical small mountainous rivers (SMRs) may transport up to one third of the
total carbon (C) delivered to the world’s oceans. Additionally, land-use change in the
tropics has altered C cycling both on land and in rivers and directly impacts the transfer
of C from land to the coastal ocean. The quantity and isotopic character of C delivered to
the ocean by SMRs is poorly quantified, yet is a critical component of the global C cycle.
This study presents a seasonal dual isotope (13C & 14C) characterization of the three
major C pools in one forested and one agricultural river catchment and their adjacent
coastal waters within Puerto Rico. The riverine concentration of dissolved inorganic C
(DIC) was significantly higher in the agricultural catchment. Dissolved and particulate
organic C (DOC and POC, respectively) concentrations were highly variable with respect
to study area and season. The oxidation of organic matter (OM) contributed to the
riverine DIC pool in both catchments, however DIC was modern but DOC and POC
exported to the coastal ocean were highly aged. The oldest riverine DOC was strongly
influenced by aged effluent of irrigation drainage in the agricultural catchment. During
times of peak river discharge organic C in coastal waters was more reflective of terrestrial
sources, indicating that tropical SMRs may transport unaltered organic carbon to the
coastal ocean when discharge is high. In the forested catchment land-ocean C flux was
regulated by seasonal river discharge, and hence precipitation. This study represents a
first-order comprehensive analysis of the concentration and isotopic character of the three
major C pools transported to the coastal ocean via tropical SMRs. The organic C pools in
tropical exhibited high variability of concentration and isotopic character between
44
catchment, season, and sampling year, and indicate that both land-use and river discharge
are important in controlling C flux in tropical SMRs.
45
INTRODUCTION
The flux of inorganic and organic forms of carbon from rivers to the coastal ocean
is an important component of the global carbon budget [Hedges, 1992; Sigenthaler and
Sarmiento, 1993; Benner, 2004; Sabine et al. 2004]. The quantities and isotopic character
of different forms of terrestrially derived carbon to the coastal ocean, and their impact on
the global carbon cycle, are only beginning to be understood at local scales due to a small,
but growing body of reliable river, estuarine, and seawater carbon geochemical
measurements. Most studies have focused on large temperate rivers and the few
measurements from the tropics are largely restricted to recent studies of the Amazon.
Small tropical rivers may transport as much as 40% of the total terrestrial carbon
delivered to the coastal ocean [e.g. Milliman and Syvitski, 1992; Milliman et al., 1999;
Lyons et al., 2002], yet the quantity and character of the carbon being delivered to the
coastal ocean is relatively unknown. In addition, land-use change in the tropics has
dramatically altered carbon cycling both on land [Houghton et al., 2000] and in rivers
[Mayorga et al., 2005]. The lack of information on the quantity and character of carbon
delivered to the ocean by small tropical river systems represents a major gap in our
understanding of the global carbon cycle.
Rivers in general are sites of intense soil organic matter (OM) input, transport and
processing, thus influencing the abundance, composition, and timing of carbon
discharged to the coastal ocean. Soil OM may age significantly on land or within river
basins prior to mobilization by rivers and estuaries [Kao and Liu, 1996; Cole and Caraco,
2001; Masiello and Druffel, 2001; Raymond and Bauer, 2001a,b; Blair et al., 2003].
Prior to or during mobilization in rivers, a portion of the terrestrial organic carbon pool is
46
converted to dissolved organic carbon (DOC) [Hope et al., 1994; Aitkenhead-Peterson et
al., 2003, 2005]. A significant portion of this riverine DOC pool becomes highly
bioavailable and is readily degraded through numerous biogeochemical pathways,
including: sorption-desorption [Hedges and Keil, 1999], microbial utilization [Coffin et
al., 1993; Moran et al., 1999; Zweifel, 1999; Raymond and Bauer, 2000; McAllister et al.,
2006], photo-oxidation [Mopper et al., 1991; Amon and Benner, 1996; Moran et al., 2000;
Mopper and Kieber, 2002; McCallister et al., 2005], and respiration [Smith and
Hollibaugh, 1997; Hopkinson et al., 1999; Cai, 2003]. As a result of these processes, a
large fraction of DOC is ultimately converted to dissolved inorganic carbon (DIC) by the
time it reaches the river mouth [Miller and Zepp, 1995; Raymond et al., 2000; Opsahl
and Zepp, 2001; Raymond and Bauer, 2001a,c; Mayorga et al., 2005]. Estuarine mixing
also plays an important role in the degradation and cycling of DOC, and a significant
portion of carbon transported to estuarine waters is altered before reaching the coastal
ocean [Raymond and Bauer, 2001a,c; Wang et al., 2004].
Particulate organic carbon (POC) is also transported to the coastal ocean via rivers,
and can be more abundant than DOC [Meybeck, 1982; Alexander et al., 1998; Carey et
al., 2005]. Small mountainous rivers, including those in tropical systems, have been
found to have the oldest POC [Kao and Liu, 1996; Komada et al., 2004, 2005] and
sediment OM deposits [Blair et al., 2003; Leithold et al., 2006] observed in river systems
globally. Anthropogenic influences such as land-use change and river dam construction
have also greatly influenced the distribution of particulate matter in river systems. In
altered systems, POC concentration generally increases with distance downstream due to
47
increased runoff caused by anthropogenic practices [Milliman and Meade, 1982; Meade,
1996].
The riverine delivery of these organic carbon pools to the coastal ocean represents
a substantial component of the organic carbon cycle [Hedges, 1992]. This riverine flux
alone is sufficient enough to support the entire turnover of organic carbon in the ocean
[Williams and Druffel, 1987; Bauer et al., 1992; Druffel et al., 1992]. However, despite
the large input of terrestrially derived organic carbon to the ocean, the quantities of DOC
and POC measured in seawater and marine sediments typically do not correspond to
those inputs [Hedges et al., 1992; Opsahl and Benner, 1997; Wang et al., 2004].
Evidence from carbon isotopes (δ13C and Δ14C) has shown little terrestrial imprint on the
isotopic composition of the organic carbon pools in the ocean. However, since tropical
small mountainous rivers (SMRs) deliver significant amounts of organic carbon to the
coastal ocean and have shorter residence times than larger river systems, the quantities
and isotopic character of terrestrial carbon pools delivered to the coastal ocean may be
more reflective of a terrestrial carbon source. If true, the delivery of carbon to the coastal
ocean via tropical SMRs may be a significant component of the global carbon cycle that
is currently unaccounted for in most models.
Information on both δ13C and Δ14C in the DIC, DOC and POC of river and
estuarine waters has been especially effective for determining sources, sinks, and
residence times of carbon and has been shown to be more effective than using either
isotope alone in both temperate [Masiello and Druffel, 2001; Raymond and Bauer,
2001a,b; Blair et al., 2003; Nagao et al., 2005] and tropical [Mayorga et al., 2005] river
systems. The research presented herein provides seasonal δ13C and Δ14C measurements
48
and estimates of land-ocean carbon flux for DIC, DOC, and POC in two tropical SMR
catchments and their adjacent coastal waters within Puerto Rico. The goals of this study
were: 1) to identify potential sources and sinks of carbon exported to the coastal ocean
from two tropical SMR catchments with different land-use histories, 2) calculate the
potential fluxes of carbon from land to the coastal ocean in two tropical SMR catchments,
and 3) identify estuarine and coastal processes that may influence the ultimate isotopic
character of carbon entering the coastal ocean from land via tropical SMRs. The reported
findings represent the first comprehensive carbon isotope analysis of the three major
carbon pools transported to the coastal ocean via tropical SMRs. Such information is
critical to understanding the importance of tropical SMRs to both local and global carbon
cycling in the context of present and future global climate change.
METHODS
Study Areas
Two study areas were chosen within Puerto Rico near the towns of Fajardo and
Guanica (Fig. 2.1). The Guanica study area is located in the Lajas Valley on the
southwestern coast of Puerto Rico (Fig. 2.1A). and is primarily drained by two man-made
irrigation and drainage canals, Canal Principal de Drenaje Valle de Lajas and Canal
Principal de Riego Valle de Laja, which join to form the Rio Loco a few kilometers north
of the Bahia de Guanica. In 1952 Presado Loco, a reservoir with an 18 m free-crest
spillway discharge dam, was constructed further upstream within the Rio Loco catchment
[Holmquist et al., 1998]. Presado Loco contains a reservoir volume of 1.3 million m3, and
is the main source of the remaining natural stem of the Rio Loco. At its headwaters, the
49
Rio Loco drains igneous and metamorphic (serpentenite) rocks, while the lowland Rio
Loco and associated irrigation canals drain consolidated alluvium and limestone bedrock
[Monroe, 1980]. The Guanica study area is located in the orographic rainshadow of the
Cordillera Central, and receives an average of 860 mm yr-1 rainfall [Lugo et al., 1978]. In
Guanica rainfall is most abundant during the wet season which occurs from May through
December, and significantly less rainfall occurs during the dry season (January through
April). Therefore, the Presado Loco reservoir and Lajas irrigation canals typically only
receive water from feeder streams during the wet season and after heavy rains. Present
land cover in the Guanica study area consists of 60% dry cropland and pasture, 33%
wooded wetland, 5% needle-leaf forests, 2% grassland (pasture), and 0.2% unclassified
lands [USGS, 2001]. The Guanica study area represents an opposing end-member system
to the Fajardo study area. Guanica is situated directly in the rainshadow of the Cordillera
Central and the region receives the lowest annual precipitation of any area in Puerto Rico.
Despite this reduced precipitation, the Lajas Valley is considered a “breadbasket” region
of Puerto Rico as a result of the extensive irrigation, and the majority of the Rio Loco
catchment is agricultural land dominated by both C3 (soybeans) and C4 (corn and sugar)
plants.
The Fajardo study area is located on the northeastern coastal plain of Puerto Rico
(Fig. 2.1B), and the primary river is the Rio Fajardo. The Rio Fajardo originates in the
Luquillo Mountains and flows seaward in an easterly direction, emptying into Vieques
Sound in eastern Puerto Rico. The Rio Fajardo is fed by several smaller-order mountain
streams and the catchment occupies an area of ~70 km2. At its headwaters, the Rio
Fajardo drains steep bedrock valleys, while the downstream portion of the river drains
50
recent alluvium to the head of a coastal plain, where stream flow is tidally influenced
[Clark and Wilcock, 2000]. The Fajardo catchment receives an average of 1591.5 mm
rainfall per year, with peak precipitation occurring in the months of May, October,
November. The Rio Fajardo catchment has experienced more reforestation than the
Guanica study area, and present land cover consists of 45.6% partly developed or
abandoned lands, 30.1% cropland and pasture, 8.4% evergreen forest, 6.5% lowland
forest, 4.0% developed land, and 3.8% savanna [USGS, 2001]. The Fajardo study area
represents an end-member system with respect to both precipitation and present land-use.
The catchment is fed by streams originating in the Sierra de Luquillo, which receive the
highest annual precipitation of any area in Puerto Rico, and the majority of the catchment
is forested and dominated by C3 plants.
Precipitation over insular Puerto Rico exhibits seasonal variability within each
year, with most areas experiencing a wet season during the months of June through midJanuary, and a dry season from mid-January through May [Calvesbert, 1970]. Despite the
seasonal variability, the island does receive precipitation in every month of the year, and
average annual rainfall across the entire island is 1,750 mm yr-1 [Schneidermann et al.,
1976]. However, due to the pronounced orographic effect, the Sierra de Luquillo in the
northeast receive over 4,000 mm yr-1 of rainfall while the southwestern regions of the
island receive as little as ~500 mm yr-1 [Lugo and Garcia-Martino, 1996]. Thus, the
Guanica and Fajardo study areas represent two tropical SMR catchments with very
different land-use and precipitation patterns. Guanica is predominantly agricultural and
receives less annual precipitation, while Fajardo is largely forest and abandoned pasture
and receives significantly more annual precipitation. The inclusion of both study areas
51
provides the opportunity to compare the quantities and isotopic character of major carbon
pools in two very different tropical SMR systems.
Field Sampling
River, estuary, and seawater samples were collected during both the wet (October
2004, 2007) and dry seasons, (March 2005, 2008) along a transect extending from inland
to the coastal ocean in each study area (Fig. 2.1). In 2004 and 2005, water samples were
collected at four locations along the transect, including: 1) up-river (inland), 2) at the
river mouth, 3) a station located a median distance between the river mouth and a nearby
coral reef, and 4) directly overlying a nearby coral reef. In 2007 and 2008 an additional
sampling site was added in the low salinity coastal waters adjacent to the river mouth at
each study area. In March 2008 the headwaters of each river in each study area were
sampled.
Detailed water sample collection methods are described in Raymond and Bauer
[2001b]. Briefly, sub-surface (0.3 – 1.5 m below the surface) water samples were
collected with a peristaltic pump equipped with 10% HCl-rinsed silicone tubing and
filtered using pre-baked (500º C) Whatman QMA quartz fiber filters (0.7 μm nominal
pore size). DIC samples were stored in pre-cleaned (10% HCl, baked at 500º C) glass
serum bottles and poisoned with mercuric chloride. DIC samples were kept in the dark
and stored at room temperature. Filtered DOC samples were stored in pre-cleaned (10%
HCl) polycarbonate bottles and, along with POC samples, kept on ice in the field and
immediately transferred to a -20º C freezer upon return to the lab. The filters containing
the POC samples were individually stored in pre-baked (500º C) aluminum foil, sealed in
52
a plastic bag, and stored frozen at -20º C. Duplicate samples were collected each season
at inland and reef sites within each study area. Latitude, longitude, salinity, pH, water
temperature, water transparency, and the volume of water passed through each filter were
recorded at each sampling site within each study area.
Sample preparation & concentration measurements
DIC samples were prepared for isotopic analyses using methods similar to those
described by Kroopnick [1974]. Briefly, each sample was acidified with 85% orthophosphoric acid, sparged under ultra-high purity (UHP) helium flow, and the resulting
CO2 cryogenically purified under vacuum. The resultant CO2 gas was then split into two
glass ampoules: one for δ13C (the per-mil deviation of 13C:12C relative to the Vienna Pee
Dee Belemnite standard) and one for Δ14C (the per mil deviation of 14C:12C relative to the
95% Oxalic Acid-1 standard) analyses. DIC concentrations were obtained from the
pressure-volume relationship of a calibrated section of the vacuum line. The accuracy of
these measurements was tested against trials where known volumes of CO2 were injected
into the vacuum line and subjected to the same cryogenic purification methods prior to
making the concentration measurements. The average precision of these repeated trials (n
= 8) was < 1.0%.
The methods used in the preparation and isotopic analysis of DOC samples are
reviewed in detail by Raymond and Bauer [2001b], and a brief description is given here.
For DOC samples collected in 2007 and 2008, 100 ml of sample water was placed in a
quartz reaction vessel directly connected with a gas extraction vacuum line. Samples
were acidified to a pH of ~2 using high-purity 85% H3PO4 and sparged with UHP N2 gas
53
in order to remove all DIC. Samples were then saturated with UHP O2 gas and irradiated
for 2 hours with a medium-pressure 2400 W Ultraviolet fluorescent lamp (Hanovia Co.).
The CO2 produced from the oxidation of DOC was purged from the reaction vessel using
UHP N2 gas and passed through a KIO3 trap to remove any chlorine and bromine
produced from seawater salts. The CO2 was then cryogenically purified on the vacuum
line and split into glass ampoules, one for δ13C and one for Δ14C analyses. The
concentration of DOC in all samples (2004 – 2008) was measured using a Shimadzu
TOC-5000A Pt-catalyzed high-temperature analyzer using a four-point calibration curve
with glucose as a standard. HP water blanks were run after every 10 samples to ensure
that carryover between samples was negligible. The average standard deviation of all
replicate [DOC] analyses (n = 18) was 8.1 μM.
POC samples were collected in duplicate at each sampling site within each study
area. For POC samples collected in 2007 and 2008, one filter of each duplicate was used
for radiocarbon analysis. All POC samples were fumed with HCl vapor using methods
similar to those described by Lorrain et al. [2003] in order to remove any inorganic
carbon which may have been deposited on the filter at the time of collection [see also
Hedges and Keil, 1984; Komada et al., 2008]. Each sample was then sealed in a prebaked quartz tube along with pre-baked CuO and Ag metal and combusted at 900º C in
order to produce CO2 gas [Sofer, 1980]. The CO2 resulting from POC oxidation was then
purified on a vacuum line and sealed in a glass ampoule for radiocarbon analysis. POC
content of all filters was measured using a calibrated intensity-weight relationship
obtained from the high-temperature combustion of each sample in a Costech Analytical
54
Elemental Analyzer. These data were reported in μg C, and divided by the volume of
water passed through each filter to obtain an estimate of POC concentration in μg L-1.
δ13C measurements
The δ13C of DIC (DI-δ13C) measurements were made by cracking the CO2 gas
ampoules into a multiport inlet system connected to a Finnigan Delta Plus IV SIR-MS.
Repeated measurements of an internal standard (n = 13) had a standard deviation
≤±0.02‰. Ten percent of all samples were run in duplicate and the standard deviation of
these measurements was ±0.04‰.
The δ13C of DOC (DO-δ13C) samples collected in 2004 and 2005 was measured
using methods described by Osburn and St.-Jean [2007] in which a continuous-flow wetchemical DOC oxidation (WCO) system was interfaced directly to a Finnigan Delta Plus
XP high-amplification isotope ratio mass spectrometer (IRMS). The standard deviation of
repeated measurements of an internal standard was 0.30‰. For samples collected in 2007
and 2008, the of DO-δ13C was measured by cracking the CO2 gas ampoules into a
multiport inlet system connected to a Finnigan Delta Plus IV SIR-MS at The Ohio State
University. Repeated measurements of an internal standard (n = 12) had a standard
deviation of ±0.10‰. Ten percent of all DO-δ13C measurements were made in duplicate,
with a standard deviation of ±0.19‰ for all duplicate measurements. Osburn and St-Jean
[2007] found measured DO-δ13C values of natural water samples to be consistent
between both of the above methods.
HCl-fumed POC samples from each site were combusted in a Costech Analytical
Elemental Analyzer with a high-temperature, sealed-tube, flow-through combustion
55
chamber. The resulting CO2 gas was transferred to a Finnigan Delta IV Plus IRMS via a
Finnigan ConFlow III open split interface for the analysis of the δ13C of POC (PO-δ13C).
Repeated measurements of internal standards (n = 85) had a standard deviations of
±0.14 ‰. At least ten percent of all samples were analyzed in duplicate, and the standard
deviation of these measurements was ±0.06 ‰. All δ13C measurements are reported as a
per mil (‰) deviation of the sample relative to the Vienna Pee Dee belemnite (VPDB)
limestone standard [Coplen, 1996].
Δ14C measurements
For analyses of the ∆14C of DIC (DI-∆14C), ampoules of CO2 gas extracted from
samples collected in 2004 and 2005 were sent to the National Ocean Sciences
Accelerator Mass Spectrometry (AMS) facility at Woods Hole Oceanographic Institute.
Samples collected in 2007 and 2008 were sent to the Arizona AMS Laboratory at the
University of Arizona for analysis. For both sets of samples, CO2 gas was converted to
graphite using H2 gas and Fe as a catalyst and the ratio of 14C/12C was measured via AMS,
with background subtraction applied using 14C-free groundwater. The standard deviation
of DI-∆14C measurements was ±5.0‰
For the analysis of the ∆14C of DOC (DO-∆14C) and POC (PO-∆14C), ampoules of
CO2 gas extracted from samples collected in 2007 and 2008 were sent to the Arizona
AMS Laboratory. For both sets of samples, CO2 gas was converted to graphite using H2
gas and Fe as a catalyst and the ratio of 14C/12C was measured via AMS, with background
subtraction applied using 14C-free groundwater. The standard deviation of all organic
∆14C measurements was ±7.0‰.
56
All radiocarbon measurements were reported by the laboratory as fraction modern
and converted to Δ14C according to the conventions of Stuiver and Polach [1977]. The
Δ14C values reported here were corrected for fractionation using δ13C values measured
via SIR-MS. All Δ14C values are reported as the per mil (‰) deviation of the sample
relative to the 95% Oxalic Acid-1 standard.
Data analysis
A fully factorial model III analysis of variance (ANOVA) was used to test for
differences between study area (Fajardo vs. Guanica), season (wet vs. dry), and salinity
(freshwater vs. marine), and the interaction between each of those factors for each of the
following variables: [DIC], DI-δ13C, DO-Δ14C, [DOC], DO-δ13C, DO-Δ14C, [POC], POδ13C, and PO-Δ14C. Only data from freshwater (salinity ≤ 2‰) and marine end-member
(salinity ≥ 34‰) sites were included in these analyses. A posteriori slice tests [e.g. tests
of simple effects; Winer, 1971] were used to explore significant interaction effects and
Bonferroni corrections were not used [Quinn and Keogh, 2002].
Averaged values are reported as arithmetic means ±1 standard deviation, and
differences were considered statistically significant at p ≤ 0.05. All data sets were
determined to be normally distributed via Lilliefors test for normality [Lilliefors, 1967]
based on the Kolmogorov-Smirnov distribution prior to ANOVA analyses. Except where
indicated, all statistical analyses were conducted using SAS version 9.1.3 of the SAS
System for Windows (© 2000-2004 SAS Institute Inc. SAS and all other SAS Institute
Inc. product or service names are registered trademarks or trademarks of SAS Institute
Inc., Cary, North Carolina, USA.).
57
Conservative mixing curves were calculated for DI-δ13C, DI-Δ14C, DO-δ13C and
DO-Δ14C based on a simple two end-member mixing equation [Spiker, 1980; Raymond
and Bauer, 2001b]:
Is = Fr Ir [X]r + Fm Im [X]m
[X]s
(Equation 2.1)
where Is, Ir and Im are isotope values corresponding to an intermediate salinity, the
riverine end-member, and the marine end-member, respectively. Fr and Fm represent the
riverine and marine fraction which can be calculated based on salinity (Fr + Fm = 1); and
[X]s, [X]r, and [X]m are the concentrations of DIC or DOC at a given salinity, the river
end-member, and the marine end-member, respectively. [X]s can be calculated as a
function of Fr or Fm. Conservative mixing lines were also generated for the concentration
of DIC and DOC by fitting a linear trend between the freshwater and marine end-member
concentrations for each study area.
Net flux of dissolved constituents (DIC and DOC) from rivers to coastal waters
via the associated estuaries in each study area were estimated using mass-balance
equations derived by Kaul and Froelich [1984]. When the actual mixing behavior of
dissolved constituents is continuous and can be described using simple quadratic
equations, the fluxes of those dissolved constituents are defined as:
Riverine flux = Q * Co
(Equation 2.2)
Internal flux = Q (Cs - Co)
(Equation 2.3)
Export flux = Q * Cs
(Equation 2.4)
58
where Q is river discharge (in m3 s-1), Co (μM) is the concentration where the quadratic
equation intersects the y-intercept (i.e. the concentration at zero salinity), and Cs (μM) is
the concentration of the constituent where the tangent at the seawater end-member of the
equation intersects the y-intercept. The riverine flux represents carbon being delivered
through the estuary to the coastal ocean via the river, the internal flux represents carbon
added or removed within the estuary, and export flux represents the net carbon
transported to the coastal ocean through the estuary (riverine + internal flux). In order to
derive the Co and Cs terms, the mixing behavior of each dissolved constituent was
modeled using a best-fit (r2 ≥ 0.98) quadratic equation of the form y = ax2 + bx + c. The
y-intercept (c) of each quadratic equation was used to calculate (Co) and the y-intercept
for the tangent at the seawater end-member (Cs) was calculated from the quadratic
equation using the following equation:
Cs = q - (2ax + b) * y
(Equation 2.5)
It should be noted that these calculations relate to fluvial export fluxes of dissolved
constituents only, and for DIC do not include atmospheric exchanges of CO2. The
majority of internally added and exported DIC is assumed to be in the form of
bicarbonate (HCO3-) and not CO2, the concentration of which represents only a small
fraction (< ~15%) of total DIC at the end-member pH values measured in this study (pH
range = 7.5 – 8.9).
59
RESULTS
Raw data for the concentration and isotopes of DIC, DOC, and POC are given in
Tables 2.1, 2.2, and 2.3, respectively. Below, the effects determined to be significant by
ANOVA statistics for each carbon pool and their isotopes are presented, along with the
mixing behavior and land-ocean fluxes of each carbon pool.
Dissolved inorganic carbon
A posteriori slice tests of the significant interaction effects in the ANOVA
revealed that the dry season concentration of riverine DIC in Guanica was significantly
higher than that of the wet season (Table 2.4; Fig. 2.2A, C) and the dry season marine
DIC concentration (Fig. 2.2C). The concentration of riverine DIC in Guanica during the
dry season was also significantly higher than that of Fajardo during the dry season (Fig.
2.2C, D). In Fajardo, the concentration of DIC was significantly higher at river sites than
at marine sites (Fig. 2.2B, D). In both Guanica and Fajardo, DIC exhibited nearconservative mixing behavior during the 2004 wet season, but mixed non-conservatively
during the 2007 wet season (Fig. 2.2A, B). An estuarine source accounted for the nonconservative mixing in both study areas during the 2007 wet season. During the dry
season in Guanica, all sites were dominated by end-member (freshwater or marine)
salinities, and mixing relationships of DIC or its isotopes could not be wholly determined
(Fig. 2.2C). DIC mixed nearly-conservatively during both 2005 and 2008 in Fajardo (Fig.
2.2D). Export fluxes of DIC were similar in both Guanica and Fajardo during the wet
season (Table 2.5), however the estimation of accurate internal and total export fluxes
was not possible during the dry season in Guanica due to the lack of data from low and
60
mid-salinity waters (Fig. 2.2C) needed to constrain the quadratic mixing models. Average
total DIC export flux in Fajardo was five times higher during the wet season than during
the dry season (Table 2.5).
At both study areas, average freshwater DI-δ13C and DI-Δ14C values were
significantly lower than at marine sites (Table 2.4, Figs. 2.3 & 2.4). In addition,
freshwater DI-Δ14C in Guanica was significantly lower than freshwater DI-Δ14C in
Fajardo during the wet season (Fig. 2.4A, B). In Fajardo, freshwater DI-Δ14C values were
significantly higher during the wet season than during the dry season (Fig. 2.4B, C).
During both the 2004 and 2007 wet seasons, DI-δ13C and DI-Δ14C mixed nonconservatively in Guanica (Figs. 2.3A & 2.4A) and conservatively in Fajardo (Figs. 2.3B
& 2.4B). The non-conservative mixing in Guanica was due to an estuarine source of
enriched DI-δ13C and DI-Δ14C (Figs. 2.3A & 2.4A). During the 2005 dry season, both
DI-δ13C and DI-Δ14C mixed non-conservatively in Fajardo (Figs. 2.3D & 2.4D).
However, during the 2008 dry season DI-δ13C mixed non-conservatively (Fig. 2.3D)
while DI-Δ14C mixed nearly conservatively (Fig. 2.4D). An estuarine source of depleted
DI-δ13C and DI-Δ14C was present in all cases where DI-δ13C and DI-Δ14C mixed nonconservatively during the dry season in Fajardo.
Dissolved organic carbon
The concentration of DOC in both study areas was highly variable among sites,
seasons, and sampling years (Table 2.2, Fig. 2.5). Despite this high variability, a
posteriori slice tests of the significant ANOVA interaction effects (Table 2.4) revealed
that: 1) freshwater DOC concentrations were significantly lower during the wet season
61
than during the dry season in Guanica (Fig. 2.5A, C); 2) the concentration of freshwater
DOC was significantly higher than marine DOC concentration during the dry season in
Guanica (Fig. 2.5C); and 3) the average dry season concentration of riverine DOC was
significantly higher in Gaunica than in Fajardo (Fig. 2.5C, D). Of note, the concentration
of DOC in both Guanica and Fajardo generally increased from river to the coastal ocean
during the wet season in 2004, while the opposite pattern was evident during the 2007
wet season (Fig. 2.5A, B). In both the 2004 and 2007 wet seasons, DOC in Guanica
mixed nearly conservatively (Fig. 2.5A), while in Fajardo DOC exhibited nonconservative mixing behavior (Fig. 2.5B). In 2004 the estuary provided a source of DOC
in Fajardo, while is 2007 the estuary was a sink for DOC (Fig. 2.5B). During the dry
season of both 2005 and 2008 mixing relationships in Guanica could not be determined
based on the distribution of measured salinities (Fig. 2.5C). DOC mixed nonconservatively during both the 2005 and 2008 dry seasons in Fajardo, with the estuary
being a source of higher DOC concentration (Fig. 2.5D). DOC fluxes to the coastal ocean
were generally an order of magnitude lower than corresponding DIC fluxes in both study
areas (Table 2.6). Fajardo had a higher export flux than Guanica during the wet season
(Table 2.6), while lack of low and mid-salinity data in Guanica (Fig. 2.5) prevented direct
comparison of the DOC fluxes between the two study areas during the dry season. In
Fajardo, the average wet season DOC export flux was five times larger than average dry
season export flux (Table 2.6).
The DO-δ13C values in both study sites were also highly variable between sites,
seasons, and sampling years and no statistically significant differences between site,
season, or salinity were detected (Table 2.4; Fig. 2.6). However, there were noteworthy
62
differences in DO-δ13C values between sampling years. In Guanica, DO-δ13C decreased
from river to the coastal ocean and mixed nearly conservatively during the 2004 wet
season (Fig. 2.6A), but the opposite was observed in 2007 (Fig. 2.6A). However, in
Fajardo, non-conservative mixing occurred during both the 2004 and 2007 wet seasons
(Fig. 2.6B). An estuarine source of enriched DO-δ13C was present when non-conservative
mixing occurred during the wet season in both Guanica.(Fig. 2.6A) and Fajardo (Fig.
2.6B). During the dry season in Guanica, all sites were dominated by end-member
(freshwater or marine) salinities, and mixing relationships of DO-δ13C could not be
determined (Fig. 2.6C). DO-δ13C decreased from the river to the ocean during the 2005
dry season in Fajardo and mixed non-conservatively due to an estuarine source of
enriched DO-δ13C, while the opposite was observed during the 2008 dry season (Fig.
2.6D).
DO-Δ14C was only measured during only the 2007 wet and 2008 dry seasons, and
therefore less variability was observed when compared to the variability in DOC
concentration or DO-δ13C (Fig. 2.7). DO-Δ14C decreased from land to the coastal ocean
and mixed non-conservatively during the wet season in both Guanica and Fajardo (Fig.
2.7A, B). In Guanica a source of enriched DO-Δ14C was present in low salinity (<10‰)
waters, while a source of depleted DO-Δ14C was present in mid salinity (10 – 20‰)
waters (Fig. 2.7A). In Fajardo, the non-conservative mixing was due to a source of
depleted DO-Δ14C across all salinities between the river and marine end members (Fig.
2.7B). Mixing behavior of DO-Δ14C could not be determined during the dry season in
Guanica, but DO-Δ14C mixed non-conservatively during the dry season in Fajardo (Fig.
63
2.7C, D). An estuarine source depleted in DO-Δ14C was responsibly for the nonconservative mixing during the dry season in Fajardo (Fig. 2.7D).
Particulate organic carbon
The concentration of POC was highly variable between both freshwater and
marine sites in Guanica (Table 2.3). However in Fajardo, POC concentrations were
generally low at freshwater and marine end member sites, and highest at brackish sites
(Table 2.3). Statistically, no significant differences in POC concentration were detected
between study area, season, or salinity (Table 2.4). PO-δ13C significantly increased from
river to the coastal ocean in both study areas and was significantly lower during the dry
season compared to the wet season (Tables 2.3 & 2.4). In both Guanica and Fajardo,
freshwater PO-δ13C was significantly more enriched during the wet season than during
the dry season (Table 2.4). PO-Δ14C values had highly variability in freshwater and
marine sites at both study areas (Table 2.3) and there were no significant differences
between these values with respect to study area, season, or salinity (Table 2.4).
DISCUSSION
The observed differences in the concentration and isotope data for each the carbon
pools in Guanica and Fajardo (Tables 2.1 – 2.4; Figs. 2.2 – 2.7) are likely being driven by
a complex set of interactions between biological, chemical and geological processes. The
identification of the sources of carbon to rivers has helped constrain the fluxes of carbon
in temperate [Masiello and Druffel, 2001; Raymond and Bauer, 2001c, Raymond and
Hopkinson, 2003, Raymond et al., 2004] and tropical river systems [Mayorga et al.,
64
2005]. The significant differences between Guanica and Fajardo and between wet and dry
season riverine DIC concentration (Fig. 2.2), DI-Δ14C (Fig. 2.4), DOC concentration (Fig.
2.5), and PO-δ13C (Table 2.4) are likely source-driven, and the elucidation of those
carbon sources to the SMRs is necessary to understand the observed differences in the
fluxes of both DIC (Table 2.5) and DOC (Table 2.6) with respect to study area and
season. Therefore, the results are interpreted here in terms of identifying sources of
inorganic and organic carbon to rivers and the coastal ocean that can both explain the
observed statistical patterns in the data and help constrain the calculated fluxes of carbon
to the coastal ocean via SMRs.
Sources of inorganic carbon to tropical SMRs
The primary sources of DIC in most river systems are the oxidation of OM via
both abiotic (e.g. photo-oxidation) and microbial process (e.g. soil and aquatic
respiration), weathering of carbonate and siliciclastic rocks [Telmer and Veizer, 1999],
and to a lesser extent atmospheric CO2. The range of δ13C values associated with each of
each of these sources is given in Figure 2.8. In addition, each of these potential sources
can contribute DIC with highly variable Δ14C values, specific to the age of that source
(Fig. 2.8A). For instance, the oxidation of aged OM produces DIC depleted in Δ14C and
reflective of the age of the OM being oxidized. DIC derived from the bedrock weathering
can have Δ14C values ranging from moderately depleted, if modern CO2 generated from
overlying soil is involved, to highly depleted if carbonate weathering is involved. DIC
derived from the atmosphere or the oxidation of modern OM is enriched in Δ14C.
65
Riverine DIC in both Guanica and Fajardo had δ13C values significantly lower
than that expected from an atmospheric source and suggest that the respiration of OM is a
major source of riverine DIC in both study areas (Fig. 2.8A). In addition, freshwater DIΔ14C values in Guanica were lower than those in Fajardo during the wet season (Fig.
2.4A, B), suggesting that the OM being oxidized to produce DIC was somewhat aged in
Guanica compared to Fajardo. In the dry season the oxidation of modern OM is the
dominant source of DIC in both study areas (Fig. 2.8A). Thus, the sources of DIC in
Guanica are influenced by season, but not in Fajardo. However, the concentrations of
DOC (Table 2.2, Fig. 2.5) and POC (Table 2.6) were not sufficient to account for the
entire DIC pool in either study area. These findings suggest that respired soil CO2 or
atmospheric exchanges must also contribute to riverine DIC in both Guanica and Fajardo,
and that in situ respiration is not the lone source of DIC to either the Rio Loco or the Rio
Fajardo (Fig. 2.8A). Weathering of bedrock can largely be excluded as a primary source
of DIC to either river system since riverine δ13C and Δ14C of DIC did not overlap with the
range of either isotope expected from carbonate rocks (Fig. 2.8A). In addition, although
the DI-δ13C of freshwater DIC did fall within the range of δ13C expected for weathering
via soil CO2, the DI-Δ14C values at all freshwater sites were much younger than would be
expected from old source rock material.
Sources of organic carbon (DOC and POC) to tropical SMRs
The main sources of organic carbon (DOC and POC) to rivers are degraded plant
biomass [Benner, 2004], surface soil organic matter [Hope et al., 1994; Raymond and
Bauer, 2001b,c; Aitkenhead-Peterson et al., 2003, 2005], autochthonous production
66
[Raymond et al., 2004] and sediments eroded from organic-rich bedrock (when
underlying the catchment) [Kao and Liu, 1996; Leithold and Blair, 2001; Masiello and
Druffel, 2001; Leithold et al., 2006]. Organic δ13C values are typically reflective of the
vegetation within a given river catchment. In catchments dominated by C3 plants (most
tropical trees and shrubs) in Puerto Rico, plant-derived organic matter has an average
δ13C of ~ -30‰, and soil organic matter averages ~ -27‰ [von Fischer and Tieszen,
1995]. Catchments dominated by C4 plants (sugarcane, corn, most pasture grasses) have
plant biomass and soil organic matter with average δ13C values of ~ -13‰ [Smith and
Epstein, 1971] and ~ -10‰ [Balesdent et al., 1987], respectively. This isotopic
distinction should be important in Puerto Rico, where much of the island was once
deforested and sugar was the dominant cash crop. The δ13C of autochthonous organic
matter can be predicted from measured DI-δ13C values and assuming a kinetic
fractionation of 20‰ for freshwater primary production [e.g. Chanton and Lewis, 1999],
yielding a DO-δ13C range of -35 to -26‰ in both study areas. Although organic matter
may age on land prior to mobilization in rivers [Blair et al., 2003; Cole and Caraco, 2001;
Kao and Liu, 1996; Masiello and Druffel, 2001; Raymond and Bauer, 2001a], studies
from the Amazon basin have shown tropical soils to have shorter residence times than
temperate soils [Trumbore, 1993]. Shorter residence times coupled with modern inputs
from plant biomass and autochthonous production create a potentially large range of Δ14C
values that can be expected in terrestrially derived organic matter.
The high variability observed in the concentration (Fig. 2.5), and δ13C and Δ14C of
the DOC (Fig. 2.9A) and POC (Fig. 2.10A) pools suggests that freshwater organic carbon
is derived from a combination of sources, and that the majority of those sources are
67
delivering aged OM to the river system (Figs. 2.9A & 2.10A). At most freshwater sites in
both Guanica and Fajardo, δ13C of DOC and POC had values reflective of C3 plants.
Despite a history of island-wide sugar cane production and widespread modern
agriculture in Guanica, only one freshwater DOC (Fig. 2.9A) and one freshwater POC
(Fig. 2.10A) sample had a δ13C value reflective of C4 plants, and these came from the Rio
Fajardo. However the corresponding Δ14C values were modern and therefore not
reflective of the historical land-use in Fajardo. Conversely, the depleted Δ14C values
corresponding to C3 δ13C values in each organic carbon pool were highly depleted and
therefore reflective of an old organic carbon source (i.e. pre-agricultural period terrestrial
OM). Only one site at either study area (Presado Loco, Guanica) had DOC and POC δ13C
and Δ14C values reflective of autochthonous production. This finding is reasonable given
that Presado Loco is a standing body of water with longer residence time than SMRs, and
where lacustrine processes dominate, thereby allowing primary producers to accumulate
in high abundance.
Comparison of SRMs in Puerto Rico to other global river systems
While the ages of the POC collected in both the Rio Loco (Guanica) and the Rio
Fajardo (Fajardo) are consistent with the POC ages of other large temperate and tropical
rivers and temperate SMR systems (Fig. 2.11), the DOC results are unusual compared to
most large tropical, sub-tropical and temperate river systems (Fig. 2.12). The only river
systems with DOC pools as old as those of the Rio Loco are a temperate SMR from
continental North America (Santa Clara River) [Masiello and Druffel, 2001], the Hudson
River [Raymond and Bauer, 2001a], and some large arctic rivers [Neff et al., 2006;
68
Raymond et al., 2006] (Fig. 2.12). Studies of small, high-latitude watersheds have
demonstrated that the Δ14C-depleted riverine DOC pool is due to increased input of DOC
that has interacted with deeper soil profiles containing older OM [Neff et al., 2006]. Thus,
the age of the DOC is primarily controlled by the residence time of soluble soil organic
carbon prior to mobilization by rivers, which is in turn controlled largely by temperature
and precipitation [Raich and Schlesinger, 1992]. The freshwater DOC pool was
sometimes highly aged during both seasons in Guanica (Table 2.2; Figs. 2.7, 2.9, & 2.12),
where average annual precipitation is low. Limited precipitation is likely to increase
residence time of soil OM (SOM) due to lower mobilization rates caused by lack of
precipitation. Furthermore, recent studies have suggested that traditional agricultural
practices increase the export of aged SOM [Fontaine et. al., 2007]. Therefore when SOM
is mobilized in the Guanica study area by large rainfall events, aged SOM is likely the
major source of aged DOC observed in the waters of the Rio Loco. A sample taken from
a subterranean irrigation effluent (Lajas Canal Drainage Ditch site) supports this idea.
This sample had the oldest DOC of any sample collected in either Guanica or Fajardo and
was draining surface soil layers directly below an actively farmed field.
Compared to other tropical or sub-tropical river catchments, such as the Amazon
[Mayorga et al. 2005] or Lanyang Hsi [Kao and Liu, 1996], underlying lithology is not
thought to have been a major source of inorganic or organic carbon in either study area. The
oldest reported POC ages have come from rivers directly eroding organic-rich
sedimentary bedrock (shales) [Kao and Liu, 1996]. The lithology of most of Puerto Rico
is andesitic basalts in the central mountain ranges flanked by sedimentary deposits of
consolidated alluvium and carbonates [Meyerhoff, 1933]. No major occurrences of
69
organic-rich sedimentary rocks have been reported on the island, and hence there is
limited potential for underlying lithology to be a primary source of POC in either study
area.
Sources of carbon to coastal waters
Brackish sites in both Guanica and Fajardo had DI-δ13C values that were more
enriched than freshwater sites, but depleted compared to marine sites (Fig. 2.8B).
Brackish DI-Δ14C was modern in both study areas, indicating a larger influence of
atmospherically derived CO2 in brackish waters, with a smaller contribution of DIC
produced from the oxidation of OM. The DI-δ13C and DI-Δ14C at marine sites in both
study areas is reflective of modern atmospheric CO2 as the major source of marine DIC,
and the influx of these waters to the estuary may also cause the brackish water DIC to be
more reflective of an atmospheric source.
The DOC of brackish water sites had highly variable isotopic signatures,
reflecting a combination of both terrestrial and marine sources (Fig. 2.9B). The brackish
sites with DO-δ13C values closest to marine primary productivity had modern DO-Δ14C
values, while those sites with DO-δ13C values more reflective of terrestrial organic matter
had depleted DO-Δ14C values indicative of older sources of DOC. These findings seem
counter-intuitive considering that marine DOC is usually much more highly aged than
terrestrial DOC [Bauer, 2002]. The two brackish sites with terrestrial DO-δ13C signatures
were both measured at the mouth of the Rio Fajardo, where the catchment receives a
larger amount of annual rainfall than Guanica in both the wet and dry seasons. The
associated higher river discharges in the Fajardo study area (Table 2.6) may be rapidly
70
transporting DOC to the coastal ocean before it can be oxidized or isotopically altered. If
true, such a process would be unique to tropical SMRs, as organic carbon is typically
heavily modified prior to reaching the coastal ocean in large river systems [Raymond and
Bauer, 2000, 2001a,c; Raymond et al., 2004].
The POC of brackish water sites was isotopically indistinguishable from marine
sites in terms of both δ13C and Δ14C (Fig. 2.10B), with the exception of two cases. A wet
season POC sample from an estuarine embayment at the mouth of the Rio Loco in
Guanica (Bahia Noroeste, Fig. 2.1) was reflective of a modern C4 plant source. This
measurement is consistent with both the modern land use within the lower Rio Loco
catchment, and a measurement during the same season at the mouth of the Rio Loco that
had a δ13C signature suggestive of a mixed C3 and C4 plant OM source (Fig. 2.10B).
The δ13C of DOC and POC at marine sites was within the range of organic matter
δ13C reported in other studies of the western Atlantic tropics and sub-tropics [Jeffrey,
1969; Sackett, 1989; Bauer et al., 1992]. The Δ14C of DOC and POC at marine sites was
largely reflective of a refractory organic carbon pool, and was also within the range of
values measured in the sub-tropical western Atlantic [Bauer et al., 1992]. Despite δ13C
falling within the range of natural variability of western Atlantic DOC and POC, both
pools were depleted by an average of ~1‰ relative to the expected range of marine DOδ13C values based on measurements of marine DI-δ13C (Table 2.1) and a marine primary
production fractionation of -19‰ [Lynch-Stieglitz et al., 1995]. This may also indicate
that the stable isotope signature of marine organic carbon pools is being influenced by the
isotopic signature of terrestrially derived DOC. Additionally, the range of ages in both
DOC and POC were nearly the same in terrestrial organic carbon pools as in marine
71
organic carbon pools, suggesting that tropical SMRs may be exporting aged terrestrial
OM directly to the coastal ocean.
Land-ocean carbon flux and estuarine mixing in tropical SMRs
Guanica and Fajardo had similar fluxes of DIC in the wet season despite
discharge of the Rio Loco (Guanica) being nearly 50% of the Rio Fajardo (Table 2.5).
Therefore, the estimated DIC flux in Guanica is likely a result of high riverine DIC
concentrations in the Rio Loco (Fig. 2.2). Due to slower soil flushing rates associated
with lower precipitation in Guanica, respired soil CO2 may have long residence times
[Raich and Schlesinger, 1992] and may therefore contribute large amounts of riverine
DIC upon mobilization. This is consistent with the isotopic evidence for a respired
organic matter source of DIC as discussed above. Additionally, the Rio Loco is fed by a
dammed reservoir (Presado Loco) with a DIC concentration greater than that of any
marine site in either study area. The Fajardo study area receives the highest annual
rainfall of any location within Puerto Rico, so residence times of respired soil CO2 are
expected to be much shorter [Raich and Schlesinger, 1992], thus not allowing for soil
CO2 to accumulate in any great abundance.
DIC added within the estuary at Fajardo accounted for 70% of average wet season
export flux and 60% of average dry season DIC flux (Table 2.5). Studies from temperate
estuarine systems suggest that net heterotrophy and the conversion of CO2 to HCO3balanced by sulfate reduction can result in estuarine additions of DIC [Raymond et al.,
1997, 2000], and such observations have been reported from several temperate estuaries
[Cai and Wang, 1998; Raymond et al., 2000]. The seasonal differences in DIC addition
72
within the Rio Fajardo estuary are consistent with findings from temperate rivers
[Raymond et al., 2000] and suggest that net heterotrophy and sulfate reduction of organic
matter by mangrove sediments could be playing an important role in the estuarine flux of
DIC to the coastal ocean.
The average total export flux of DOC during the wet season was approximately
six times lower in Guanica than in Fajardo. The higher wet season DOC flux in Fajardo is
expected based on higher rates of precipitation and increased mobilization of terrestrial
organic material that occur during the wet season. Previous work in forested catchments
within Puerto Rico has shown riverine concentrations of DOC to be highly dependent
upon discharge, with DOC being most abundant when runoff and discharge are largest
[McDowell and Asbury, 1994]. The average DOC added within the estuary accounted for
78% of the average DOC export flux during both wet and dry seasons in Fajardo, while
estuarine addition only accounted for 31% of the total average DOC export flux during
the wet season in Guanica (Table 2.6). Despite this large difference between Guanica and
Fajardo, these values are consistent with ranges of internal DOC production observed in
temperate river systems (6 – 89%) [Raymond and Bauer, 2001c]. That internal DOC flux
estimates in Fajardo are towards the upper limit of that range suggests that the estuarine
addition of DOC may play an important role in the total export of DOC to the ocean in
Fajardo. This is generally consistent with the high temperatures and greater precipitation
rates in Fajardo, which aid in speeding the decomposition of POC into more soluble
forms. Additionally, Studies from large tropical rivers suggest that intertidal mangroves
and associated sediments can act as sources of DOC [Alongi et al., 1993] and that a large
portion of organic carbon discharged from tropical rivers may originate from mangrove
73
forests [Robertson and Alongi, 1995]. The Rio Fajardo estuary is lined with mangrove
forests which are likely the source of the internal estuarine fluxes of DOC in Fajardo.
Summary
This study represents a first-order comprehensive analysis of the concentration
and isotopic character of the three major carbon pools transported to the coastal ocean via
tropical SMRs. The results suggest that the concentration and isotopic character of the
organic carbon pools (DOC and POC) can be highly variable between study area, season,
and year (Tables 2.2 & 2.3; Figs. 2.5 – 2.7). The results also show that the concentration
and isotopic character of tropical SMRs is highly dependent on the sources of organic
material being transported to the river in individual catchments, and the natural processes
which influence the delivery of this source material to tropical SMRs. For instance, the
Guanica study area had the oldest riverine DOC measured in either study area, and this
was determined to be derived from aged irrigation effluent draining anthropogenically
disturbed agricultural lands. Additionally, single samples from single years can not
effectively capture the range of natural variability of tropical SMRs. Therefore, higher
frequency sampling (~monthly) in consecutive years is likely needed for tropical SMRs,
in order to best constrain the range of natural variability in the quantity, isotopic character,
and flux of terrestrial carbon to the coastal ocean in these systems.
While DIC exported to the coastal ocean was modern, the exported organic
carbon was aged, and the DOC pool in Guanica was older than all but one large
temperate or tropical river where DOC ages have been reported (Fig. 2.12).
Anthropogenic disturbance is largely attributable, where the oldest DOC was measured
74
directly in irrigation drainage effluent waters and at river site downstream of this input of
irrigation effluent in the primarily agricultural Guanica study area. Conversely, the
Fajardo study area which has less agricultural disturbance had younger DOC that was
more reflective of other temperate and tropical river systems (Fig. 2.12). The isotopic
character of organic carbon in riverine, brackish, and marine waters suggested that during
times of increased river discharge, terrestrial carbon may be transported to the coastal
ocean without experiencing intense biogeochemical turnover and alteration in estuarine
waters. Such a finding is rare in comparison to most large tropical [Mayorga et al., 2005]
and temperate [Raymond and Bauer, 2000, 2001a,c; Raymond et al., 2004] river systems.
Acknowledgements: This work was supported primarily by grants to AG Grottoli from
the Andrew W. Mellon Foundation and the National Science Foundation Chemical
Oceanography Program (Grant # 0610487). RP Moyer was partially supported by an
Ohio State University Presidential Fellowship and received additional funding from the
American Association of Petroleum Geologists, the American Geophysical Union, the
Geological Society of America, and the Friends of Orton Hall. We are grateful for field
assistance provided by H Anguerre, M Canals, M Cathey, C Malachowski, C Pacheco
and B Williams. Laboratory analyses were assisted by M Cathey, Y Matsui, and C Paver.
We would like to thank S Levas, A Shinohara, and B Williams for helpful discussions
during the preparation of this manuscript, and A Carey, Y Chin, M Saltzman, and
anonymous persons for their careful reviews and suggestions which improved the overall
quality of the manuscript.
75
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84
TABLES
Site
Guanica – Wet Season
Rio Loco Bridge
Rio Loco Mouth
Bahia Noroeste
Guanica Bay Mouth
Cayo Coral
Guanica – Dry Season
Presado Loco
Rio Loco Upriver
Lajas Canal
Lajas Drainage Ditch
Rio Loco Bridge
Rio Loco Mouth
Bahia Noroeste
Guanica Bay Mouth
Cayo Coral
Fajardo – Wet Season
Fajardo Bridge
Fajardo Mouth FW
Fajardo Mouth SW
Fajardo Bay
Cayo Ahogado
Fajardo – Dry Season
Mt. Britton Trail
Fajardo Upriver
Fajardo Mouth FW
Fajardo Mouth SW
Fajardo Bay
Cayo Ahogado
Date
[DIC]
(μmol/Kg)
Salinity
DI-δ13C
(‰)
DI-Δ14C
(‰)
14
C age
(ybp)
26 Sep 04
22 Oct 07
23 Oct 07
27 Sep 04
23 Oct 07
27 Sep 04
23 Oct 07
27 Sep 04
23 Oct 07
0.0
0.0
5.0
12.0
15.0
35.0
34.0
35.0
36.0
1955
652
1375
2176
2074
1983
952
1980
1297
-10.37
-11.79
-3.76
-3.55
-1.12
0.28
0.68
0.89
1.18
6.1
20.7
55.0
46.4
66.1
56.4
67.9
53.3
59.6
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
21 Mar 08
21 Mar 08
21 Mar 08
21 Mar 08
1 Mar 05
7 Mar 08
8 Mar 08
1 Mar 05
8 Mar 08
1 Mar 05
8 Mar 08
1 Mar 05
8 Mar 08
0.1
0.1
0.4
0.0
0.0
1.8
35.2
35.0
36.1
34.0
36.0
37.0
36.3
2535
2601
2946
3882
5072
3646
2336
2221
2062
1819
1841
2119
1110
-11.16
-12.61
-9.78
-10.59
-10.72
-11.31
-1.80
-0.19
0.01
0.23
0.02
1.21
0.03
16.6
15.5
31.1
9.2
44.7
23.3
61.7
62.5
64.4
67.4
67.0
78.7
70.7
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
6 Oct 04
24 Oct 07
6 Oct 04
24 Oct 07
24 Oct 07
7 Oct 04
24 Oct 07
7 Oct 04
24 Oct 07
0.0
0.0
8.0
2.0
17.0
36.0
26.0
34.5
36.0
641
390
1425
1263
1504
2014
1878
2040
1779
-8.76
-9.82
-3.34
-8.24
0.03
0.66
0.87
0.71
0.92
59.4
49.8
59.2
46.2
67.8
71.2
70.9
78.3
73.9
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
22 Mar 08
20 Mar 08
19 Mar 08
12 Mar 05
19 Mar 08
19 Mar 08
12 Mar 05
19 Mar 08
12 Mar 05
19 Mar 08
0.0
0.0
0.1
17.0
11.1
35.8
36.0
36.1
38.0
36.0
238
620
494
1644
995
2004
2101
1938
2117
1342
-12.16
-10.40
-9.02
-6.34
-6.20
0.62
0.89
0.91
0.93
0.86
80.7
75.1
27.4
20.6
40.3
62.9
65.1
71.6
70.7
68.1
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Table 2.1. Riverine and seawater dissolved inorganic carbon (DIC) data.
85
Site
Guanica – Wet Season
Rio Loco Bridge
Rio Loco Mouth
Bahia Noroeste
Guanica Bay Mouth
Cayo Coral
Guanica – Dry Season
Presado Loco
Rio Loco Upriver
Lajas Canal
Lajas Drainage Ditch
Rio Loco Bridge
Rio Loco Mouth
Bahia Noroeste
Guanica Bay Mouth
Cayo Coral
Fajardo – Wet Season
Fajardo Bridge
Fajardo Mouth FW
Fajardo Mouth SW
Fajardo Bay
Cayo Ahogado
Fajardo – Dry Season
Mt. Britton Trail
Fajardo Upriver
Fajardo Bridge
Fajardo Mouth FW
Fajardo Mouth SW
Fajardo Bay
Cayo Ahogado
Date
[DOC]
(μM)
Salinity
DO-δ13C
(‰)
DO-Δ14C
(‰)
14
C age
(ybp)
26 Sep 04
22 Oct 07
23 Oct 07
27 Sep 04
23 Oct 07
27 Sep 04
23 Oct 07
27 Sep 04
23 Oct 07
0.0
0.0
5.0
12.0
15.0
35.0
34.0
35.0
36.0
173
249
168
231
196
165
94
238
82
-24.14
-27.05
-25.40
-25.35
-24.70
-22.72
-21.60
-27.17
-21.50
-6.0
-208.0
-89.5
---309.5
---266.4
---257.5
9 ±58
1884 ±56
754 ±71
--2976 ±53
--2490 ±56
--2393 ±50
21 Mar 08
21 Mar 08
21 Mar 08
21 Mar 08
1 Mar 05
7 Mar 08
8 Mar 08
1 Mar 05
8 Mar 08
1 Mar 05
8 Mar 08
1 Mar 05
8 Mar 08
0.1
0.1
0.4
0.0
0.0
1.8
35.2
35.0
36.1
34.0
36.0
37.0
36.3
113
129
337
712
203
444
133
102
90
126
78
80
63
-32.00
-29.20
-26.90
-25.30
-23.64
-23.40
-22.30
-22.93
-21.00
-22.81
-21.20
-23.20
-20.90
32.8
27.6
15.8
-257.7
-195.8
-4.4
-103.4
-139.7
-136.5
---199.4
---201.0
Modern
Modern
Modern
2340 ±38
1696 ±76
7 ±56
824 ±62
1155 ±78
1123 ±77
--1733 ±84
--1750 ±70
6 Oct 04
24 Oct 07
6 Oct 04
24 Oct 07
24 Oct 07
7 Oct 04
24 Oct 07
7 Oct 04
24 Oct 07
0.0
0.0
8.0
2.0
17.0
36.0
26.0
34.5
36.0
95
202
301
160
106
130
96
110
82
-24.56
-26.60
-22.70
-24.90
-21.40
-23.39
-21.60
-21.89
-21.80
---22.7
---190.4
-175.7
---204.7
---236.8
--185 ±66
--1707 ±55
1553 ±56
--1841 ±58
--2176 ±54
22 Mar 08
20 Mar 08
12 Mar 05
19 Mar 08
12 Mar 05
19 Mar 08
19 Mar 08
12 Mar 05
19 Mar 08
12 Mar 05
19 Mar 08
0.0
0.0
0.0
0.1
17.0
11.1
35.8
36.0
36.1
38.0
36.0
67
57
71
95
172
153
66
120
56
119
65
-25.80
-29.30
-19.34
-25.80
-21.17
-25.30
-21.40
-26.89
-21.50
-25.19
-21.50
43.0
12.8
-39.7
-61.6
-20.0
-137.3
-204.1
---247.5
---221.5
Modern
Modern
272 ±65
457 ±71
108 ±51
1133 ±55
1780 ±70
--2231 ±76
--1958 ±71
Table 2.2. Riverine and seawater dissolved organic carbon (DOC) data.
86
Site
Guanica – Wet Season
Rio Loco Bridge
Rio Loco Mouth
Bahia Noroeste
Guanica Bay Mouth
Cayo Coral
Guanica – Dry Season
Presado Loco
Rio Loco Upriver
Lajas Canal
Lajas Drainage Ditch
Rio Loco Bridge
Rio Loco Mouth
Bahia Noroeste
Guanica Bay Mouth
Cayo Coral
Fajardo – Wet Season
Fajardo Bridge
Fajardo Mouth FW
Fajardo Mouth SW
Fajardo Bay
Cayo Ahogado
Fajardo – Dry Season
Mt. Britton Trail
Fajardo Upriver
Fajardo Bridge
Fajardo Mouth FW
Fajardo Mouth SW
Fajardo Bay
Cayo Ahogado
Date
POC
(μg/l)
Salinity
PO-δ13C
(‰)
PO-Δ14C
(‰)
14
C age
(ybp)
26 Sep 04
22 Oct 07
23 Oct 07
27 Sep 04
23 Oct 07
27 Sep 04
23 Oct 07
27 Sep 04
23 Oct 07
0.0
0.0
5.0
12.0
15.0
35.0
34.0
35.0
36.0
172
3328
897
77
2448
64
126
12
42
-24.70
-26.42
-20.03
-23.29
-14.80
-20.77
-18.94
-19.42
-17.65
---91.6
-97.5
--45.81
--21.8
---194.7
--718 ±44
771 ±44
--Modern
--Modern
--1686 ±258
21 Mar 08
21 Mar 08
21 Mar 08
21 Mar 08
1 Mar 05
7 Mar 08
8 Mar 08
1 Mar 05
8 Mar 08
1 Mar 05
8 Mar 08
1 Mar 05
8 Mar 08
0.1
0.1
0.4
0.0
0.0
1.8
35.2
35.0
36.1
34.0
36.0
37.0
36.3
364
--711
--868
169
1514
2155
901
315
245
20
10
-37.86
-29.08
-25.73
-28.70
-27.23
-32.44
-21.64
-16.66
-18.27
-17.39
-21.86
-20.26
-19.57
-----13.1
-67.8
---12.9
-35.8
--22.9
--1.9
--26.7
----52 ±48
510 ±51
--51 ±40
240 ±50
--Modern
--Modern
--Modern
6 Oct 04
24 Oct 07
6 Oct 04
24 Oct 07
24 Oct 07
7 Oct 04
24 Oct 07
7 Oct 04
24 Oct 07
0.0
0.0
8.0
2.0
17.0
36.0
26.0
34.5
36.0
19
289
813
976
3157
114
1007
60
107
-24.72
-25.17
-18.17
-22.19
-20.59
-20.02
-18.85
-19.72
-20.81
---35.9
---30.9
-12.9
--28.8
---68.6
--240 ±50
--199 ±41
51 ±40
--Modern
--517 ±60
22 Mar 08
20 Mar 08
12 Mar 05
19 Mar 08
12 Mar 05
19 Mar 08
19 Mar 08
12 Mar 05
19 Mar 08
12 Mar 05
19 Mar 08
0.0
0.0
0.0
0.1
17.0
11.1
35.8
36.0
36.1
38.0
36.0
254
--225
70
1316
623
812
202
165
95
89
-28.48
-26.37
-26.77
-26.77
-20.36
-21.81
-22.09
-21.08
-22.87
-19.77
-20.71
20.6
16.6
-------10.0
-19.9
---20.9
---5.0
Modern
Modern
------27 ±48
108 ±49
--116 ±57
--7 ±48
Table 2.3. Riverine and seawater particulate organic carbon (POC) data.
87
88
7
1
1
1
1
1
1
1
7
1
1
1
1
1
1
1
7
1
1
1
1
1
1
1
df
F
p
Source
DOC
2.01E7 13.01 <0.001 Model
5.75E6 26.06 <0.001 Area
3.65E6 16.53 <0.001 Season
5582.77 0.03 0.875 Salinity
5.72E6 25.89 <0.001 Area*Season
8.16E6 36.93 <0.001 Area*Salinity
2.22E6 10.06 0.004 Season*Salinity
3.46E6 15.67 <0.001 Area*Season*Salinity
DO-δ13C
602.05 28.10 <0.001 Model
7.74 2.53 0.126 Area
7.06 2.31 0.143 Season
578.83189.15 <0.001 Salinity
1.92 0.63 0.436 Area*Season
2.64 0.86 0.363 Area*Salinity
2.93 0.96 0.339 Season*Salinity
0.06 0.02 0.891 Area*Season*Salinity
DO-Δ14C
7800.32 12.10 <0.001 Model
485.19 5.27 0.032 Area
134.43 1.46 0.239 Season
6413.53 69.64 <0.001 Salinity
925.98 10.05 0.004 Area*Season
6.94 0.08 0.786 Area*Salinity
178.51 1.94 0.178 Season*Salinity
132.88 1.44 0.243 Area*Season*Salinity
SS
7
1
1
1
1
1
1
1
7
1
1
1
1
1
1
1
7
1
1
1
1
1
1
1
df
F
1.33
0.20
1.92
2.85
0.41
0.46
1.48
0.50
8.49E4 2.37
0.19 0.00
7951.97 1.55
7.01E4 13.67
387.00 0.08
1970.27 0.38
975.52 0.19
5691.65 1.11
37.42
0.81
7.69
11.44
1.63
1.84
5.96
2.01
1.25E5 4.88
3.49E4 9.52
1018.24 0.28
5.14E4 14.05
1.70E4 4.65
1.59E4 4.33
3315.56 0.90
2.69E4 7.35
SS
Source
df
SS
F
p
POC
0.002 Model
7 4.97E6 1.44 0.238
0.005 Area
1 1.21E6 2.47 0.130
0.603 Season
1 8.76E4 0.18 0.678
0.001 Salinity
1 8.86E5 1.80 0.193
0.042 Area*Season
1 2135.58 0.00 0.948
0.049 Area*Salinity
1 3.09E5 0.63 0.436
0.352 Season*Salinity
1 1.89E6 3.85 0.062
0.013 Area*Season*Salinity 1 4.54E5 0.92 0.347
PO-δ13C
0.282 Model
7 269.13 8.26<0.001
0.657 Area
1
0.68 0.15 0.706
0.180 Season
1
53.89 11.58 0.003
0.106 Salinity
1 207.57 44.58<0.001
0.530 Area*Season
1
0.38 0.08 0.778
0.505 Area*Salinity
1
20.27 4.35 0.049
0.236 Season*Salinity
1
32.43 6.97 0.015
0.487 Area*Season*Salinity 1
3.23 0.69 0.414
14
PO-Δ C
0.091 Model
7 2.12E4 1.08 0.444
0.995 Area
1 1322.10 0.41 0.542
0.237 Season
1 1.07E4 3.30 0.107
0.003 Salinity
1
68.40 0.02 0.888
0.788 Area*Season
1 658.60 0.20 0.665
0.547 Area*Salinity
1 749.96 0.23 0.644
0.671 Season*Salinity
1
33.83 0.01 0.921
0.313 Area*Season*Salinity 0
-------
p
88
Table 2.4. Results of a fully factorial model III analysis of variance (ANOVA) for dissolved inorganic (DIC), dissolved organic
(DOC), and particulate organic carbon (POC) concentrations, and stable (δ13C) and radiocarbon (Δ14C) data. df = degrees of
freedom. SS = sum of squares. F = calculated F statistic. p = probability. Sources of variability are significant when p ≤ 0.05.
Source
DIC
Model
Area
Season
Salinity
Area*Season
Area*Salinity
Season*Salinity
Area*Season*Salinity
DI-δ13C
Model
Area
Season
Salinity
Area*Season
Area*Salinity
Season*Salinity
Area*Season*Salinity
DI-Δ14C
Model
Area
Season
Salinity
Area*Season
Area*Salinity
Season*Salinity
Area*Season*Salinity
89
Avg.
±SD
Avg.
±SD
Dry
Wet
Avg.
±SD
Avg.
±SD
Dry
Season
Wet
March 2005
March 2008
Oct. 2004
Oct. 2007
March 2005
March 2008
Date
Sept. 2004
Oct. 2007
Q
(m3 s-1)
0.62
0.85
0.74
±0.16
1.42
0.93
1.18
±0.34
0.96
±0.33
1.33
1.59
1.46
±0.18
0.27
0.59
0.43
±0.23
0.95
±0.62
Estuarine
[DIC]
(μmol
Kg-1)
2176
1375
1776
±567
------------1425
1263
1344
±114
1644
995
1320
±459
1332
±273
Marine
[DIC]
(μmol
Kg-1)
1983
2074
2029
±65
1819
2062
1940
±172
1985
±118
2014
1878
1946
±96
2101
2004
2052
±69
1999
±91
Co
(μmol
Kg-1)
1955
699
1327
±889
------------643
716
679
±52
692
500
596
±136
638
±97
Cs
(μmol
Kg-1)
2895
5878
4387
±2109
------------3415
1331
2373
±1474
1832
1113
1473
±509
1923
±1040
Cs - Co
(μmol
Kg-1)
940
5179
3059
±2998
------------2773
616
1.18
±0.34
1140
612
1.18
±0.34
1.18
±0.34
Riverine
Flux (109
μmol d-1)
105.3
51.3
78.3
±38.2
------------74.0
98.1
86.0
±17.1
16.1
25.7
20.9
±6.8
53.5
±39.1
Internal
Flux (109
μmol d-1)
50.6
380.3
215.5
±233.1
------------318.9
84.4
201.7
±165.9
26.5
31.5
29.0
±3.5
115.3
±138.3
Export
Flux (109
μmol d-1)
155.9
431.6
293.8
±195.0
------------392.9
182.5
287.7
±148.8
42.6
57.2
49.9
±10.3
168.8
±162.1
89
Table 2.5. Estimated fluxes of dissolved inorganic carbon (DIC) from land to the coastal ocean in Puerto Rico. Riverine flux is
defined as the product of river discharge (Q) and Co, internal flux is Q(Cs-Co), and export flux is Q * Cs (see Methods &
Materials for complete description). River discharge data were obtained from http://pr.water.usgs.gov/.
Avg.
±SD
Avg.
±SD
Fajardo
Study
Area
Guanica
Riverine
[DIC]
(μmol
Kg-1)
1955
652
1303
±922
5072
3646
4359
±1008
2831
±1933
641
390
515
±177
692
494
593
±140
554
±138
90
Avg.
±SD
Avg.
±SD
Dry
Wet
Avg.
±SD
Avg.
±SD
Dry
Season
Wet
March 2005
March 2008
Oct. 2004
Oct. 2007
March 2005
March 2008
Date
Sept. 2004
Oct. 2007
Q
(m3 s-1)
0.62
0.85
0.74
±0.16
1.42
0.93
1.18
±0.34
0.96
±0.33
1.33
1.59
1.46
±0.18
0.27
0.59
0.43
±0.23
0.95
±0.62
Estuarine
[DOC]
(μmol L1
)
231
168
200
±45
------------301
160
231
±100
172
153
163
±13
197
±70
Marine
[DOC]
(μmol
L-1)
165
196
180
±22
126
90
108
±26
144
±46
130
106
118
±17
120
66
93
±38
105
±28
Co
(μmol
L-1)
173
225
199
±37
------------99
188
144
±63
71
94
83
±16
113
±51
Cs
(μmol
L-1)
351
252
302
±70
------------1254
157
706
±775
357
421
389
±45
547
±484
Cs - Co
(μmol
L-1)
178
27
102
±107
------------1154
-31
562
±838
286
327
306
±29
434
±506
Riverine
Flux (108
μmol d-1)
93.1
165.4
129.2
±51.1
------------114.4
257.8
186.1
±101.4
16.5
48.3
32.4
±22.5
109.3
±107.1
Internal
Flux (108
μmol d-1)
95.9
19.7
57.8
±53.9
------------1328.1
-42.0
643.0
±968.8
66.5
168.1
117.3
±71.8
380.1
±637.7
Export
Flux (108
μmol d-1)
189.0
185.1
187.0
±2.8
------------1442.5
215.8
829.1
±867.4
83.0
216.4
149.7
±94.3
489.4
±638.5
90
Table 2.6. Estimated fluxes of dissolved organic carbon (DOC) from land to the coastal ocean in Puerto Rico. Riverine flux is
defined as the product of river discharge (Q) and Co, internal flux is Q(Cs-Co), and export flux is Q * Cs (see Methods &
Materials for complete description). River discharge data were obtained from http://pr.water.usgs.gov/.
Avg.
±SD
Avg.
±SD
Fajardo
Study
Area
Guanica
Riverine
[DOC]
(μmol
L-1)
173
249
211
±54
203
444
323
±170
267
±122
95
202
148
±76
71
95
83
±17
116
±59
FIGURES
Figure 2.1. Landsat 7 images showing the location of study areas (insets) and sampling
sites within Puerto Rico. A) Fajardo study area and sampling sites (orange dots). B)
Guanica Study area and sampling sites (orange dots). Landsat images available from
www.nasa.gov.
91
5000
A
B
C
D
4000
3000
[DIC] (μmol Kg-1)
2000
1000
0
5000
4000
3000
2000
1000
0
0
10
20
30
40 0
10
20
30
40
Salinity
Figure 2.2. Seasonal dissolved inorganic carbon (DIC) concentration vs. salinity plots for
Guanica and Fajardo. A) Guanica wet season (● = 2004, ● = 2007), B) Fajardo wet
season (● = 2004, ● = 2007), C) Guanica dry season (○ = 2005, ○ = 2008), D) Fajardo
dry season (○ = 2005, ○ = 2008). Dashed lines indicate theoretical conservative mixing
relationships of DIC from rivers to the coastal ocean.
92
2
0
A
B
C
D
-2
-4
-6
DI-δ13C (‰)
-8
-10
-12
2
0
-2
-4
-6
-8
-10
-12
0
10
20
30
40 0
10
20
30
Salinity
Figure 2.3. Seasonal dissolved inorganic carbon stable isotopes (DI-δ13C) vs. salinity
plots for Guanica and Fajardo. A) Guanica wet season (● = 2004, ● = 2007), B) Fajardo
wet season (● = 2004, ● = 2007), C) Guanica dry season (○ = 2005, ○ = 2008), D)
Fajardo dry season (○ = 2005, ○ = 2008). Dashed lines indicate theoretical conservative
mixing relationships of DI-δ13C from rivers to the coastal ocean.
93
40
100
A
B
C
D
80
60
DI-Δ14C (‰)
40
20
0
100
80
60
40
20
0
0
10
20
30
40 0
10
20
30
Salinity
Figure 2.4. Seasonal dissolved inorganic carbon radiocarbon isotopes (DI-Δ14C) vs.
salinity plots for Guanica and Fajardo. A) Guanica wet season (● = 2004, ● = 2007), B)
Fajardo wet season (● = 2004, ● = 2007), C) Guanica dry season (○ = 2005, ○ = 2008),
D) Fajardo dry season (○ = 2005, ○ = 2008). Dashed lines indicate theoretical
conservative mixing relationships of DI-Δ14C from rivers to the coastal ocean.
94
40
500
A
B
C
D
400
300
-1
[DOC] (μmol L )
200
100
0
500
400
300
200
100
0
0
10
20
30
40 0
10
20
30
40
Salinity
Figure 2.5. Seasonal dissolved organic carbon (DOC) concentration vs. salinity plots for
Guanica and Fajardo. A) Guanica wet season (● = 2004, ● = 2007), B) Fajardo wet
season (● = 2004, ● = 2007), C) Guanica dry season (○ = 2005, ○ = 2008), D) Fajardo
dry season (○ = 2005, ○ = 2008). Dashed lines indicate theoretical conservative mixing
relationships of DOC from rivers to the coastal ocean.
95
-18
A
B
C
D
-20
-22
-24
13
DO-δ C (‰)
-26
-28
-30
-18
-20
-22
-24
-26
-28
-30
0
10
20
30
40 0
10
20
30
40
Salinity
Figure 2.6. Seasonal dissolved organic carbon stable isotopes (DO-δ13C) vs. salinity
plots for Guanica and Fajardo. A) Guanica wet season (● = 2004, ● = 2007), B) Fajardo
wet season (● = 2004, ● = 2007), C) Guanica dry season (○ = 2005, ○ = 2008), D)
Fajardo dry season (○ = 2005, ○ = 2008). Dashed lines indicate theoretical conservative
mixing relationships of DO-δ13C from rivers to the coastal ocean.
96
0
-50
A
B
C
D
-100
-150
-200
DO-Δ14C (‰)
-250
-300
-350
0
-50
-100
-150
-200
-250
0
10
20
30
40 0
10
20
30
40
Salinity
Figure 2.7. Seasonal dissolved organic carbon radiocarbon isotopes (DO-Δ14C) vs.
salinity. A) Guanica wet season 2007 (●), B) Fajardo wet season 2007(●), C) Guanica
dry season 2008 (○), and D) Fajardo dry season 2008 (○) Dashed lines indicate
theoretical conservative mixing relationships of DO-Δ14C from rivers to the coastal ocean.
97
100
A
Equil.
Atmos.
CO2
80
60
14
Riverine DOC & POC
20
0
-20
-40
0
200
400
Silicate weathering
-1000
100
C age (ybp)
DI-Δ14C (‰)
40
B
Carbonate weathering
Equil. Atmos.CO2
Riverine DIC
80
60
B
S it
es
0
0
-20
200
-40
C age (ybp)
20
h
k is
rac
14
DI-Δ14C (‰)
40
400
Carbonate rocks & sediments
-1000
-20
-15
-10
-5
0
5
DI-δ13C (‰)
Figure 2.8. Carbon isotope (δ13C and Δ14C) source diagram for A) Freshwater, and B)
brackish and marine dissolved inorganic carbon (DIC). Boxes represent typical ranges of
DI-δ13C and Δ14C for potential sources of DIC. ● = Guanica Wet Season, ○ = Guanica
Dry Season, ● = Fajardo Wet Season, ○ = Fajardo Dry Season, DOC = dissolved organic
carbon, POC = particulate organic carbon, Equil atmos = equilibrated atmospheric.
98
200
A
Freshwater PP
C3 Plants
C4 Plants
0
Ag. Soil
Pre-Ag. Soil
-200
2
3
C age (kybp)
1
14
DO-Δ14C (‰)
0
4
-400
5
-600
200
6
7
B
Marine PP
0
0
-200
2
Rio Loco DOC
3
C age (kybp)
1
14
DO-Δ14C (‰)
Rio Fajardo DOC
4
-400
5
6
7
-600
-35
-30
-25
-20
-15
13
DO-δ C (‰)
Figure 2.9. Carbon isotope (δ13C and Δ14C) source diagram for dissolved organic carbon
(DOC). A) Freshwater DOC and B) brackish and marine DOC. Boxes represent typical
ranges of DO-δ13C and Δ14C for some potential sources of DOC. ● = Guanica Wet
Season, ○ = Guanica Dry Season, ● = Fajardo Wet Season, ○ = Fajardo Dry Season, PP =
primary productivity
99
200
A
Freshwater PP C3 Plants
C4 Plants
Ag. Soils
0
14
1
-200
2
C age (kybp)
PO-Δ14C (‰)
0
3
Pre-Ag. Soils
4
-400
5
200
B
Marine PP
C3 Plants
C4 Plants
0
14
Rio Loco POC
1
Rio Fajardo POC
-200
2
C age (kybp)
PO-Δ14C (‰)
0
3
4
-400
5
-40
-30
-20
-10
13
PO-δ C (‰)
Figure 2.10. Carbon isotope (δ13C and Δ14C) source diagram for particulate organic
carbon (POC). A) Freshwater samples and B) brackish and marine samples. Boxes
represent typical ranges of δ13C and Δ14C for some potential sources of POC. ● =
Guanica Wet Season, ○ = Guanica Dry Season, ● = Fajardo Wet Season, ○ = Fajardo
Dry Season, Ag. = agricultural PP = primary productivity.
100
Figure 2.11. Radiocarbon ages of riverine POC reported in this study (circles) and from
other tropical/sub-tropical (triangles), temperate small mountainous (squares), and large
temperate (diamonds) rivers. Trop = tropical, Ag. = agricultural, SMR = small
mountainous rivers, Lg. = large.
101
Figure 2.12. Radiocarbon ages of riverine DOC reported in this study (circles) and from
other tropical/sub-tropical (triangles), temperate (squares), and arctic (diamonds) rivers.
Trop = tropical, Ag. = agricultural, SMR = small mountainous rivers, Lg. = large, Temp.
= temperate.
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CHAPTER 3
CORAL SKELETAL DUAL CARBON ISOTOPE (δ13C & Δ14C) RECORD OF
THE DELIVERY OF TERRESTRIAL CARBON TO THE COASTAL WATERS
OF PUERTO RICO
Ryan P. Moyer and Andréa G. Grottoli
School of Earth Sciences, The Ohio State University,
125 South Oval Mall, Columbus, OH 43201 USA
Chapter 3 is intended for submission to Limnology and Oceanography, the journal of the
American Society for Limnology and Oceanography. However to achieve consistency
throughout this dissertation, Chapter 3 is formatted in the style of an American
Geophysical Union journal.
Keywords: Coral geochemistry, δ13C, Δ14C, dissolved inorganic carbon, Puerto Rico,
land-ocean carbon flux
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ABSTRACT
Tropical small mountainous rivers may contribute up to 33% of total terrestrial carbon
input to the world’s oceans. However, this flux remains poorly quantified and few
historical records of land-ocean carbon transfer exist for any region on Earth. Corals have
the potential to provide such records in the tropics because they are long-lived, draw on
dissolved inorganic carbon (DIC) for calcification, and isotopic variations within their
skeletons are useful proxies of palaeoceanographic variability. In temperate systems, the
stable- (δ13C) and radiocarbon (Δ14C) isotopes of coastal DIC are influenced by the δ13C
and Δ14C of the DIC transported from adjacent rivers. A similar pattern should exist in
tropical coastal DIC and coral skeletons. Here, a 56-year record of paired coral skeletal
δ13C and Δ14C measurements is presented from a Montastraea faveolata colony growing
~1 km from the mouth of the Rio Fajardo in eastern Puerto Rico. Additionally, δ13C and
Δ14C measurements of the DIC of riverine and adjacent coastal waters were made during
two wet and dry seasons. Three major findings were observed: 1) Synchronous
depletions of both δ13C and Δ14C in the coral skeleton are annually coherent with the
timing of peak river discharge, 2) Riverine DIC was always more depleted in δ13C and
Δ14C than seawater DIC, and 3) and the correlation of δ13C and Δ14C was the same in
both coral skeleton and the DIC of the river and coastal waters. These results suggest that
coral skeletal δ13C and Δ14C are recording the delivery of riverine DIC to the coastal
ocean. Thus, coral records could be used to develop proxies of historical land-ocean
carbon flux for many tropical regions where local carbon cycling is not well understood.
Such information would be invaluable to understanding the role of tropical land-ocean
carbon flux in the context of global climate change.
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INTRODUCTION
The transfer of terrestrially derived carbon from land to the coastal ocean is an
important, but poorly quantified, component of the global carbon cycle. Small
mountainous rivers are thought to be major sources of terrestrial carbon input to the
world’s oceans [e.g. Milliman and Syvitski, 1992]. In the tropics, such rivers may
contribute as much as one third of the total carbon exported to the coastal ocean, yet there
are no data available for most of these rivers in the topical Pacific Ocean [Lyons et al.,
2002], or Caribbean Sea region. More attention has been given to large temperate river
systems where studies show that the stable- (δ13C) and radiocarbon (Δ14C) isotope values
of the coastal seawater dissolved inorganic carbon (DIC) is influenced by the δ13C and
Δ14C of the dissolved and particulate organic carbon being transported from the adjacent
river catchment. Since most studies have been conducted within the last 20 years, very
few multi-decadal, or longer, records of land-ocean carbon delivery are available for any
region of the Earth. Corals have the potential to provide such records in the tropics
because they are long-lived (300+ years), draw on seawater DIC for calcification, and
isotopic variations within their skeletons serve as useful proxy records of
palaeoceanographic variability [See reviews by Druffel, 1997; Gagan et al., 2000;
Grottoli, 2001; Eakin and Grottoli, 2006; Grottoli and Eakin, 2007]. Additionally, corals
growing in near-shore environments record terrestrial processes, such as increased river
discharge and sediment delivery, in their skeletons as fluctuations of elemental barium
[McCulloch et al., 2003] or other trace elements [Lewis et al., 2007].
The δ13C and Δ14C records preserved in the skeletons of corals growing near
rivers may provide a natural archive of the transfer of carbon from land to the coastal
105
ocean. Corals acquire the carbon necessary for skeletogenesis both directly from the DIC
in seawater, and indirectly via respiration of photosynthetically- and heterotrophicallyacquired carbon [Grottoli and Wellington, 1999; Furla et al., 2000; Grottoli, 2002;
Cohen and McConnaughey, 2003; Grottoli et al., 2006]. Coral skeletal δ13C values have
been shown to be regulated by both metabolic and kinetic fractionation effects
[McConnaughey, 1989a,b; Cohen and McConnaughey, 2003]. In most shallow-water
hermatypic corals, skeletal δ13C is largely influenced by metabolic fractionation due to
changes in photosynthesis (light) and heterotrophic rates of carbon acquisition [Swart,
1983; Muscatine et al., 1989; Grottoli and Wellington, 1999; Grottoli, 2002; Swart et al.,
2005]. Environmental parameters such as cloud cover and light intensity have been
shown to influence the value of skeletal δ13C, where as light intensity decreases, both
photosynthesis and coral skeletal δ13C decrease [Fairbanks and Dodge, 1979; Klein et al.,
1992; Grottoli and Wellington, 1999; Heikoop et al., 2000; Reynaud-Vaganay et al.,
2001; Grottoli, 2002]. Skeletal δ13C also decreases with increasing water depth, with the
suggested drivers being a coupling of light attenuation with increased depth as well as
increases in heterotrophy [Muscatine et al., 1989; Grottoli, 1999; Palardy et al., 2005].
Since DIC is a direct source of skeletal carbon, significant changes in the δ13C of
ambient seawater DIC should also be reflected in the skeletal δ13C of coral skeletons,
over and above metabolically-driven variations in skeletal δ13C brought about by changes
in light intensity (photosynthesis) or heterotrophy. The DIC of riverine waters is typically
more depleted in δ13C than seawater, and thus the input of riverine DIC to the coastal
ocean is capable of causing anomalous depletions of δ13C in coastal seawater DIC and
coral skeletons. However, due to the seasonal nature and often coincident occurrence of
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both physical processes which influence the δ13C of seawater DIC, and metabolic process
influencing coral skeletal δ13C, the use of δ13C in coral skeletons as a singular tracer of
changes in ambient seawater DIC has remained difficult [Swart et al., 1996].
Radiocarbon (14C) is a radioactive carbon isotope that is produced naturally in the
atmosphere by the continuous bombardment of 14N atoms with neutrons, and has a halflife of 5730 years. 14C enters the ocean through gas exchange of atmospheric CO2 and has
an equilibration time of 7–10 years, yielding an approximate steady state value in the
atmosphere and ocean over decadal or longer time periods. In the 1950s and 1960s,
thermonuclear weapons testing added a large amount of 14C into the atmosphere,
approximately doubling the “pre-bomb” amount in the atmosphere. Radiocarbon values
in coral skeletons have been shown to closely reflect the 14C composition of the seawater
DIC in which they are growing [Druffel and Linick, 1978; Nozaki et al., 1978; Konishi et
al., 1982], independent of metabolic effects. The DIC of soil pore water and rivers is
largely derived from the respiration and photo-oxidation of aged terrestrial organic matter,
and is therefore more depleted in Δ14C than seawater [e.g. Chasar et al., 2000; Mayorga
et al., 2005]. The input of riverine DIC to the coastal ocean is then also capable of
causing anomalous depletions of Δ14C in coastal seawater DIC and coral skeletons.
Information gained from using paired measurements of both δ13C and Δ14C in
terrestrial and marine aquatic systems has been especially effective for calculating
sources, sinks, and residence times of carbon, and has been shown to be more effective
than using either isotope alone in both temperate [Raymond and Bauer, 2001a,b] and
large tropical [Mayorga et al., 2005] river systems. The goal of this study was to use
paired δ13C and Δ14C measurements in tropical rivers, the coastal ocean, and coral
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skeletons in order to show linkages between riverine DIC and the coral skeleton. Using
this approach, the following three hypotheses were addressed. (1) The influx of Δ14Cdepleted riverine DIC to the coastal ocean should result in anomalous depletions in coral
skeletal Δ14C. (2) Since riverine DIC is depleted in both δ13C and Δ14C relative to the
open ocean and Δ14C in coral skeletons is only affected by changes in seawater Δ14C, the
input of terrestrial DIC to the coastal ocean should be evidenced as synchronous
depletions in both δ13C and Δ14C in coral skeletons. (3) Since terrestrially derived DIC
only influences the waters bathing coral reefs during periods of large river discharge (i.e.
the wet season), depletions in coral skeletal δ13C and Δ14C are only expected to occur
synchronously with peak river discharge. The elucidation of such an isotopic “landsignal” in coral skeletons could provide historical records of terrestrial river discharge
and land-ocean carbon flux in the tropics where such records are scarce or entirely
absent.
MATERIALS & METHODS
Study area
The Fajardo river catchment is located in northeastern Puerto Rico (Fig. 3.1) and
encompasses a total area of ~ 70 Km2. In the early 1900’s nearly all (~93%) of the
catchment was deforested and used for agriculture, with sugarcane being the dominant
crop. Abandonment of agricultural practices and gradual reforestation over the past
century has led to the present land cover which consists of 46% partially developed or
abandoned lands, 30% cropland and pasture, 9% evergreen forest, 7% lowland forest, 4%
developed land, and 4% savanna [USGS, 2001]. The climate in this region of Puerto Rico
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exhibits seasonal variability with a wet season during the months of May through midJanuary, and a dry season during the months of mid-January through April [Calvesbert,
1970]. The catchment receives an average of 1592 mm rainfall per year, with peak
precipitation occurring in the months of May, October, November and peak river
discharge occurring during the month of November.
The largest river within the catchment, the Rio Fajardo, is fed by several smaller
streams originating in the Luquillo Mountains and flows seaward in an easterly direction,
eventually draining into Vieques Sound in eastern Puerto Rico. At its headwaters, the Rio
Fajardo catchment drains a tropical rainforest with steep volcanic bedrock valleys, while
the downstream portion of the river (Fig. 3.1B) drains Quaternary alluvium draped across
the coastal plain. The town of Fajardo is situated along the North banks of the Rio
Fajardo near its mouth, where river flow becomes tidally influenced [Clark and Wilcock,
2000]. A small coral reef, Cayo Ahogado, is located approximately 1 km from the mouth
of the Rio Fajardo (Fig. 3.1B) and is characterized by low percent cover of scleractinian
and alcyonacean corals [Goenaga and Cintron, 1979], with members of the genera
Montastraea sp., Porites sp., and Siderastrea sp. being the most common of the
Scleractinia.
Coral sampling
On 5 October 2004, the Fajardo coral core (FJ3) was taken from a 0.63 m tall
colony of Montastraea faveolata growing on the seaward fore-reef slope of Cayo
Ahogado (N 18º 19.413’; W 065º 37.084’) at 6 m water depth, using a hand-held
submersible pneumatic drill. M. faveolata is the mounding form of the M. annularis
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species complex [Knowlton et al., 1992], and is one of most abundant and commonly
utilized Caribbean coral species for geochemical analyses [Watanabe et al., 2002; Smith
et al., 2006; Grottoli and Eakin, 2007]. The colony selected for coring was alive, had no
visible signs of partial or mass-mortality at the top of the colony where the cored was
taken, and did not appear to be undercut by bioerosion at the base of the colony. After
removing the core, the bore hole was back-filled with loose rubble taken from the
surrounding reef and sealed with an epoxy cap. The Fajardo core was 3 cm in diameter
and consisted of four segments totaling 62.5 cm in length. Each core segment was cut
longitudinally into ~6 mm thick slabs, washed with high pressure deionized water, and
dried overnight at 60º C. Core sections were x-radiographed at the Nova Southeastern
University Oceanographic Center. X-radiographs were produced by placing the core
slabs on Kodak Industrex AA440 ready-pack film and exposing them to X-rays at 70
KvP and 15 ma for 7.0 s with a source-to-object distance of 1 m. Films were manually
developed based on the specifications of the manufacturer and negatives were digitized
using a single-line medical film scanner. The resulting density band images were used to
determine the growth chronology of the Fajardo coral [Knutson et al., 1972; Buddemeier
& Kinzie, 1976].
When developing the growth chronology and age model of the Fajardo core, pairs
of high- and low-density bands were considered to be annual [Dodge and Vaisnys, 1975;
Hudson et al., 1976], with the high density portion of each annual band forming in early
summer [Watanabe et al., 2002; Kilbourne et al., 2007]. Density bands were counted by
three different persons, and the age of the core represents a consensus of the three
independent counts. Additional constraint on the age model was achieved by comparing
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Δ14C measurements made in this study with other records available from the Atlantic and
Caribbean corals [compiled by Grottoli and Eakin, 2007] and ensuring that the
chronology developed via counting density bands corresponded with the timing of the
base and peak of the bomb radiocarbon signal within the FJ3 core.
Samples of the coral skeleton for geochemical analysis were sequentially shaved
to a depth of ~1.5 mm and collected at 1 mm intervals along the major axis of maximum
growth, yielding a total of 323 samples. Sampling was performed along the path shown in
Figure 3.2 using a handheld Dremel drill fitted with 1 mm diameter diamond dental drill
bits. Coral skeletal samples were also examined at high-resolution for a section between 5
and 15 mm from the top of the core. For these samples, tthe skeleton was milled at 0.1
mm increments along the same sampling path using a Merchantek Micromill drilling
apparatus. This high-resolution sampling produced a total of 100 individual samples. All
skeletal sample material was individually homogenized into a fine powder using an agate
mortar and pestle. Since larger sample amounts were required for radiocarbon analysis,
additional skeletal material was drilled in a horizontal plane immediately adjacent to the
corresponding stable isotope sample path (Fig. 3.2). Samples for radiocarbon analysis (N
= 54) were taken where large negative δ13C excursions were measured within the coral
skeleton.
Water sampling
Sub-surface (0.5 – 1.5 m) river and seawater samples were collected for the
analysis of the δ13C and Δ14C of DIC (DI-δ13C and DI-Δ14C, respectively) during both the
wet (October 2004 & 2007) and dry seasons (March 2005 & 2008). Samples were
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collected along a transect in the lower Fajardo catchment and coastal zone at the
following locations: up-river, at the river mouth, in the nearshore waters seaward of the
river mouth, in the bay at a median distance to Cayo Ahogado, and directly above the
coral reef at Cayo Ahogado (Fig. 3.1). Each water sample was collected by peristaltic
pump, filtered through a pre-baked (500º C) Whatman QMA filter (0.7 μm pore size),
individually stored in pre-cleaned (10% HCl, baked at 500º C) glass bottles, poisoned
with mercuric chloride, and sealed with an air-tight crimp-top rubber seal. All samples
were stored in the dark and held at room temperature. Duplicate samples at the up-river
and reef locations were collected each season. In addition, geographic location (latitude
and longitude), salinity, pH, water temperature, and water transparency were recorded at
each collection site.
Stable isotope analyses
For each coral stable isotope sample, approximately 100 µg of finely ground
skeletal powder was acidified at 70°C with 100% H3PO4 in an automated Kiel III
carbonate autosampling device. δ13C and δ18O of the resulting CO2 gas were measured
with a Finnigan MAT 252 triple collecting stable isotope ratio mass spectrometer (SIRMS) in Grottoli’s laboratory. Only δ13C values are presented here and are reported as the
per mil deviation of the ratio of 13C:12C relative to the Vienna Pee Dee Belemnite
(VPDB) limestone standard [Coplen, 1996]. Ten percent of all measurements were made
in duplicate. The standard deviation of repeated measurement of an internal standard (n =
83) and duplicate samples (n = 40) was ≤ ±0.05‰.
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DIC samples were prepared for isotopic analyses using methods similar to those
described by Kroopnick [1974]. Briefly, each sample was acidified with ortho-phosphoric
acid, sparged under helium flow, and the resulting CO2 cryogenically purified under
vacuum. The resultant CO2 gas was then split into two glass ampoules: one for δ13C and
one for Δ14C analyses. DI-δ13C measurements were carried out by cracking the CO2 gas
ampoules into a multiport inlet system connected to a Finnigan Delta Plus IV SIR-MS in
Grottoli’s laboratory. Ten percent of all DI-δ13C measurements were made in duplicate.
Repeated measurement of an internal standard (n = 44) had a standard deviation of
±0.02‰. All DI-δ13C measurements are reported in per mil (‰) relative to the VPDB
standard.
Radiocarbon analyses
A sub-set of coral skeleton samples was analyzed for Δ14C. Approximately 10 mg
of homogenized coral skeletal powder were sent to the Keck Accelerator Mass
Spectrometer (AMS) facility at the University of California-Irvine for high-precision 14C
analysis. Sub-samples (8 mg each) were converted to CO2 in evacuated Vacutainers®
with 85% phosphoric acid, then further converted to graphite using an iron catalyst with
H2 gas as the reducing agent [Vogel et al., 1987]. The ratios of 14C/12C and 13C/12C were
measured using an NEC 0.5 MV compact AMS and background subtraction was applied
using 14C-free spar calcite. The standard deviation of all coral Δ14C measurements was
±1.7‰.
For all DI-∆14C analyses, ampoules of CO2 gas extracted from samples collected
in 2004 and 2005 were sent to the National Ocean Service Accelerator Mass
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Spectrometry (NOSAMS) facility at Woods Hole Oceanographic Institute (WHOI), while
samples collected in 2007 and 2008 were sent to the Arizona AMS Laboratory at the
University of Arizona for analyses. For both sets of samples, CO2 gas was converted to
graphite using an Fe catalyst and the ratio of 14C/12C was measured via AMS, with
background subtraction applied using 14C-free groundwater. The standard deviation of all
DI-∆14C measurements was ±5.0‰
All radiocarbon measurements (coral and DIC) were reported as fraction modern
and converted to Δ14C (the per mil deviation of 14C/12C in the sample relative to that of
the 95% Oxalic Acid-1 standard) according to the conventions of Stuiver and Polach
[1977] for geochemical samples with known age. Since simultaneous measurement of 13C
and 14C were possible at the Keck AMS facility, coral Δ14C results were corrected for
fractionation using the δ13C values measured by the AMS. Simultaneous measurements
of 13C and 14C were not possible for DIC analyses, therefore DIC-Δ14C results were
corrected for fractionation using δ13C values measured via SIR-MS.
Data analysis
δ13C data from the Fajardo coral core were compared to Rio Fajardo (Station
50071000) discharge data available from the United States Geological Survey [USGS,
2008]. Since these two data sets are structured as stochastic time-series, periodicity trends
within individual data sets were examined using single spectrum analysis based on a fast
Fourier transform of the co-variance function, and co-variation and correlation between
the two stochastic time series was tested for using bivariate cross-spectral analysis
[Chatfield, 2004]. A Hamming window (width = 5) was applied to both time series.
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Coherency confidence limits were estimated using the methods described by Thompson
[1979]. Prior to spectral analysis, δ13C and river discharge time series were de-trended by
subtracting the long-term linear mean from each data point. All time series analyses were
performed using Statistica version 8 (© 2007 StatSoft, Inc.).
The Pearson product-moment correlation coefficient was calculated in order to
determine the degree of interdependent covariation between detrended coral δ13C and
Δ14C [Sokal and Rohlf, 1995]. Coral δ13C and Δ14C were detrended as describe above.
The average trend of coral Δ14C was considered to be linear in three distinct sections of
the bomb-radiocarbon signal. A linear long-term mean was calculated and subtracted
from each of 1) the pre-bomb portion of the record (1948 - 1956); 2) the mid-record
appearance and rise of bomb-radiocarbon (1956 - 1972); and 3) the post-bomb portion of
the record (1972 - 2004). Interdependent covariation between DIδ-13C and -Δ14C was also
determined using Pearson product-moment correlation. Statistical difference between
correlations in coral skeleton and ambient waters was tested using a Fisher t test [Fisher,
1921]. In this test, the statistic (t) is computed as the difference between the slopes of
each correlation divided by the standard error of the difference between those slopes.
A fully factorial model III analysis of variance (ANOVA) was used to test for
differences in both DI-δ13C and DI-Δ14C between the wet and dry seasons, and riverine
and seawater end-member values. Averaged values are reported as arithmetic means ± 1
standard deviation, and differences were considered statistically significant at p ≤ 0.05.
DI-δ13C and DI-Δ14C values were determined to be normally distributed via Lilliefors test
for normality [Lilliefors, 1967] based on the Kolmogorov-Smirnov distribution prior to
ANOVA analyses. Except where indicated, all statistical analyses were conducted using
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SAS version 9.1.3 of the SAS System for Windows (© 2000-2004 SAS Institute Inc.
SAS and all other SAS Institute Inc. product or service names are registered trademarks
or trademarks of SAS Institute Inc., Cary, North Carolina, USA.).
A first-order estimate of the contribution of terrestrially-derived DIC to the
isotopic signature recorded in coral skeleton was made for both the wet and dry season
using a simple two end-member mass-balance equation:
δ13Ccoral = x δ13CFW + (1-x) δ13CSW
(Equation 3.1)
In this equation, x is the unknown proportion being solved for, δ13Ccoral represents
average detrended δ13C minima (wet season) and maxima (dry season) for the entire coral
skeletal record, δ13CFW represents the average freshwater end-member DI-δ13C values
measured in the Rio Fajardo (river and river mouth sites) during the wet or dry season,
and δ13CSW represents the average marine end-member DI-δ13C values measured in the
offshore waters adjacent to the Rio Fajardo catchment (bay and reef sites) during the wet
or dry season. An error term for this estimate was calculated use standard arithmetic rules
of error propagation. By using the detrended coral δ13C minima, any long-term trends
present in the coral δ13C were excluded from the mass-balance. Since metabolic effects
were not directly measured, they cannot be accounted for in the mass-balance equation. A
similar calculation was made for the Δ14C of coral skeleton and DIC, however due to the
radiogenic nature and presence of bomb 14C, a reliable estimate could not be obtained and
is therefore not reported.
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RESULTS
Coral growth & chronology
X-radiographs of the Fajardo coral skeleton showed that only the top two sections
of the core were oriented parallel to growth axis. Therefore, only these two core sections
(total length = 32.3 cm) were used in this study. In total, 56 distinct annual density band
couplets (1 couplet = 1 high- and 1 low-density band) were identified, indicating that
coral growth spanned the period from 1948 to 2004 (Fig. 3.2). The high density portion
of the coral skeleton is visible near the very top of the core (2004), indicating early to
mid-summer deposition of this portion of the skeleton. The annual growth rate in terms of
linear skeletal extension (LSE) ranged from 3.8 to 8.1 mm yr-1 with a mean annual LSE
rate of 5.72 ± 1.20 mm yr-1. Thus on average, each low resolution (1 mm) coral δ13C
sample represents two months of coral growth while each high resolution (0.1 mm) coral
sample represents approximately 1 week of coral growth.
Coral skeletal δ13C & Δ14C
Coral δ13C values ranged from -3.12 to 0.44‰ and had an overall average of -1.01
± 0.65‰ (Fig 3.3). Average annual δ13C decreased at a rate of 0.018‰ yr-1 over the span
of the record (Fig. 3.3). Single spectrum analysis revealed a high spectral density with
annual periodicity for the entire detrended coral δ13C record. Annual δ13C minimum
values typically occurred in the latter half of each year (range = June to January), and
occurred most frequently during late November through early December. Average annual
δ13C minima (-1.62 ± 0.58 ‰) were significantly lower than average annual maxima (0.51 ± 0.42 ‰; t-test, tstat = -13.486, df = 55, p < 0.001). Cross spectral analysis of Rio
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Fajardo discharge (independent variable) and the coral δ13C time series (dependent
variable) revealed significant annual coherence (0.822, p = 0.05; Fig. 3.4). The two
variables covaried in a near anti-phase relationship (phase angle = 178º), such that as
discharge increased coral δ13C anomalies decreased. During the wet season, the
proportion of the contribution of land-derived DI-δ13C to the detrended δ13C minima
within the coral skeleton, ignoring metabolic effects, was calculated to be 24.8 ± 4 %.
The dry season contribution of land-derived DI-δ13C to the detrended coral δ13C maxima
values was calculated to be and 16.8 ± 8 %, ignoring metabolic effects.
The coral Δ14C record exhibited a clear bomb radiocarbon signature (Fig. 3.3).
Average Δ14C decreased by 6‰ from1948 to 1956 (-0.8‰ yr-1), increased by 208‰ from
1956 to 1972 (13‰ yr-1), and then decreased by 87‰ from 1972 to 2004 (-2.7‰ yr-1).
Coral skeletal δ13C and Δ14C anomalies were positively correlated (R = 0.371; p = 0.011;
Fig. 3.6), and synchronous depletions of both δ13C and Δ14C anomalies were present for
the periods 1950 to 1960 and again from 1975 to 2004. No clear relationship was shown
between the coral skeletal δ13C and Δ14C anomalies for the period 1960 to 1975, which is
the timing of the maximum increase in bomb radiocarbon within the Fajardo coral (Fig.
3.5).
DIC δ13C & Δ14C
DI-δ13C values ranged from -9.82 to 0.93‰ (Table 3.1). Average freshwater
(Upriver and River Mouth) values were significantly more depleted than average
seawater (Bay and Reef) values (Table 3.2). In addition, average wet season DI-δ13C was
more depleted than average dry season DI-δ13C, however this difference was not
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statistically significant (Table 3.2). DI-Δ14C values were all modern (post-bomb), and
ranged from 20.6 to 78.3‰ (Table 3.1). Average freshwater DI-Δ14C was significantly
more depleted than average seawater values (Table 3.2). In addition, average wet season
DI-Δ14C was significantly more enriched than corresponding average dry season DI-Δ14C
(Table 3.2). DI-δ13C and DI-Δ14C were positively correlated (R = 0.842; p < 0.001; Fig.
3.7). The slope of this correlation was not significantly different from the slope of the
correlation between coral skeletal δ13C and Δ14C anomalies (Fisher’s t-test; tstat = 0.82, df
= 60, p ≤ 0.05).
DISCUSSION
Coral growth
The average LSE rate measured in the Fajardo core (5.2 mm yr-1) is much lower
than those reported for the Montastraea complex elsewhere in the Caribbean region.
Shallow water (1-10 m) Montastraea complex corals have annual growth rates in the
range of 7 - 10 mm yr-1, with LSE rates of M. faveolata typically being on the high end of
that range [Gladfelter et al., 1978; Hubbard and Scaturo, 1985; Risk et al., 1992;
Carricart-Ganivet et al., 2000; Moses and Swart, 2006]. The observed LSE was more
similar to that of M. annularis complex corals reported from depths of 14 m at Tobago
[Moses and Swart, 2006], 18-37 m at St. Croix [Hubbard and Scaturo, 1985], and 44 m
at Barbados [Runnalls and Coleman, 2003]. Since Cayo Ahogado is located a shallow
embayment ~1 km from the mouth of the Rio Fajardo, sedimentation and turbidity are
likely major factor in limiting coral growth rates on the reef. The deleterious effects of
turbid waters on coral growth are well documented and can be caused by the delivery of
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suspended sediments via rivers to coastal reefs, and by the resuspension of those
sediments off of the seafloor [Dodge et al., 1974]. Several studies have also attributed
slow growth rates of the Montastraea complex to terrigenous sedimentation at other
locations within insular Puerto Rico [Loya, 1976; Morelock et al., 1983; Torres and
Morelock, 2002]. Sediment yields from small mountainous rivers, such as the Rio
Fajardo, are known to be large [Milliman and Syvitsky, 1996] and are therefore capable of
producing turbid conditions that would slow or limit coral growth. Secchi depth
measurements made at the times of water collections never exceeded 4.0 m, and the
seafloor (max. depth = 7 m) was never visible even during the dry season. Therefore, the
reduced growth rates observed in the Fajardo core are likely due to the coral growing in
turbid waters, and suggest a physical link between river discharge and corals growing at
Cayo Ahogado.
Coral skeletal δ13C & Δ14C
The observed decrease in mean δ13C over the span of the coral record (-0.018‰
yr-1; Fig. 3.3) is consistent with the observed rate of decrease in tropical atmospheric δ13C
(-0.02‰ yr-1) [Keeling et al., 2005]. This phenomenon, termed the “13C Suess effect”, is a
result of the increased anthropogenic input of 13C-depleted fossil fuel CO2 into the
atmosphere. The similarity in depletion rates between the 56-year coral skeletal δ13C
record and atmospheric δ13C strongly suggest that the 13C Suess effect is driving the longterm average δ13C decrease observed in the Fajardo core. Long-term trends in coral
skeletal Δ14C (Fig. 3.3) were clearly driven by the influx of bomb radiocarbon. Both the
amount (156.63‰) and occurrence of peak bomb radiocarbon values measured in the
120
1972 growth band of the Fajardo coral are consistent with published values (~160‰ and
1970-1975, respectively) from other coral records in the western Atlantic/eastern Pacific
region of the Northern Hemisphere [compiled by Grottoli and Eakin, 2007].
Additionally, the rate of increase of bomb radiocarbon within the Fajardo coral (13.01‰
yr-1) falls squarely within the range (5.81 – 18.99‰ yr-1) of those reported by Grottoli
and Eakin [2007] for corals growing in the western Atlantic/eastern Pacific region of the
Northern Hemisphere.
Coral skeletal δ13C anomalies (i.e., Suess effect trend removed) were shown to
exhibit annual periodicity over the span of the coral record (Figs. 3.3 and 3.4). Annual
periodicity of δ13C has been reported for M. faveolata in the Caribbean and western
Atlantic region [Fairbanks and Dodge, 1979; Halley et al., 1994; Swart et al., 1996],
although the timing of annual maxima and minima varies among geographic locations
and individual records. This has given rise to a range of different interpretations as to the
source of annual δ13C variation in coral skeletal records [see reviews by Swart, 1983;
Swart et al., 1996; Grottoli, 2001]. The timing of the annual maxima (early summer) and
minima (very late autumn) reported here do not coincide with those reported in Florida
(max. = mid-spring, min. = mid-summer) [Swart et al., 1996], and occur just prior to
those reported in Barbados and Jamaica (max. = mid-summer, min. = early winter)
[Fairbanks and Dodge, 1979].
In the Fajardo core, skeletal δ13C anomalies were coherent with river discharge
(Fig. 3.4) such that δ13C minima occurred during times of increased Rio Fajardo
discharge. First-order mass-balance calculations show that as much as 25% of the δ13C
signature of the Fajardo coral skeleton may be influenced by riverine DIC inputs during
121
the wet season. Conversely in the dry season, only 17% of the δ13C signature may be
derived from riverine DIC. Thus, the seasonal periodicity of riverine DIC input to the
coastal ocean is likely influencing the annual periodicity observed in coral skeletal δ13C,
with lower coral δ13C corresponding to the timing of the wet season. However, coral
skeletal δ13C can not be used alone to distinguish whether the observed depletions are a
result of increased riverine DIC input to coastal ocean, or the result of metabolic changes
brought about by associated wet season phenomena (e.g. increased cloud cover or
turbidity).
Although a decrease in light driven by increased in cloud cover or turbidity during
the wet season can also drive skeletal δ13C towards more negative values [e.g. Grottoli
and Wellington, 1999], decreased light would not produce a change in the Δ14C of the
coral skeleton. In the Fajardo core, skeletal δ13C and Δ14C exhibit synchronous depletions
coincident with increases in river discharge (Fig. 3.5), suggesting a non-metabolic
influence on the δ13C and Δ14C of the coral skeleton brought about by changes in
surrounding DIC and corals during these events. These synchronous depletions primarily
occur within the low-density portion of the annual growth bands, immediately following
the deposition of the high-density portion of the annual band. According to the age model
constructed for the Fajardo core, the timing of these synchronous δ13C and Δ14C
depletions occur between the months of October and January, which is coincident with
the timing of the wet season in the Rio Fajardo catchment. The inverse relationship
between coral skeletal δ13C and river discharge coupled with the synchronous wet-season
depletion of both δ13C and Δ14C in the coral skeleton are evidence that an influx of
122
riverine DIC is influencing the carbon isotopic signature of the Fajardo coral during the
wet season when river discharge is the greatest.
Relationship between DIC and coral skeletal isotopes
The influence of terrestrially derived DIC on the geochemistry of the Fajardo
coral skeleton becomes more apparent when examined in the context of the DI-δ13C and Δ14C presented in this study. The correlations between δ13C and Δ14C anomalies in the
coral skeleton (Fig. 3.6) and ambient DI-δ13C and DI-Δ14C (Fig. 3.7) were not
significantly different, and both δ13C and Δ14C were more depleted in riverine versus
coastal seawater DIC. This suggests that when large pulses of river water bathe the reef,
the DI-δ13C and DI-Δ14C of those waters should decrease relative to open ocean seawater
values. Since peak Rio Fajardo discharge occurs in October and November, the isotopic
influence of riverine DIC in coastal seawater DIC should be most pronounced during
those months. Other studies within Puerto Rico have also shown similar patterns in the
annual variability of coastal seawater DI-δ13C. Watanabe et al. [2002] reported monthly
DI-δ13C measurements from a reef at La Parguera, in southwestern Puerto Rico, over a
1.5 year period. Their results also show DI-δ13C to be more depleted during the months of
October and November, and more enriched from January through August. In their
interpretation, the influence of δ13C-depleted freshwater plumes emanating from the
Orinoco River is cited as a source of the observed seasonality of DI-δ13C over local
sources of depleted DI-δ13C. However, the data presented in this study suggest local
sources of terrestrial DIC are highly capable of influencing the isotopic composition of
coastal waters.
123
Since the Fajardo catchment is subject to seasonal climatic variability, it follows
that most δ13C and Δ14C depleted freshwater would mix with coastal waters during the
wet season (May to mid-January). Moyer et al. [Chapter 2, this dissertation] have shown
that DI-δ13C and DI-Δ14C both mix conservatively from the Rio Fajardo to the reef at
Cayo Ahogado during the wet season, but not during the dry season in Fajardo. This
seasonal difference suggests that the DI-δ13C and -Δ14C waters bathing the reef at Cayo
Ahogado are only influenced by riverine input to the coastal ocean during the wet season.
Accordingly, the δ13C and Δ14C signature of the coral skeleton is expected to record the
influence of riverine DIC most faithfully at times when river discharge is large enough to
cause conservative isotopic mixing between fresh and seawater DIC (i.e. during the wet
season).
Relationship between river discharge and coral skeletal isotopes at high sampling
resolution
Comparison of coral skeletal δ13C anomalies analyzed at both high- and low
resolution (0.1 mm and 1.0 mm, respectively) over an approximately 2 year period of
Fajardo coral growth reveals the same pattern of seasonal δ13C variability for both
records (Fig. 3.8). However, the high-resolution record exhibited a higher amplitude and
greater intra-annual variability. These findings are consistent with other studies that have
examined sampling resolution as a consideration of coral isotope interpretation in the
Montastraea sp. complex [Halley et al., 1994; Leder et al., 1996, Smith et al., 2006].
Given the links between freshwater DIC delivery and coral carbon isotopes, it was
expected that high-resolution δ13C measurements could help identify individual river
124
discharge events (i.e. floods). However, when the high-resolution δ13C anomalies are
examined in relation to weekly Rio Fajardo discharge there is no clear relationship
between peaks in river discharge and decreases in coral skeletal δ13C (Fig. 3.8).
Meanwhile at longer time intervals (monthly – seasonal) the general relationship between
increased river discharge and decreased coral skeletal δ13C anomalies does hold (Fig.
3.8). These data indicate that either the geochemistry of coral skeletons is not sensitive to
single river discharge events, or samples analyzed at approximately weekly intervals do
not have sufficient resolution to identify individual river discharge events. Furthermore,
these data also demonstrate the importance of using paired measurements of δ13C and
Δ14C to detect riverine influence in coral skeletons. Without the simultaneous analysis of
Δ14C, which is not possible at high resolution due to the large quantity of coral powder
required for AMS analyses, it is impossible to know whether the variability observed in
the high resolution coral δ13C record is due to metabolic effects or changes in river
discharge.
Conceptual model
The data presented here strongly suggest that land-derived DIC is indeed
influencing the skeletal carbon isotope signature of the Fajardo coral core during the wet
season. To reconcile these data, a conceptual model (Fig. 3.9) is presented showing the
sources of carbon to the Rio Fajardo and coastal ocean, the δ13C and Δ14C signature
associated with the dominant carbon pools, how these relationships change with seasonal
changes in river discharge, and how that ultimately influences the δ13C and Δ14C in the
skeletal record. The DIC isotopic values presented in the model are based on direct
125
measurements made in this study (Table 3.1), dissolved and particulate organic carbon
(DOC and POC, respectively) δ13C and Δ14C values are based on published
measurements within the study area [Moyer et al., Chapter 2, this dissertation], and soil
and plant organic matter isotope values in Puerto Rico were drawn from the published
literature [von Fischer and Tieszen, 1995].
A major source of DIC in riverine systems is the conversion of dissolved and
particulate organic carbon (DOC and POC, respectively) into DIC via both abiotic (e.g.
photo-oxidation) and biotic (e.g. respiration) processes [Raymond and Bauer, 2001a,b;
Mopper and Kieber, 2002]. Plant biomass and surface soils are the main sources of
organic carbon to rivers, and have δ13C values reflective of the vegetation within the river
catchment. In a primarily forested (C3 plants) catchment such as Fajardo, plant organic
matter has an average δ13C of -30‰, and soil organic matter ranges from -26 to -28‰
[von Fischer and Tieszen, 1995]. Prior to mobilization and transport by rivers, soil
organic matter may age significantly on land [Blair et al., 2003; Cole and Caraco, 2001;
Kao and Liu, 1996; Masiello and Druffel, 2001; Raymond and Bauer, 2001a], and the
majority of this aged organic matter is broken down and transported in the form of DOC
[Aitkenhead-Peterson et al., 2003, 2005; Hope et al., 1994]. The fraction of aged soil
organic matter that is not converted to DOC is transported to the coastal ocean via rivers
as POC.
A significant portion of both the DOC and POC pools are highly bioavailable in
river systems and are ultimately converted to DIC before reaching the river mouth
[Raymond and Bauer, 2001a; Mopper and Kieber, 2002]. Estuarine processes also play
an important role in the degradation and conversion of riverine DOC and POC into DIC,
126
and a significant portion of terrestrial organic carbon is altered in estuarine waters
[Robertson and Alonghi, 1995; Raymond et al., 2003; Wang et al., 2004]. Since the
organic carbon is aged and δ13C-depleted, this conversion produces DIC that is also
relatively aged and δ13C-depleted compared to seawater values. Riverine DI-δ13C and DIΔ14C values measured in this study were always more depleted than seawater DIC values
(Table 3.1). The lighter riverine DI-δ13C isotopes reflect a δ13C-depleted organic carbon
source, however the lack of pre-bomb DI-Δ14C in any of the samples suggests that the
DIC being transported to the reef is reflective of a source that represents a mixture of
modern and old organic matter (Fig. 3.9). Regardless of the source of the isotopic
signature of the DIC, both the δ13C and Δ14C of the river waters being transported to the
coastal region are more depleted than those of the ocean surface waters. The conversion
of DOC and POC into DIC is thus reflected in the conceptual model (Fig. 3.9). However,
the istopic signature of DIC becomes the focus of the model from the river mouth to the
reef (Fig. 3.9) since DIC is thought to be the abiotic source of seasonal isotopic
variability within the coral skeleton.
The seasonal component of riverine DIC influence to the coastal ocean, and
ultimately the coral skeleton, is also reflected in the conceptual model (Fig 3.9A, B).
During the wet season (Fig. 3.9A), the riverine DIC isotopes are shown to mix
conservatively [Moyer et al., Chapter 2, this dissertation] along a salinity gradient caused
by the river discharge plume. This same pattern does not hold true during the dry season
(Fig. 3.9B) when river discharge is generally diminished and riverine DIC does not, at
least isotopically, mix conservatively across the salinity gradient [Moyer et al., Chapter 2,
this dissertation]. It therefore follows that coral δ13C and Δ14C are only shown to be
127
affected by the isotopic signature of terrestrially-derived DIC during the wet season, with
the observed response being relative depletions in both δ13C and Δ14C within the coral
skeleton.
Implications for proxy records
Given the influence of terrestrially-derived DIC on coral skeletal δ13C and Δ14C
values in the Fajardo core, the findings presented here have several implications for
interpreting proxy records for palaeo-reconstructions. When skeletal δ13C and Δ14C are
measured in tandem at sub-annual resolution, it is possible to resolve the seasonal
influence of terrestrially derived DIC on coral skeletal geochemistry. This dual isotope
approach allows for a much clearer distinction between coral δ13C variability brought
about by changes in the isotopic composition of DIC and those due to metabolic effects.
However, additional controlled experimental studies are necessary in order to make this
dual carbon isotope method a fully quantitative proxy for the influence of terrestrial DIC
to the carbon isotopic signature of the coral skeleton. The use of multi-proxy records
including δ13C and Δ14C in combination with other known tracers of riverine input such
as Ba/Ca or other trace elements [Alibert et al., 2003] could help provide historical
records of riverine carbon input to reefs, in terms of both DIC and POC. With additional
experimental calibration, such records could be used as proxies for the history of landocean carbon flux for many areas of the tropics where river discharge data are few, and
local carbon cycling is not well understood. Such a proxy would be extremely useful in
helping to gain a clearer understanding of historical dynamics in tropical land-ocean
carbon flux in the context of modern global climate change.
128
Summary
In this study, paired measurements of δ13C and Δ14C were made in the DIC of a
small tropical river and the coastal ocean (Table 3.1), as well as in a coral skeleton (Fig.
3.3) from eastern Puerto Rico. These data were used to show the influence of DIC on the
δ13C and Δ14C within the coral skeleton. Three major findings were observed: 1)
Synchronous depletions of both δ13C and Δ14C in the coral skeleton (Fig. 3.5) are
annually coherent with the timing of peak river discharge (Fig. 3.4), 2) Riverine DIC was
always more depleted in δ13C and Δ14C than seawater DIC (Tables 3.1 and 3.2), and 3)
and the correlation of δ13C and Δ14C was the same in both coral skeleton (Fig. 3.6) and
the DIC of the river and coastal waters (Fig. 3.7). The observed synchronous depletions
in coral skeletal δ13C and Δ14C anomalies support the hypothesis that riverine DIC, which
was depleted in both δ13C and Δ14C relative to the open ocean, is influencing the carbon
isotopic geochemistry of the coral skeleton. Furthermore, these synchronous depletions of
coral skeletal δ13C and Δ14C were coincident with the wet season timing of peak river
discharge. These data support the hypothesis that the influence of terrestrial DIC is most
pronounced during the tropical wet season, when river discharge is largest (Fig. 3.9).
These findings suggest that coral skeletal records could be δ13C and Δ14C developed as
proxies for the history of land-ocean carbon flux for many areas of the tropics where
modern local carbon cycling is not well understood, and historical records are scarce.
Acknowledgements: This work was supported primarily by grants to AG Grottoli from
the Andrew Mellon Foundation and the National Science Foundation Chemical
129
Oceanography Program (Grant #0610487). RP Moyer was partially supported by and
OSU Presidential Fellowship and received additional funding from the American
Association of Petroleum Geologists, the American Geophysical Union, the Geological
Society of America, and the Friends of Orton Hall. We are grateful for field assistance
provided by H Anguerre, M Canals, M Cathey, C Malachowski, C Pacheco and B
Williams. RE Dodge and K Helmle facilitated the x-radiography of the coral skeletons.
Laboratory analyses were assisted by M Cathey, Y Matsui, C Paver, L Swierk, and H
Wu. We would like to thank B Williams and A Shinohara for helpful discussions during
the preparation of this manuscript, and A Carey, M Saltzman, and/or anonymous persons
for their careful reviews and suggestions which improved the overall quality of the
manuscript.
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136
TABLES
Location
Upriver
Date
Salinity
DI-δ13C
DI-Δ14C
(‰)
(‰)
Oct. 2004
0.0
-8.76
59.4
Oct. 2007
0.0
-9.82
49.8
March 2005
0.0
-8.23
26.9
March 2008
0.1
-9.02
27.4
River Mouth Oct. 2004
8.0
-3.34
59.2
Oct. 2007
2.0
-8.24
46.2
March 2005
17.0
-6.34
20.6
March 2008
11.1
-6.20
40.3
Oct. 2007
17.0
0.03
67.8
March 2008
35.8
0.62
62.9
Oct. 2004
36.0
0.66
71.2
Oct. 2007
26.0
0.87
70.9
March 2005
36.0
0.89
65.1
March 2008
36.1
0.91
71.6
Oct. 2004
34.5
0.71
78.3
Oct. 2007
36.0
0.92
73.9
March 2005
38.0
0.93
70.7
March 2008
35.5
0.86
68.1
Nearshore
Bay
Reef
Table 3.1. Stable (δ13C) and radiocarbon (Δ14C) isotope values measured in the dissolved
inorganic carbon (DIC) of river and seawater at the Rio Fajardo catchment in eastern
Puerto Rico. Sampling date and salinity at the time of sampling are also given.
137
DI-δ13C
Source
Model
Salinity
Season
Salinity*Season
df SS
F
p
3 301.49 153.54 < 0.001
1 301.45 460.56 < 0.001
1
2.38 3.64 0.0828
1
1.74 2.70 0.1287
DI-Δ14C
Source
df SS
F
Model
3 4879.23 48.78
Salinity
1 3600.00 107.98
Season
1 873.20 26.19
Salinity*Season 1 406.02 12.18
p
< 0.001
< 0.001
< 0.001
< 0.005
Table 3.2. Results of a fully factorial model III analysis of variance (ANOVA) for both
DI-δ13C and DI-Δ14C data. df = degrees of freedom. SS = sum of squares. F = calculated
F statistic. p = probability. Sources of variability are significant when p ≤ 0.05.
138
FIGURES
Figure 3.1. Geographic setting of the study. A) Landsat 7 image of Puerto Rico, showing
the location of the Fajardo study area within Puerto Rico (image publicly available at
www.nasa.gov). B) USGS 1:24000 aerial image mosaic of the lower Fajardo River
Catchment. Orange circles indicate water sampling locations and the black circle with
orange ring indicates where the Fajardo coral core was collected as well as the water
sampling location over the reef at Cayo Ahogado (images publicly available at
www.usgs.gov).
139
Figure 3.2. X-radiograph positive prints of the top two sections of the Fajardo coral core.
The age model based on annual bands is displayed along the right side of each core
section. The drill paths for stable and radiocarbon isotopic analyses are shown by the red
and blue lines, respectively.
140
1
150
0
-1
50
-2
Δ14C (‰)
δ13C (‰)
100
0
-3
13
δ C
14
Δ C
Long-term δ13C trend (Suess effect)
-4
-50
-100
1950
1960
1970
1980
1990
2000
Year
Figure 3.3. Stable- (δ13C) and radiocarbon (Δ14C) values measured for the Fajardo coral
core (1948 – 2004). δ13C = open circles connected by solid grey line. Δ14C = red
triangles. Average δ13C trend = dashed black line.
141
600
A
Co-spectral density
Cross quadrature density
Cross-periodogram (Real)
Spectral Density
400
200
0
1.0
B
95% Confidence level
99% Confidence level
Squared Coherency
0.8
0.6
0.4
0.2
0.0
10
1
Period (Years)
0.1
Figure 3.4. Results of cross-spectral analysis between Rio Fajardo discharge and the
Fajardo coral skeletal δ13C time series. A) Spectral density estimates of the crossspectrum (co-spectral and cross quadrature densities) and the smoothed crossperiodogram. B) Squared coherency of the two time series.
142
10
Coral Skeleton
14
Δ C anomalies (‰)
5
0
-5
-10
DI-Δ14C anom. = 2.75(DI-δ13C anom.) + 1.137
Correlation: r = 0.444; p < 0.004
-15
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
13
δ C anomalies (‰)
Figure 3.5. Fajardo coral skeletal δ13C vs. Δ14C anomalies. The linear correlation = solid
grey line; 95% confidence intervals = grey dashed lines.
143
15
10
5
0
0
-5
14
Δ C anomalies (‰)
13
δ C anomalies (‰)
1
-1
-10
13
δ C anomalies
14
Δ C anomalies
-2
-15
1960
1970
1980
1990
2000
Year
Figure 3.6. Stable- (δ13C) and radiocarbon (Δ14C) anomalies in the Fajardo coral core for
the period 1955 - 2004. δ13C anomalies = open circles connected by solid grey line. Δ14C
anomalies = red triangles connected by red lines.
144
100
River and Seawater DIC
DI-Δ14C (‰)
80
60
40
20
DI-Δ14C = 3.405(DI-δ13C) + 66.734
Correlation: r = 0.842; p < 0.001
0
-12
-10
-8
-6
-4
-2
0
2
13
DI-δ C (‰)
Figure 3.7. Fajardo river and coastal seawater DI-δ13C vs. DI-Δ14C. Linear correlation =
solid grey line; 95% confidence intervals = grey dashed lines.
145
δ13C (‰)
50
1
40
0
30
-1
20
-2
10
-3
Discharge (m3 s-1)
2
0
2002.5
2003.0
2003.5
2004.0
Year
Figure 3.8. High resolution (0.1 mm) stable carbon isotope (δ13C) anomalies in the
Fajardo coral core for the period 2002 - 2004. High resolution δ13C anomalies = open
circles connected by black line. Low resolution (1.0 mm) δ13C anomalies = grey circles.
Smoothed (weekly) Rio Fajardo discharge (blue line) is also shown.
146
Figure 3.9. Conceptual model showing the flow of major sources of carbon from within
the Rio Fajardo catchment to the coastal ocean. The δ13C and relative 14C ages are given
for each of the dominant carbon pools. The dominant season variability of δ13C and Δ14C
signatures in the coastal ocean, and influences on the δ13C and Δ14C in the skeletal record
are shown for the wet (A) and dry (B) seasons. δ13C and Δ14C reflect published values for
dissolved inorganic carbon (DIC; this study), dissolved and particulate organic carbon
(DOC and POC, respectively) [Moyer et al., Chapter 2, this dissertation], and soil and
plant organic matter within Puerto Rico [von Fischer and Tieszen, 1995; Marin-Spiotta et
al., 2008]. 14C relative ages range from modern (‘mod’) to ‘old’, with intermediate values
designated as ‘aged’.
147
CHAPTER 4
A MULTI-PROXY RECORD OF TERRESTRIAL INPUTS TO THE COASTAL
OCEAN USING TRACE ELEMENTS (Ba/Ca, Mn/Ca, Y/Ca) AND CARBON
ISOTOPES (δ13C, Δ14C) IN A CORAL SKELETAL CORE
Ryan P. Moyer, Andréa G. Grottoli, and John Olesik
The Ohio State University, School of Earth Sciences,
125 South Oval Mall, Columbus, OH 43201 USA
Chapter 4 is formatted as a manuscript intended for submission to the journal
Paleoceanography, published by the American Geophysical Union.
Keywords: Coral geochemistry; Carbon isotopes, Trace elements, Puerto Rico, Landocean carbon flux.
148
ABSTRACT
Rivers are principle sources of terrestrial sediments, trace elements, and organic material
to coastal waters. Small mountainous rivers (SMRs) are thought to be major contributors
of terrestrial material to the world’s oceans and tropical SMRs may contribute as much as
one third of the total carbon exported to the coastal ocean. The ability to quantify riverine
inputs and understand how they have changed through time is critical to understanding
local and global carbon budgets in the context of modern climate change. Corals have the
potential to provide such records in the tropics because they are long-lived and isotopic
and trace element signatures within their skeletons are useful proxies of
palaeoceanographic conditions. Here, a 56-year record of coral skeletal Ba/Ca, Mn/Ca,
Y/Ca, δ13C, and Δ14C measurements are presented from a Montastraea faveolata colony
growing ~1 km from the mouth of the Rio Fajardo in eastern Puerto Rico. Three major
findings were observed: 1) Coral Ba/Ca was highly coherent with annual river discharge
and coral skeletal δ13C, 2) Mn/Ca and Y/Ca were not annually coherent with river
discharge, and 3) increases in coral Ba/Ca were synchronous with the timing of
depletions of both δ13C and Δ14C in the coral skeleton and increases in river discharge
The strong coherence between river discharge and Ba/Ca, and the concurrent timing of
increases in Ba/Ca with decreases in δ13C and Δ14C suggest that river discharge is
simultaneously recorded by multiple geochemical records, some of which can also be
used as proxies of terrestrial carbon flux to the coastal ocean. The development of better
proxies for the history of land-ocean carbon flux would be invaluable to understanding
the role of tropical carbon fluxes in the context of global climate change.
149
INTRODUCTION
Rivers are principle sources of terrestrial sediments, trace elements, and organic
material to coastal waters. Small mountainous rivers (SMRs) are thought to be major
sources of terrestrial material to the world’s oceans [e.g. Milliman and Syvitski, 1992],
and tropical SMRs may contribute as much as one third of the carbon exported to the
global coastal oceans [e.g. Lyons et al., 2002]. The ability to quantify terrigenous inputs
to the coastal ocean and understand how they have changed through time is critical to
understanding local and global carbon budgets in the context of modern anthropogenic
land-use and climate changes. However, no such data are available for the majority of
SMRs in the topical Atlantic or Indo-Pacific regions, thus representing a major gap in our
understanding of the global carbon cycle. Trace element [Alibert et al., 2003, McCulloch
et al., 2003; Sinclair and McCulloch, 2004; Fleitmann et al., 2006; Lewis et al., 2007]
and isotope records [Moyer and Grottoli, Chap. 3, this dissertation] in coral skeletons
have been shown to be effective recorders of riverine input to the coastal ocean and may
therefore provide a history of terrestrial carbon input to the coastal ocean.
Corals are long-lived (300+ years), occur in nearly all shallow tropical waters, and
isotopic and trace elemental variations within their skeletons serve as useful proxy
records of palaeoceanographic variability [See reviews by Shen and Sanford, 1990;
Druffel, 1997; Gagan et al., 2000; Grottoli, 2001; Eakin and Grottoli, 2006; Grottoli and
Eakin, 2007]. Paired stable- (δ13C) and radiocarbon (Δ14C) isotope measurements in coral
skeleton have been shown to reflect the input of riverine dissolved inorganic carbon
(DIC) to the coastal ocean [Moyer and Grottoli, Chap. 3, this dissertation]. Additionally,
trace element concentrations in corals growing in near-shore environments have been
150
shown to record natural and anthropogenically induced changes in the delivery of
terrigenous sediments to the coastal ocean [McCulloch et al, 2003; Sinclair and
McCulloch, 2004; Fleitmann et al, 2006; Lewis et al., 2007]. The development of laser
ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) measurement
techniques specific to coral skeletons [see Sinclair et al., 1998; Fallon et al., 1999;
Matthews, 2007] has created the ability to produce high-resolution trace element records
over long periods of time.
Of the numerous trace elements that have previously been measured in corals,
Barium (Ba), Manganese (Mn), and Yttrium (Y) have been shown to have the closest
association with river discharge and terrestrial inputs [e.g. Shen and Sanford, 1990, Swart
et al., 1999, Alibert et al., 2003; McCulloch et al., 2003; Sinclair and McCulloch, 2004;
Wyndham et al., 2004; Fleitmann et al., 2006; Lewis et al., 2007]. Ba becomes a tracer of
terrigenous sediment in the ocean after desorbing from fine-grained sediments in lowsalinity estuarine environments, and then mixing conservatively along the freshwaterseawater salinity gradient [Edmond et al., 1978; Li and Chan, 1979]. Once in the marine
environment, Ba can substitute for Ca in the coral skeleton in proportion to its
concentration in sea water [Lea et al., 1989]. Additional studies have suggested that Ba
can also be incorporated into the coral skeletal matrix along with fine sediment particles,
which are also commonly rich in Ba [Sinclair and McCulloch, 2004]. Similar to Ba, Mn
and Y also exhibit desorption from suspended particulate matter in low-salinity waters
and can become incorporated in coral skeletons. At annual resolution, Mn/Ca and Y/Ca
in corals are effective tracers of anthropogenic activities on land [e.g. Fallon et al., 2002;
151
Lewis et al., 2007]. However, at sub-annual resolution both Mn and Y appear to be less
sensitive to riverine inputs than Ba.
Since paired δ13C and Δ14C measurements and trace elements in corals all record
terrestrial geochemical influence in the coastal ocean, a multi-proxy approach using
carbon isotopes and trace elements may also reveal important information about
terrestrial influence in the coastal ocean. Specifically, coral skeletal δ13C and Δ14C
combined with trace element measurements may provide a record of riverine carbon flux
to the coastal ocean. The goal of this study was to examine the relationship of δ13C and
Δ14C to Ba/Ca, Mn/Ca, and Y/Ca measured in a coral growing near the mouth of a
tropical SMR. Using this multi-proxy approach, the following hypotheses were
addressed: 1) Ba/Ca, Mn/Ca, and Y/Ca trace element ratios in a coral skeleton collected
near the river mouth are coherent on annual time scales with river discharge, 2) coral
Ba/Ca, Mn/Ca, and Y/Ca are inversely coherent with coral δ13C on annual time scales,
and 3) since terrestrially derived DIC can cause synchronous depletions of δ13C and Δ14C
in the coral skeleton, the timing of such depletions should co-occur with increases in
coral trace element ratios. If such geochemical relationships exist in the coral record, the
combined use of carbon isotopes and trace elements sensitive to river discharge may
enable the development of proxies for the delivery of terrestrial carbon to the coastal
ocean. Such information would be invaluable in the tropics where most small rivers are
not gauged or regularly monitored and local carbon cycling is not well understood. These
data are critical to understanding both local and global carbon cycles in the face of future
land-use and climate changes.
152
MATERIALS & METHODS
Geographical setting
The Fajardo river catchment is located in northeastern Puerto Rico (Fig. 4.1) and
encompasses a total area of ~ 70 km2. [Calvesbert, 1970]. Rainfall within the catchment
averages 1592 mm yr-1. There is a relatively wet season extending from May to midJanuary, with peak precipitation occurring in the months of May, October, November and
peak river discharge occurring during the months of October and November. A relatively
drier season occurs from mid-January through April.
The main river within the catchment, the Rio Fajardo, is fed by several smaller
streams originating in the Luquillo Mountains and flows seaward in a general east-west
direction. At its headwaters, the Rio Fajardo drains a tropical rainforest with steep
volcanic bedrock valleys, while the downstream portion of the river (Fig. 4.1B) drains
recent alluvium to the head of the coastal plain. The town of Fajardo is situated along the
north banks of the Rio Fajardo near the river mouth where flow becomes tidally
influenced (tidal range < 1 m) [Clark and Wilcock, 2000]. The Rio Fajardo discharges
into Vieques Sound, a large, shallow, semi-enclosed basin in eastern Puerto Rico. A
small coral reef, Cayo Ahogado, is located approximately 1 km from the mouth of the
Rio Fajardo (Fig. 4.1B). This reef is characterized by low percent cover of scleractinian
and alcyonacean corals [Goenaga and Cintron, 1979], with members of the genera
Montastraea sp., Porites sp., and Siderastrea sp. being the most common scleractinian
coral species.
153
Coral sampling
On 5 October 2004, a core (Core ID: FJ3, referred to as the Fajardo coral
throughout) was taken from a Montastraea faveolata coral colony growing on the
seaward fore-reef slope of Cayo Ahogado (N 18º 19.413’; W 065º 37.084’) at 4 m depth
using a hand-held submersible pneumatic drill. The colony selected for coring was alive
and had no visible signs of partial or mass-mortality at the top of the colony where the
core was taken, and did not appear to be undercut by bioerosion at the base of the colony.
A total of four core segments with a total length of 62.5 cm were extracted from the coral
along the maximum axis of upward growth. Each core segment was longitudinally
slabbed, cleaned, and x-radiographed in order to determine the growth chronology of the
coral colony by examining the annual density bands within the coral skeleton [Knutson et
al., 1972; Buddemeier and Kinzie, 1976]. X-radiographs of the top two sections of the
Fajardo core revealed the presence of 56 distinct annual density bands spanning the
period from 1948 to 2004 (Fig. 4.2). Annual linear skeletal extension (LSE) ranged from
3.8 to 8.1 mm yr-1 with a mean annual LSE rate of 5.72 ± 1.20 mm yr-1. Detailed methods
for preparation, x-radiography, and establishment of the growth chronology of the
Fajardo core are given by Moyer and Grottoli [Chap. 3, this dissertation]
Isotopic analyses
Detailed methods on the isotopic analysis of the Fajardo core are given by Moyer
and Grottoli [Chap. 3, this dissertation]. Briefly, coral skeleton for stable isotope analysis
was shaved at 1 mm intervals (n = 232) along a path parallel to the axis of growth in the
154
top two section of the Fajardo core (Fig. 4.2). Additional skeletal material for radiocarbon
analysis (n = 54) was drilled in a horizontal plane immediately adjacent to the stable
isotope path at uneven intervals (Fig. 4.2). Coral δ13C was measured with a Finnigan
MAT 252 triple collecting stable isotope ratio mass spectrometer (SIR-MS) in Grottoli’s
lab. The standard deviation of repeated measurement of NBS 19 (n = 83) and duplicate
samples (n = 40) was ≤ ±0.05 ‰ for δ13C. All coral δ13C measurements are reported in
per mil (‰) relative to the Vienna Pee Dee Belemnite (VPDB) standard using the
conventions of Coplen [1996]. High-precision coral skeletal radiocarbon measurements
were made using an NEC 0.5 MV compact accelerator mass spectrometer (AMS) at the
Keck AMS facility at the University of California-Irvine. The standard deviation of all
Δ14C measurements was ±1.7 ‰. Radiocarbon measurements were reported as fraction
modern and converted to Δ14C (the per mil deviation of 14C/12C in the sample relative to
that of the 95% Oxalic Acid-1 standard) according to the conventions of Stuiver and
Polach [1977].
Coral trace element measurement via laser ablation inductively coupled plasma mass
spectrometry
After removal of material for stable isotope analysis, the Fajardo coral slabs were
sectioned into seven 25 x 45 mm pieces for analysis via laser ablation inductively
coupled plasma mass spectrometry (LA-ICP-MS) in the Trace Element Research
Laboratory at the Ohio State University. Prior to analysis, each section was individually
cleaned for 30 minutes in a high-intensity ultra-sonic bath using 18 mΩ Milli-Q® water
and dried overnight in an oven at 60º C. Core slices were then mounted into an ablation
155
cell with a motorized stage and scanned beneath a 193 nm ArF excimer laser with beam
homogenizing optics (New Wave UP-193-HE). Scan paths were selected to be parallel to
both the major growth axis of the coral, as well as to the stable isotope sampling drill path
(Fig. 4.2). At the sample surface the laser beam was 40 x 385 μm, with the long axis
oriented perpendicular to the growth axis of the coral. The laser was pulsed at 10 Hz and
between 12 and 15 J cm-2. Ablated material was carried to the plasma of a ThermoFinnigan Element 2 ICP-Sector Field MS (ICP-SFMS) with fast magnet scan and high
abundant sensitivity options via a continuous 0.8 L min-1 He stream that was mixed with
1.0 L min-1 Ar after the ablation cell. Measurements were preceded by ~10 s of
background acquisitions. Each section was scanned at a rate of approximately 20 μm/s,
with spectra being collected every 0.4 -0.7 s.
The isotopes 25Mg, 43Ca, 55Mn, 86Sr, 89Y, and 138Ba were measured with 43Ca
being used as an internal standard to correct for signal fluctuations brought about by
surface irregularity and changes in skeletal density of the coral skeleton. The ICP-SFMS
was operated in medium mass spectral resolution (R=5000) in order to completely
resolve the small 89Y+ signal from the tail of the very large 88Sr+ signal. Autolock mass
was used to minimize mass drift. Measured signal values of the minor elements 55Mn,
89
Y, and 138Ba were normalized to the measured 43Ca of the sample to give concentrations
relative to the aragonite. Each section of the Fajardo core was scanned a total of six times
along the same sampling path. The first three scans were treated as cleaning scans similar
to methods reported for other recent measurements of trace elements in coral skeletons
[e.g. Fallon et al., 1999; Alibert et al., 2003; Sinclair and McCulloch, 2004; Sinclair,
2005; Lewis et al,. 2006; Fleitmann et al., 2007]. The concentrations of each element
156
measured during scans four through six were highly reproducible (average relative
standard deviation = 6%) and data from these scans were used for data analysis.
Measurements of instrument background and known standards were collected
before and after the analysis of the coral sections in order to correct for any long-term
instrument drift. Synthetic glass standard reference materials (SRMs) were determined to
be the most suitable for trace element quantification in corals [e.g. Craig et al., 2000;
Fallon et al., 2002; Matthews, 2007]. Two glass SRMs (NIST 610 and NIST 612) were
mounted in the ablation cell along with the coral section and each were scanned prior to,
and following, the scans made on each coral section. Trace element ratios in the form of
(M signal/Ca signal)/(M mmoles/Ca moles) were determined from NIST 610 and NIST
612 standards, where M is the element of interest. M/Ca concentration ratios were
calculated from 4-point smoothed intensities of M and 43Ca based on the “recommended”
values of Pearce et al. [1997]. Drift in relative sensitivities was typically below 10%.
Signal to blank ratios were typically higher than 100:1 for 43Ca+, 86Sr+ and 138Ba+. Signal
to blank ratios were typically higher than 50:1 for 25Mg+, 55Mn+ and 89Y+.
Sampling and measurement of trace elements in ambient waters
Ambient river and seawater samples were collected for trace element analysis
along a transect from upriver to the reef at Cayo Ahogado (Fig. 4.1B) on 19 March 2008.
Samples were collected by hand from sub-surface waters (10 to 20 cm) in pre-cleaned
low-density polyethelene bottles (LDPE) at each site along the transect. Samples were
stored cold (~4º C) and in the dark while in the field, and then filtered and acidified
within 4 days upon return to the laboratory. In the laboratory, water samples were
157
handled using Nitrile™ polyethelyne gloves and filtered and acidified in a Class 100
laminar flow hood. Filtration towers were pre-cleaned with 18 mΩ Milli-Q® water and
fitted with Nucleopore™ polycarbonate membrane filters (0.4 µm pore size). Samples
were acidified to 2% (v/v) using VERITAS® double-distilled HNO3 (GFS Chemicals,
Inc.).
Low-salinity (< 5) water samples were measured undiluted using a PerkinElmer
Sciex ELAN 6000 ICP-MS. External standard solutions with known concentrations of
dissolved Ba, Mn, and Y were used for calibration. An independent check standard was
measured after every three samples to allow for correction of instrumental drift and
calculation of precision. Ca and Mn signals were normalized to the signal from Sc that
was added at 10 ppb as an internal standard. The Y signal was normalized to the signal
from In that was added at 10 ppb as an internal standard.
Samples having salinities greater than 5 were diluted by a factor of ten and the
concentrations of Ca, Ba, Mn, and Y were measured using a Thermo-Finnigan Element 2
ICP-SFMS. A duplicate Fajardo Reef sample spiked with two different concentrations of
Ba, Mn, Y and Ca was used as a standard for addition calibration [Thomas, 2003] of the
measurements. Mn+, Y+ and Ba+ were measured in low resolution mode (R=400). Sc (1
ppb) was used as an internal standard for Mn. Indium (In, 1 ppb) was used as an internal
standard for Y and Ba. Ca+ was measured in medium resolution mode (R=4000) and
normalized to the internal In standard signal. Average relative standard deviation (RSD)
values derived from repeated measurements of three check standards used to correct for
instrumental drift were 4%, and never exceeded 10%.
158
Data analysis
LA-ICP-MS data acquired for each element during each scan were converted to
an ASCII file using the Element 2 SFMS instrument software. Data for each standard
and each scan were imported into a separate spreadsheet. Data were first reduced using a
four point moving average in order to reduce the impact of peak hopping during analysis.
An average of the background signal obtained before each standard and sample
measurement was subtracted from the signals for each standard and sample. Trace
element measurements were then converted to time series using the growth chronology of
the Fajardo coral (Fig. 4.2) developed by Moyer and Grottoli [Chap. 3, this dissertation].
Trace element records were assembled using the average of three consecutive
ablation scans along the same path as described above. Averaged data from each of the
seven core sections was assembled in chronological order [see Moyer and Grottoli, Chap.
3, this dissertation] and these time series were reduced via local smoothing techniques.
All trace element records were smoothed to approximately bi-weekly resolution using
nearest neighbor running averages.
Each trace element record was then compared to river discharge data for Rio
Fajardo (USGS Station #50071000; Fig. 4.3A) obtained from the U.S. Geological Survey
[USGS, 2008]. Periodicity trends within individual data sets were examined using single
spectrum analysis based on a Fourier transform function, and co-variation and correlation
between two stochastic time series was evaluated using bivariate cross-spectral analysis
[Chatfield, 2004]. A Hamming window (width = 5) was applied to both time series.
Coherency confidence limits were estimated using the methods described by Thompson
[1979]. Smoothed data sets were detrended by subtracting the long-term average from
159
each value prior to analysis. All spectral time series analyses were performed using
Statistica version 8 (© 2007 StatSoft, Inc.) Averaged values are reported as arithmetic
means ± 1 standard deviation, and coherence was considered statistically significant at p
≤ 0.05. Conservative mixing relationships of dissolved constituents (Ba, Mn, Y) between
river and marine end-members were modeled. These models were generated by fitting a
linear trend line between the freshwater and marine end-member concentrations of each
element.
RESULTS
Coral trace elements
Measurements of the elemental ratios of Ba/Ca, Mn/Ca, and Y/Ca in the Fajardo
coral are shown in Figs. 4.3B, C, and D, respectively. Coral Ba/Ca ranged from 2.75 to
6.54 μmol mol-1 and had an overall average of 3.70 ± 0.30 μmol mol-1 (Fig. 4.3B). Over
the span of the entire record, average Ba/Ca increased by 0.224 μmol mol-1. Single
spectrum analysis showed Ba/Ca to have an annual periodicity. Annual Ba/Ca peaks
typically occurred in the latter half of each calendar year from August to January, and
were most frequent in November. Cross spectral analysis of Rio Fajardo discharge and
the Ba/Ca time series (Fig. 4.4A) revealed significant annual coherence (0.95) at the 99%
confidence limit (Fig. 4.4B). Rio Fajardo discharge and coral Ba/Ca covaried with a
nearly in-phase relationship (phase angle = 29º) with Ba/Ca lagging river discharge. The
relationship was such that as discharge increased coral Ba/Ca also increased with an
average lag of 6 ±1 weeks. Ba/Ca and δ13C anomalies in the Fajardo coral were annually
coherent (0.695) at the 80% confidence limit (Figs. 4.4C, D). Coral Ba/Ca and δ13C
160
anomalies covaried with a nearly anti-phase relationship (phase angle = 160º) such that as
Ba/Ca increased, δ13C anomalies decreased. Annual peak Ba/Ca ratios lagged the
occurrence of δ13C minima by approximately 8 ±1 weeks.
Mn/Ca ratios in the Fajardo coral ranged from 0.27 to 4.79 μmol mol-1 with an
average of 0.712 ±0.309 μmol mol-1 (Fig. 4.3C). Average Mn/Ca decreased by 0.168
μmol mol-1 over the span of the entire record. Single spectrum analysis revealed Mn/Ca to
have 2.5 yr periodicity over the entire detrended coral record. Cross spectral analysis of
Rio Fajardo discharge and the Mn/Ca time series revealed significant annual coherence at
approximately 2 year (0.736, p = 0.05) and 4.5 year (0.879, p < 0.01) intervals (Fig. 4.4E,
F).
The ratio of Y/Ca (Fig. 4.3D) in the Fajardo coral ranged from 7.39 x 10-4 to 0.29
μmol mol-1 and averaged 0.03 ± 0.02 μmol mol-1 over the span of the entire record.
Average Y/Ca remained constant for the period 1948 to 2004. Single and cross spectral
analysis of Y/Ca and Rio Fajardo discharge showed no meaningful spectral relationships
across all frequencies.
Trace elements in natural waters
The concentration of dissolved Ba ranged from 71.5 to 273.7 nmol kg-1 and was
lowest at the marine end-member site above the reef and highest at intermediate salinities
(Table 4.1). Dissolved Ba exhibited non-conservative mixing at sites with low-tointermediate salinities (Fig. 4.5A). Dissolved Mn concentrations were nearly equal at
freshwater and marine end-member sites, and Mn was more abundant by 2.5 orders of
magnitude at intermediate salinities (Table 4.1, Fig. 4.5B). As observed with Ba, this
161
high concentration at intermediate salinities was indicative of additional inputs of Mn
during mixing of river and seawater (Fig. 4.5B). Y ranged from 0.2 to 1.1 nmol kg-1 and
had the lowest concentration of all elements measured at each site (Table 4.1). The
highest Y concentration also occurred at sites with intermediate salinities and nonconservative mixing was observed (Fig. 4.5C). Dissolved Ca was the most abundant
element measured at all sites and was lowest at the river (0 salinity) end-member site and
was highest in the Bay water (Table 4.1).
Coral δ13C & Δ14C
Detailed results of the δ13C and Δ14C measurements made in the Fajardo coral
skeleton (Fig. 4.6) have previously been reported by Moyer and Grottoli [Chap. 3, this
dissertation]. Briefly, cross spectral analysis of Rio Fajardo discharge and the coral δ13C
anomalies revealed significant (p < 0.05) annual coherence such that as discharge
increased coral δ13C anomalies decreased. Coral skeletal δ13C and Δ14C anomalies were
positively correlated and synchronous depletions of both δ13C and Δ14C anomalies were
present for the periods 1950 to 1960 and again from 1975 to 2004 (Fig. 4.6). No clear
relationship was shown between the coral skeletal δ13C and Δ14C anomalies for the period
1960 to 1975, which corresponds with the timing of the maximum increase in bomb
radiocarbon within the Fajardo coral skeleton.
162
DISCUSSION
Coral Ba/Ca
Annual periodicity of Ba/Ca records in coral skeletons have been reported from a
number of studies for a variety of coral species across the Caribbean and Indo-Pacific
regions [Shen and Sanford, 1990; Shen et al., 1992a; Fallon et al., 1999; Alibert et al.,
2003; McCulloch et al., 2003; Sinclair and McCulloch, 2004; Wyndham et al., 2004].
However, the timing of annual maxima and minima can be highly variable among both
location and individual records. For corals growing inshore in non-upwelling
environments, the source of annual Ba/Ca variability in coral skeletons has been
attributed to the seasonal wet season delivery of terrigenous Ba to the coastal ocean via
rivers [Shen and Sanford, 1990; Swart et al., 1999; Alibert et al., 2003; McCulloch et al.,
2003; Sinclair and McCulloch, 2004; Fleitmann et al., 2006; Lewis et al., 2007]. Yet
other studies have reported “anomalous” Ba records from coral skeletons in coastal
waters where Ba/Ca does not reflect riverine inputs [e.g. Hart et al., 1996; Esslemont et
al., 2004; Sinclair, 2005]. In such instances, largely unspecified metabolic effects are
implicated in affecting Ba/Ca records in an unpredictable way.
The Fajardo coral was collected far from a shelf edge within a shallow, nonupwelling, semi-enclosed basin in very close proximity to the mouth of the Rio Fajardo
(Fig. 4.1). The strong coherence between Rio Fajardo discharge and coral Ba/Ca (Fig.
4.4A, B) measured in this study indicate that Ba/Ca in the Fajardo coral is influenced by
Ba being transported from land. Additionally, Ba/Ca maxima across the entire Fajardo
coral record occur near the end of each year (Figs. 4.3B), corresponding to the months of
November through January. These occurrences coincide well with the known timing of
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the wet season in the Fajardo study area (May – mid-January; Fig. 4.3A) and are lagged
by one to two months relative to the timing of average peak annual river discharge
(September – November; Fig. 4.7). The lag between peak annual river discharge and peak
Ba/Ca may be controlled by a number of factors including complex estuarine desorption
kinetics at the river mouth [Dorvall et al., 2005 and references therein], wet season
dilution effects [Alibert et al., 2003; Sinclair and McCulloch, 2004] due to Ba supply
limitations in tropical river catchments [Edmond et al., 1978; Sinclair and McCulloch,
2004], or coral metabolic and growth effects [Pingitore et al.; 1989; Matthews, 2007].
Estuarine processes influencing the concentration of dissolved Ba are known to be
complex and coastal floodplains and estuaries can serve as storage reservoirs for Ba-rich
sediments [Edmond et al., 1978; Li and Chan, 1979; Dorvall et al., 2005]. Studies in both
temperate and tropical coastal systems have identified both sporadic and gradual Ba
desorption as being a key factor in controlling the concentration of dissolved Ba in
coastal waters [Caroll et al., 1993; Coffey et al., 1997; Dorvall et al., 2005]. For example,
sediments mobilized by one large discharge event may be stored in the estuary, and then
gradual desorption by tidal mixing may produce a lag of increased coastal Ba
concentration over several days, weeks, or longer. Seasonal lags between peak discharges
(spring) and peak dissolved Ba concentrations (summer) have been reported in the
Chesapeake Bay estuary [Coffey et al., 1997; Dorvall et al., 2005]. The observed lag
between Ba/Ca and river discharge in the Fajardo coral was on the order of six weeks and
therefore could be entirely explained by sporadic release of Ba from estuarine or
floodplain-stored sediments.
164
Additionally, Ba supply to rivers via physical and chemical weathering is
typically limited in the tropics [Edmond et al., 1978] and this limited Ba supply has been
demonstrated using calibrated coral Ba/Ca records [Sinclair and McCulloch, 2004].
Alibert et al. [2003] proposed that increased precipitation and river volume could serve to
dilute this limited supply of weathered Ba in tropical rivers. Under such conditions, coral
Ba/Ca may be more reflective of cumulative, rather than instantaneous, river discharge
and associated terrestrial Ba fluxes. Ba supply to tropical rivers can also be enhanced
through increased soil respiration on land [Markewitz et al., 2001]. Thus, increased Ba
flux to the coastal ocean may not only be a product of increased river discharge, and this
may account for the lags observed between river discharge and Ba/Ca in the Fajardo
coral.
The biology of the coral may also play a role in controlling the partitioning and
apparent timing of trace element incorporation into the skeleton. Moyer and Grottoli
[Chap. 3, this dissertation] reported lower-than-normal growth rates in the Fajardo coral
and other studies have shown links between terrigenous sediment inputs to the coastal
ocean in Puerto Rico and reduced coral growth [Loya, 1976; Morelock et al., 1983;
Torres and Morelock, 2002]. Pingitore et al. [1989] have suggested that slow growth
rates in M. annularis (a sibling species of M. faveolata) may lead to lower concentrations
and less variability of skeletal Ba/Ca when compared to faster growing species. Slow
growth by the coral has also been suggested as a possible mechanism to explain observed
lags of other trace metals in high latitude [Fallon et al., 1999] and eastern Pacific corals
[Matthews, 2007]. The average growth rate of the Fajardo coral was slower than
typically observed for the species [Moyer et al., Chap. 3, this dissertation], and this could
165
also explain the lag between river discharge and Ba/Ca peaks observed in the Fajardo
coral.
Of the above-described explanations for the observed lag between Rio Fajardo
discharge and coral Ba/Ca, two seem most applicable to the Fajardo coral. Lags due to
periodic release of Ba are very likely in Fajardo due to reverse channel morphology
[Clark and Wilcock, 2000] and mangrove forests which line the Rio Fajardo estuary.
Reverse channel morphology describes a condition where river channel area and depth
decrease in the lower reaches of the catchment, closer to the river mouth. This condition
allows for more frequent over-bank flooding and increased sediment storage on the
floodplain of the Rio Fajardo [Clark and Wilcock, 2000]. Mangrove estuaries also are
very effective sediment traps and could thus store sediments before reaching the ocean.
Both of these conditions in the Rio Fajardo could cause sporadic desorption of Ba as
discussed above and could explain the observed lag between increased river discharge
and coral Ba/Ca. Biological influences are an equally likely cause for the observed lag
since the Fajardo coral also exhibited a slow rate of growth, and this has been attributed
to trace element lags in coral skeleton [Fallon et al., 1999; Matthews, 2007]. It is also
possible that both of these factors are influencing the observed Ba/Ca lag in the Fajardo
coral. However, the data presented in this study do not allow for a definitive
determination of which of the above described factors may be most influential to the
observed lag.
166
Relationship of coral Ba/Ca, δ13C, and Δ14C
Coral Ba/Ca increased as coral skeletal δ13C and Δ14C both decreased during
periods of increased Rio Fajardo discharge (Figs. 4.7 and 4.8). An inverse relationship
between Ba and δ13C was also reported in a Florida Bay coral that was thought to be
influenced by freshwater input to the coastal ocean [Swart et al., 1999]. The relationship
between coral skeletal δ13C and Δ14C and river discharge has been discussed previously
by Moyer and Grottoli [Chap. 3, this dissertation]. Their results showed that coral
skeletal δ13C decreased as Rio Fajardo discharge increased, suggesting that both δ13C and
Δ14C in the Fajardo coral reflected the delivery of δ13C- and Δ14C-depleted riverine DIC
to the coastal ocean.
Measurements of dissolved Ba from the river to the coastal ocean also support
this interpretation (Table 4.1, Fig. 4.5A). Dissolved Ba exhibited clear desorptive
behavior in the freshwater-seawater mixing zone (Fig. 4.5A). Additionally, the Ba
concentration measured in the surface waters above the reef was higher than open ocean
values reported by Shen and Sanford [1990] and Alibert et al. [2003]. These
measurements provide evidence that the riverine delivery of Ba contribute to the
concentration of dissolved Ba in the waters of Cayo Ahogado. In turn, the flux of
dissolved Ba to the coastal ocean is likely largest during the wet season, and thus is likely
driving the seasonal variability of Ba/Ca observed in the Fajardo coral skeleton (Fig. 4.3).
However, since dissolved Ba was only measured in ambient water during one dry season,
and this sampling occurred several years after the collection of the Fajardo coral, direct
calibration of riverine, seawater, and coral Ba concentrations can not be made based at
167
this time. Instead, Ba/Ca in the Fajardo coral can only provide an accurate record of the
timing and duration of increased Rio Fajardo discharge to the coastal ocean over time.
Given the strong relationship between Ba and river discharge shown here (Figs.
4.4B & 4.7) and in other recent studies [Alibert et al., 2003; McCulloch et al., 2003;
Sinclair and McCulloch, 2004; Fleitmann et al., 2006; Lewis et al., 2007], the strong
inverse relationship between between Ba/Ca and δ13C (Fig. 4.4B), and the influence of
terrestrial DIC apparent in coral skeletal δ13C and Δ14C demonstrated by Moyer and
Grottoli [Chap. 3, this dissertation], it seems likely that the coral skeletal carbon isotope
and Ba/Ca records are reflective of the chemical composition of river water as it bathes
the reef and mixes with coastal seawater. The present findings therefore support those of
Moyer and Grottoli [Chap. 3, this dissertation] by providing another independent line of
geochemical evidence that the Fajardo coral is recording riverine inputs in the form of
increased Ba and decreased δ13C and Δ14C within the coral skeleton.
Coral Mn/Ca and Y/Ca
Manganese and Yttrium in coral skeletons have also been implicated as markers
of terrigenous input to the coastal ocean [Alibert et al., 2003; Wyndham et al., 2004;
Lewis et al., 2007]. However, coral Mn/Ca has been shown to be less reflective of river
discharge and to have either no, or weak, correlation with coral Ba/Ca and/or river
discharge [Shen et al., 1992a; Alibert et al., 2003; Wyndham et al., 2004]. Additionally
coral Mn/Ca records have been shown to exhibit anomalously high, yet reproducible
peaks which do not correlate well with other trace element records within the same coral
or river discharge [Alibert et al., 2003]. Y/Ca has been shown to be correlated with (albeit
168
with less sensitivity) seasonal and long-term changes in river discharge over time [e.g.
Alibert et al., 2003; Lewis et al., 2007].
Mn/Ca in the Fajardo coral (Fig. 4.3C) did not covary with river discharge on
annual timescales (Fig. 4.4E, F). Several anomalous Mn/Ca peaks were present within the
record, and these did not consistently correspond to either peak or low-flow river
discharge periods (Fig. 4.3A, C). Coral Mn/Ca was however coherent with Rio Fajardo
discharge on 2 and 4.5 year cycles (Fig. 4.4F). This relationship between coral Mn/Ca
and river discharge suggests that Mn may be associated with terrestrial input due to
interannual tropical weather systems or climatic events. While the 2 year cyclicity does
not correspond with known climatic events, the 4.5 year periodicity falls between the
recurrence intervals of tropical storms (3 years) and minor hurricanes (6 years) in Puerto
Rico [Andrews, 2007]. This suggests that Mn may only be mobilized to the coastal ocean
when large episodic weather events cause massive increases in river discharge.
Although Mn has been used as a proxy for terrestrial sediment input to the coastal
ocean [e.g. Lewis et al., 2007], the actual source of variability of Mn/Ca ratios in coral
skeletons has remained elusive. Many studies have identified a range of possible sources
of Mn to coral skeletons including volcanic activity [Shen et al., 1991], re-suspension of
benthic sediments [Shen et al., 1992b], and terrestrial nutrient and sediment fluxes
[Alibert et al., 2003; Wyndham et al. 2004]. While Mn desorption from particulate
material is known to occur in low salinity waters in a manner similar to Ba (Fig. 4.5A,
B), the biogeochemical processes influencing Mn during and after desorption are much
more complex [Ouddane et al., 1997]. Although Mn is very sensitive to redox conditions
common in tropical mangrove-lined estuaries, it does not form a stable sulfide precipitate
169
as is common with other trace metals [Lacerda, 1997]. Ecological studies suggest Mn is
an important micro-nutrient for many marine phytoplankton and higher plants and has
been measured in high concentration compared to other trace metals in mangroves
[Lacerda, 1997] and the common tropical sea grass Thalassia testinudum [Whelan et al.,
2005]. Dissolved Mn also has a strong preference for adsorption onto carbonate particles
[Ouddane et al. 1997]. These factors may combine to explain the low concentration of
Mn measured in coastal seawater (Table 4.1) and the lack of annual coherence between
river discharge and coral Mn/Ca (Fig. 4.4F).
Y/Ca measured in the Fajardo coral was not coherent with river discharge at any
periodicity. Additionally, transient anomalous Y/Ca peaks are present throughout the
record (Fig. 4.3D) and do not correspond with similar Mn/Ca peaks or river discharge.
Alibert et al. [2003] found Y to be more enriched in coral skeletons growing near river
mouths however, the coral Y/Ca record was less sensitive to river discharge than Ba/Ca
on annual timescales. Average Y/Ca over the entire Fajardo coral record was 0.03 ±0.02
μmol mol-1, which is larger than the average reported by Alibert et al. [2003] for an
offshore coral not influenced by a river plume. Dissolved Y also exhibited nonconservative mixing, with a source of Y in the low salinity waters (Fig. 4.7), similar to
the desorptive behavior of Ba and Mn. Although this creates the potential for Y/Ca ratios
in the Fajardo coral to reflect Rio Fajardo discharge, the two time series were not
coherent nor did large Y/Ca peaks reflect times of increased river discharge (Fig. 4.3).
Although Lewis et al. [2007] were able to infer historical terrestrial sediment fluxes from
interannual coral records of Y, the annual variability of Y/Ca in corals does not appear to
accurately reflect annual patterns in river discharge.
170
Implications for proxy records
Given the strong coherence of Ba/Ca and δ13C in the coral record (Fig. 4.4D) and
the coherence of each of those geochemical records with river discharge (Fig. 4.4B)
[Moyer and Grottoli, Chap. 3, this dissertation], the combined use of Ba/Ca and carbon
isotopes (both δ13C and Δ14C) can provide a history of terrestrial river discharge and
carbon flux from land to the coastal ocean. Such a record also has implications for
reconstructing local carbon fluxes as well since coral δ13C and Δ14C are influenced by the
delivery of terrestrially derived DIC to the coastal ocean [Moyer and Grottoli, Chap. 3,
this dissertation]. Such records may be extremely useful in areas where rivers are not
gauged and land-ocean impacts are unknown.
An example of this multiple proxy for river discharge is demonstrated in Figures
4.7 and 4.8. Figure 4.7 shows coral skeletal δ13C, Δ14C, and Ba/Ca for the most recent
five years of the Fajardo coral record (1999 – 2004). This portion of the record overlaps
with available records of Rio Fajardo discharge. Where all three coral proxies are
available (1999, 2002, 2003/2004; marked by yellow vertical bars in Fig. 4.7), there is
very good agreement between the timing of increased river discharge, increased Ba/Ca
and decreases in δ13C and Δ14C. The increases in coral Ba/Ca clearly coincide with the
timing of increased Rio Fajardo discharge during the wet season as discussed above. In
addition, the depletions of δ13C and Δ14C which also are influenced by river discharge
[see discussion by Moyer and Grottoli, Chap. 3, this dissertation] are nearly synchronous
with the increases in Ba/Ca (Fig. 4.7). Because the three proxies can all be linked to
freshwater discharge and occur consistently with the same timing in the coral record, this
171
strongly suggests that the Fajardo coral is recording, with a high degree of fidelity among
the three proxies, the delivery of freshwater and terrestrial carbon to the coastal ocean.
This multi-proxy approach may be applied to a portion of the coral record where
river discharge data are not available (prior to 1961), as shown in Figure 4.8. Here, the
records of coral skeletal δ13C, Δ14C, and Ba/Ca for the period 1950 to 1956 are shown.
Where all three records are available (1950, 1955/1956), and in the absence of available
river discharge data, there is still good agreement between the timing of increased Ba/Ca
and depletions of δ13C and Δ14C. From these records it is possible to infer the
approximate timing of the wet season in each of those years (marked by vertical yellow
bars in Fig. 4.8), which also is in good agreement with the timing of the wet season
observed in Fig. 4.7 and the known long-term average occurrence of the wet season in
eastern Puerto Rico. Although it may seem possible to use only Ba/Ca and δ13C as
multiple proxies of river discharge, it is also necessary to measure Δ14C since coral
skeletal δ13C can also be influenced by metabolic processes of the coral animal [see
Moyer and Grottoli, Chap. 3, this dissertation for a more complete discussion].
Since the skeletal δ13C and Δ14C of corals growing near river mouths are
influenced by the isotopic composition of the freshwater DIC [Moyer and Grottoli, Chap.
3, this dissertation], it may be possible to use δ13C, Δ14C and Ba/Ca to reconstruct local
carbon fluxes from rivers to the coastal ocean. Additionally, since Ba/Ca has been used as
a proxy for sediment discharge, this could potentially provide a record of the delivery of
particulate organic carbon (POC) to the coastal ocean as well. Since DIC and POC
account for two of the largest carbon fluxes from tropical SMRs [Milliman and Syvitski,
1992; Lyons et al, 2002; Moyer et al., Chap. 2 this dissertation], and given the long
172
lifespan of many species of tropical coral, such a multi-proxy approach could yield
records of tropical land-ocean carbon flux spanning several centuries. Such records are
important on understanding how natural (e.g. hurricane frequency, ENSO, etc.) and
anthropogenic (e.g. deforestation, reforestation, urbanization, coastal development, etc.)
phenomena have altered tropical land-ocean carbon fluxes in the past, and also how the
fluxes of those two dominant carbon pools may respond to future changes in land-use or
climate. However, additional experimental studies in controlled environments (i.e. tank
experiments) are necessary in order to make this multi-proxy approach a fully
quantitative record of the flux of terrestrial carbon the coastal ocean. Such experiments
could use corals growing in tanks with known carbon isotope and trace element
chemistry to calibrate the resultant carbon isotope and trace element geochemistry of the
coral skeleton. With such calibration, coral records of δ13C, Δ14C and Ba/Ca could be
used as proxies for the history of land-ocean carbon flux for many areas of the tropics
where river discharge data are few, and local carbon cycling is not well understood. Such
a proxy would be extremely useful in helping to gain a clearer understanding of historical
dynamics in tropical land-ocean carbon flux in the context of modern global climate
change.
Summary
In this study, the trace elements Ba, Ca, and Y (Fig. 4.3) were measured in
combination with paired measurements of δ13C and Δ14C (Fig. 4.6) in the skeleton of a
coral growing near the mouth of a SMR in eastern Puerto Rico (Fig. 4.1). These data
revealed that Coral Ba/Ca was highly coherent with both annual river discharge and coral
173
skeletal δ13C (Fig. 4.4B, D), and that increases in coral Ba/Ca were synchronous with the
timing of depletions of both δ13C and Δ14C in the coral skeleton (Figs. 4.7 & 4.8) and
increases in river discharge (Fig. 4.7). The strong coherence between river discharge and
Ba/Ca, and the concurrent timing of increases in Ba/Ca with decreases in δ13C and Δ14C
support the hypothesis that the Fajardo coral is recording the influence of riverine waters
in the coastal ocean. Furthermore, the synchronous timing of Ba/Ca increases with
depletions of coral skeletal δ13C and Δ14C were coincident with the known wet season in
eastern Puerto Rico. These data support the hypothesis that river discharge is recorded by
multiple geochemical records, which can also be used as proxies of terrestrial carbon flux
to the coastal ocean. Of the three trace element records examined, coral Ba/Ca was the
only one to be annually coherent with river discharge. Although Mn/Ca and Y/Ca were
also expected to record river discharge, the data from the Fajardo coral did not support
this hypothesis and suggest that Mn/Ca and Y/Ca in coral skeletons are not good proxies
of annual river discharge. However, the data strongly suggest that coral skeletal records
of Ba/Ca, δ13C and Δ14C are all indicative of river discharge to the coastal ocean. With
additional experimental calibration, this combination of Ba/Ca and carbon isotopes can
be developed as proxies for the history of land-ocean carbon flux over the last several
centuries for many areas of the tropics where modern local carbon cycling is not well
understood, and historical records are scarce.
Acknowledgements: This work was supported primarily by grants to AG Grottoli from
the Andrew W. Mellon Foundation and the National Science Foundation Chemical
Oceanography Program (Grant # 0610487). RP Moyer was partially supported by an
174
OSU Presidential Fellowship and received additional funding from the American
Association of Petroleum Geologists, the American Geophysical Union, the Geological
Society of America, and the Friends of Orton Hall. We are grateful for field assistance
provided by H Anguerre, M Canals, M Cathey, C Malachowski, C Pacheco and B
Williams. RE Dodge and K Helmle facilitated the x-radiography of the coral skeletons at
the National Coral Reef Institute. Laboratory analyses were assisted by M Cathey, A
Lutton, Y Matsui, C Paver, L Swierk, and H Wu. We would like to thank B Williams and
A Shinohara for helpful discussions during the preparation of this manuscript, and xxx,
yyy, and/or anonymous persons for their careful reviews and suggestions which improved
the overall quality of the manuscript.
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TABLES
Location
Salinity
Upriver
0.1
River Mouth
11.1
Nearshore
35.8
Bay
36.1
Reef
35.5
Ba
Mn
Y
Ca
-1
-1
-1
(nmol Kg ) (nmol Kg ) (nmol Kg ) (mmol Kg-1)
176.5
7.1
0.8
0.227
273.7
217.2
1.1
1.049
174.8
8.5
0.2
0.908
72.3
9.1
0.2
1.116
71.5
8.8
0.2
1.067
Table 4.1. Trace element data in natural waters of the Fajardo study area. The
concentrations of Barium (Ba), Manganese (Mn), Yttrium (Y), and Calcium (Ca)
are given along with the salinity at each sampling site. All samples were collected
on 19 March 2008.
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FIGURES
Figure 4.1. Study area. A) Landsat 7 image of Puerto Rico, showing the location of the
Fajardo study area within Puerto Rico. B) USGS 1:24000 aerial image mosaic of the
lower Fajardo River Catchment. Orange circles indicate trace element sampling sites and
the black circle with orange ring indicates where the Fajardo coral core was collected as
well as the water sampling location over the reef at Cayo Ahogado. Landsat 7 source:
www.nasa.gov, aerial image source: www.usgs.gov.
182
Figure 4.2. X-radiograph positive prints of the Fajardo coral core. The drill paths for
stable (red lines) and radiocarbon (blue lines) isotopic analyses and laser ablation
inductively coupled plasma mass spectrometry (LA-ICP-MS) scan paths for trace
element measurement (yellow lines) are shown. The age model based on annual bands is
displayed along the right side of each core section.
183
Figure 4.3. River discharge and coral trace element ratio time series A) Rio Fajardo
discharge for the period 1961 – 2004, B) coral Ba/Ca, C) coral Mn/Ca, and D) coral
Y/Ca. All data have been smoothed to approximately bi-weekly resolution. Rio Fajardo
discharge data obtained from http://pr.water.usgs.gov.
184
185
Spectral Density
0.0
0.2
0.4
0.6
0.8
1.0
-2
0
2
4
6
8
10
B
A
1
Ba/Ca vs. Discharge
0.1 10
D
C
Period (years)
1
Ba/Ca vs. δ13C
0.1 10
F
E
1
0.1
95%
99%
Co-Spectral Density
Cross Quadrature Density
Cross Periodogram
Mn/Ca vs. Discharge
185
Figure 4.4. Results of cross spectral analysis. A) Spectral density estimates of coral Ba/Ca and Rio Fajardo discharge time
series and B) their coherence. C) Spectral density estimates of Ba/Ca and coral δ13C time series and D) their coherence. E)
Spectral density analysis of Mn/Ca and Rio Fajardo discharge time series and F) their coherence.
Squared Coherency
-1
Ba concentration (nmol Kg )
300
200
150
100
50
-1
Mn concentration (nmol Kg )
0
250
B
200
150
100
50
0
1.5
C
-1
Y Concentration (nmol Kg )
A
250
1.0
0.5
0.0
0
10
20
30
40
Salinity
Figure 4.5. Concentrations of A) Barium, B) Manganese, and C) Yttrium along a salinity
gradient from the Rio Fajardo to the coastal ocean. Theoretical conservative mixing is
shown by the dashed lines.
186
15
10
5
0
0
-5
14
Δ C anomalies (‰)
13
δ C anomalies (‰)
1
-1
-10
13
δ C anomalies
14
Δ C anomalies
-2
-15
1960
1970
1980
1990
2000
Year
Figure 4.6. Stable- (δ13C, ●) and radiocarbon (Δ14C, ▲) isotope anomalies in the Fajardo
coral skeleton for the period 1955 - 2004. δ13C anomalies were generated by removing
the trend of the 13C Suess Effect, Δ14C anomalies were generated by removing the trend
of the bomb radiocarbon curve. Figure from Moyer and Grottoli [Chap. 3, this
dissertation]
187
Figure 4.7. Fajardo coral δ13C (▬) and Δ14C anomalies (▬), Ba/Ca (▬), and Rio
Fajardo discharge (▬) from 1999 to 2004. Coral δ13C and Δ14C anomaly axes have been
inverted to aid with visual interpretation. Yellow vertical bars indicate the wet season for
years where data for all three geochemical proxies and river discharge are present. Rio
Fajardo discharge data obtained from http://pr.water.usgs.gov
188
Figure 4.8. Fajardo coral δ13C (▬) and Δ14C anomalies (▬), and Ba/Ca (▬) from 1950
to 1956. Coral δ13C and Δ14C anomaly axes have been inverted to aid with visual
interpretation. Yellow vertical bars indicate the approximate wet season during years
where data for all three geochemical proxies are present.
189
CHAPTER 5
SUMMARY AND FUTURE RESEARCH
The goals of this research were: 1) To characterize the carbon isotope signature of
agricultural and forested tropical small mountainous river (SMR) catchments and
adjacent coastal waters within Puerto Rico, 2) examine a long-term, high-resolution
record of the stable (δ13C) and radiocarbon (Δ14C) isotopes recorded in the skeleton of a
coastal coral over the past half century, and 3) use coral stable (δ13C) and radiocarbon
(Δ14C) isotopes and trace elements (Ba/Ca, Mn/Ca, Y/Ca) as multiple records of river
discharge to the coastal ocean as preserved in coral skeletons. The major findings of this
dissertation were:
1) The riverine concentration of dissolved inorganic carbon (DIC) was significantly
higher in the agricultural catchment. Dissolved and particulate organic carbon (DOC
and POC, respectively) concentrations were highly variable with respect to catchment
(agriculture vs. forested), season (wet vs. dry), and salinity (freshwater vs. marine).
The oxidation of organic matter (OM) contributed to the riverine DIC pool in both
catchments, however DIC was modern while the DOC and POC exported to the
coastal ocean was highly aged. The oldest riverine DOC was strongly influenced by
190
highly aged effluent of irrigation drainage in the agricultural catchment. Organic
carbon in coastal waters was more reflective of terrestrial sources during times of
peak river discharge, indicating that tropical SMRs may transport unaltered organic
carbon to the coastal ocean during times of increased river discharge. In the forested
catchment land-ocean carbon flux was regulated by seasonal river discharge, and
hence precipitation.
2) Synchronous depletions of both δ13C and Δ14C in the Fajardo coral skeleton are
annually coherent with the timing of peak Rio Fajardo discharge and the influx of
δ13C- and Δ14C-depleted riverine waters. These results suggest that coral skeletal δ13C
and Δ14C are recording the delivery of riverine DIC to the coastal ocean.
3) Increases in coral skeletal Ba/Ca were annually coherent with increases in river
discharge and decreases in coral skeletal δ13C. Measurements of Mn/Ca and Y/Ca in
the same coral skeleton were not annually coherent with river discharge or coral
skeletal δ13C. The strong coherence between river discharge and Ba/Ca, and the
concurrent timing of increases in Ba/Ca with decreases in δ13C and Δ14C suggest that
river discharge is simultaneously recorded by multiple geochemical records, some of
which can also be used as proxies of terrestrial carbon flux to the coastal ocean.
ISOTOPIC CHARACTER AND CONCENTRATION OF CARBON DELIVERED TO THE
TROPICAL COASTAL OCEAN BY SMALL MOUNTAINOUS RIVERS
The study presented in Chapter 2 represents a first-order comprehensive analysis
of the isotopic (δ13C and Δ14C) character and concentration of the three major carbon
191
pools transported to the coastal ocean via tropical SMRs. The follwing hypotheses were
tested: H1) Riverine DIC, DOC, and POC δ13C and values are lower and ∆14C values are
higher (younger) in water samples from reforested catchments (Fajardo) than in samples
from agricultural catchments (Guanica), and H2) Seawater DIC-, DOC-, and POC-δ13C
and -∆14C values are both lower in coastal waters during the wet season compared to the
dry season. For all cases except DI-∆14C, H1 was rejected and no statistical differences
existed between the isotopic character of DIC, DOC or POC in Guanica and Fajardo were
evident. In the case of DI-∆14C H1 was accepted since Guanica (agricultural) had
significantly lower DI-∆14C values than Fajardo (forested). H2 was rejected in all cases
with no significant seasonal differences between seawater δ13C and ∆14C for DIC, DOC,
or POC.
Since H1 and H2 were rejected for most carbon and isotope pools, the results
suggest that the concentration and isotopic character of the organic carbon pools (DOC
and POC) can be highly variable between study area, season, and year. The results also
show that the concentration and isotopic character of tropical SMRs is highly dependent
on the sources of organic material being transported to the river in individual catchments,
and the natural processes which influence the delivery of this source material to tropical
SMRs. For instance, Guanica had the oldest riverine DOC measured in either study area,
and this is apparently derived from aged irrigation effluent draining anthropogenically
disturbed agricultural lands. Additionally, single samples from single years can not
effectively capture the range of natural variability of tropical SMRs. Therefore, higher
frequency sampling (~monthly) in consecutive years is likely needed for tropical SMRs,
192
in order to best constrain the range of natural variability in the quantity, isotopic character,
and flux of terrestrial carbon to the coastal ocean in these systems.
While DIC exported to the coastal ocean was modern, the exported organic
carbon was aged, and the DOC pool in Guanica was older than all but one large
temperate or tropical river where DOC ages have been reported. Anthropogenic
disturbance is largely attributable as the reason for this, where the oldest DOC was
measured directly in irrigation drainage effluent waters and at river site downstream of
this input of irrigation effluent in the primarily agricultural Guanica study area.
Conversely, the Fajardo study area which is has less agricultural disturbance had younger
DOC that was more reflective of other temperate and tropical river systems. The isotopic
character of organic carbon in riverine, brackish, and marine waters suggested that during
times of increased river discharge, terrestrial carbon may be transported to the coastal
ocean without experiencing intense biogeochemical turnover and alteration in estuarine
waters.
CORAL RECORDS OF TERRESTRIAL CARBON DELIVERY TO THE COASTAL OCEAN
The study presented in Chapter 3 gives a 56-year record of paired measurements
of δ13C and Δ14C in coral skeleton and compares them with patterns of river discharge
and δ13C and Δ14C measurements of DIC in river and coastal waters. The following
hypotheses were tested: H3) River discharge and coral skeletal δ13C values are coherent
and inversely correlated on annual timescales, H4) Coral skeletal δ13C and ∆14C are
positively correlated, and H5) δ13C and ∆14C of riverine and seawater DIC are postitively
correlated. Rio Fajardo discharge and coral skeletal δ13C were significantly coherent at
193
annual intervals and the relationship was such that as discharge increased coral δ13C
decreased. Therefore, H3 was accepted. H4 and H5 were also accepted as there was a
significant positive correlation between δ13C and ∆14C in both coral skeleton and ambient
waters in the Fajardo study area.
In Chapter 4, the coral δ13C and Δ14C record established in Chapter 3 was
compared with trace element ratios (Ba/Ca, Mn/Ca, and Y/Ca) measured in the coral
skeleton as an additional indication that the Fajardo coral was indeed recording riverine
influence in the coastal ocean. The following hypotheses were tested: H6) Coral Ba/Ca,
Mn/Ca, and Y/Ca are annually coherent and positively correlated with river discharge in
the Rio Fajardo catchment, and H7) Coral Ba/Ca, Mn/Ca, and Y/Ca are annually coherent
and inversely correlated with coral skeletal δ13C. H6 and H7 could be accepted for coral
Ba/Ca, but not for Mn/Ca and Y/Ca as only coral Ba/Ca was annually coherent with Rio
Fajardo discharge and coral skeletal δ13C. The relationships were a positive coherence
between coral Ba/Ca and Rio Fajardo discharge, and inverse coherence between coral
Ba/Ca and δ13C. Neither coral Mn/Ca nor Y/Ca was coherent with river discharge or
coral skeletal δ13C.
These data presented in Chapters 3 and 4 were used to show the influence of
riverine DIC on the geochemistry of coral skeleton. Observed synchronous depletions in
coral skeletal δ13C and Δ14C anomalies support the idea that riverine DIC, which was
depleted in both δ13C and Δ14C relative to the open ocean, is influencing the carbon
isotopic geochemistry of the coral skeleton. Furthermore, these synchronous depletions of
coral skeletal δ13C and Δ14C were coincident with the wet season timing of peak river
discharge. These data suggest that the influence of terrestrial DIC is most pronounced
194
during the tropical wet season, when river discharge is largest. The strong coherence
between river discharge and Ba/Ca, and the concurrent timing of increases in Ba/Ca with
decreases in δ13C and Δ14C add further support to the hypothesis that the Fajardo coral is
recording the influence of riverine waters in the coastal ocean. Furthermore, the
synchronous timing of Ba/Ca increases with depletions of coral skeletal δ13C and Δ14C
were coincident with the known wet season in eastern Puerto Rico. These data show that
river discharge is recorded by multiple geochemical records, which can also be used as
proxies of terrestrial carbon flux to the coastal ocean. Of the three trace element records
examined, coral Ba/Ca was the only one to be annually coherent with river discharge.
Although Mn/Ca and Y/Ca were also expected to record river discharge, the data from
the Fajardo coral did not support this hypothesis and suggest that Mn/Ca and Y/Ca in
coral skeletons are not good proxies of annual river discharge. However, the data strongly
suggest that coral skeletal records of Ba/Ca, δ13C and Δ14C are all indicative of river
discharge to the coastal ocean.
FUTURE WORK
The research presented in this dissertation has shown the isotopic character and
concentration of carbon delivered to the coastal ocean to be highly variable with respect
to study area and season. Despite this variability, nearshore corals appear to be faithful
recorders of riverine delivery of terrestrially derived DIC in the coastal ocean. These
findings bring to light the following additional questions and lines of future research:
195
1) Single samples from each season in individual years did not effectively capture the
range of natural variability of carbon pools in the two tropical SMRs studied in Puerto
Rico. Therefore, higher frequency sampling (~monthly) in consecutive years is likely
needed for tropical SMRs, in order to best constrain the range of natural variability in
the quantity, isotopic character, and flux of terrestrial carbon to the coastal ocean in
SMRs in Puerto Rico or other tropical islands.
2) Investigation of upstream and headwater regions during a single dry season greatly
enhanced the interpretation of processes influencing the downstream isotopic
character and concentration of DIC, DOC, and POC in both the Guanica and Fajardo
study areas. In addition to the increased sampling frequency recommended above,
further investigation of upstream and headwater regions, including well and soil pore
waters, during both wet and dry seasons may further reveal the processes influencing
the isotopic character and concentration of carbon delivered to the coastal ocean by
SMRs in Puerto Rico.
3) The dual carbon isotope approach employed in the Fajardo coral skeleton allowed for
a much clearer distinction between coral δ13C variability brought about by changes in
the isotopic composition of DIC and those due to metabolic effects. However,
additional controlled experimental studies are necessary in order to make this dual
carbon isotope method a fully quantitative proxy for the influence of terrestrial DIC
to the carbon isotopic signature of the coral skeleton. Such calibration would ideally
involve controlled experiments where corals are grown in tanks and the isotopic
196
compostion (δ13C & Δ14C) of DIC can be varied. This would provide direct evidence
of the influence of DIC isotopic composition on the δ13C and Δ14C of coral skeletons.
4) Similarly, the use of multi-proxy records including high-resolution (sub-annual)
measurements of δ13C, Δ14C, and Ba/Ca could help provide historical records of
riverine carbon input to reefs. Carbon isotopes reflect the delivery of DIC, while coral
Ba/Ca may bear some relation to the riverine flux of POC to the coastal ocean. In
order to make this use of multiple proxies fully quantitative, tank experiments that
control for changes in seawater DIC concentration and carbon isotopic signature
(δ13C, Δ14C), along with changes in salinity and POC and Ba/Ca concentrations are
necessary. With this additional experimental calibration, such records could be used
as proxies for the history of land-ocean carbon flux in terms of two of the largest
carbon pools delivered to the ocean via rivers.
5) The coral carbon isotope and trace element data presented in Chapters 3 and 4
strongly suggest that the Fajardo coral is recording the riverine delivery of DIC to the
coastal ocean during the wet season. However this record comes from one single
coral in one single study area. In order to determine if using δ13C, Δ14C, and Ba/Ca in
coral skeletons as proxies of riverine delivery of carbon to the coastal ocean is
applicable outside of the Fajardo study area, additional investigation of other corals
growing near river mouths in other locations is also necessary.
197
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216
APPENDIX A
RAW CORAL ISOTOPE DATA
217
Modified
Julian Date
(year)
2004.7500
2004.6250
2004.5000
2004.3750
2004.2500
2004.1250
2004.0000
2003.8750
2003.7500
2003.5500
2003.3500
2003.1500
2002.9500
2002.7500
2002.5500
2002.3500
2002.1500
2001.9500
2001.7500
2001.5837
2001.4170
2001.2503
2001.0837
2000.9167
2000.7500
2000.5500
2000.3500
2000.1500
1999.9500
1999.7500
1999.5500
1999.3500
1999.1500
1998.9500
1998.7500
1998.5500
1998.3500
1998.1500
1997.9500
1997.7500
1997.5000
1997.2500
1997.0000
1996.7500
1996.5500
1996.3500
1996.1500
Distance
downcore (mm)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
δ13C
(‰)
-0.34
-1.06
-1.47
-1.88
-2.57
-3.00
-3.12
-2.82
-1.72
-1.40
-1.49
-1.80
-2.26
-1.63
-0.84
-0.85
-1.62
-2.05
-2.11
-1.26
-0.79
-1.50
-2.69
-2.81
-2.19
-1.03
-1.07
-0.73
-1.60
-2.29
-1.66
-0.89
-0.58
-0.96
-0.77
-0.78
-1.03
-1.45
-1.84
-1.03
-0.63
-1.12
-1.72
-1.01
-0.65
-0.86
-1.84
δ13C
trend
(‰)
-1.44
-1.43
-1.43
-1.43
-1.43
-1.43
-1.42
-1.42
-1.42
-1.41
-1.41
-1.41
-1.40
-1.40
-1.40
-1.40
-1.39
-1.39
-1.38
-1.38
-1.38
-1.38
-1.37
-1.37
-1.36
-1.36
-1.36
-1.36
-1.35
-1.35
-1.35
-1.34
-1.34
-1.33
-1.33
-1.33
-1.32
-1.32
-1.32
-1.31
-1.31
-1.31
-1.30
-1.30
-1.29
-1.29
-1.29
δ13C
anomaly
(‰)
1.10
0.38
-0.03
-0.45
-1.14
-1.58
-1.69
-1.39
-0.30
0.02
-0.07
-0.39
-0.86
-0.23
0.56
0.54
-0.23
-0.66
-0.73
0.12
0.59
-0.12
-1.31
-1.44
-0.82
0.34
0.29
0.63
-0.24
-0.94
-0.31
0.45
0.76
0.38
0.56
0.54
0.29
-0.13
-0.52
0.28
0.68
0.19
-0.42
0.29
0.65
0.43
-0.55
Δ14C
(‰)
------69.5
68.4
66.8
69.1
----71.5
72.6
73.1
71.1
78.2
------------------------82.5
82.1
84.3
75.0
82.5
--------------84.4
------90.1
------92.8
Δ14C
trend
(‰)
------68.6
68.9
69.3
69.6
69.9
70.5
71.2
71.5
71.8
72.5
73.1
73.5
73.8
74.4
74.8
75.4
75.7
76.4
76.7
77.3
77.6
78.3
78.6
79.3
79.6
79.9
80.5
80.9
81.5
82.2
82.8
83.4
83.8
84.4
84.7
85.1
85.7
86.3
87.0
87.7
88.3
88.6
89.3
89.9
Δ14C
anomaly
(‰)
------0.8
-0.6
-2.5
-0.5
----0.3
1.1
1.3
-1.4
5.1
------------------------3.2
2.6
4.4
-5.5
1.6
---------------------------------
Table 5.1. Raw coral isotope data (δ13C and Δ14C) presented and discussed in Chapters 3
and 4.
218
Table 5.1 continued
1995.9500
1995.7500
1995.5500
1995.3500
1995.1500
1994.9500
1994.7500
1994.5500
1994.3500
1994.1500
1993.9500
1993.7500
1993.5500
1993.3500
1993.1500
1992.9500
1992.7500
1992.5000
1992.2500
1992.0000
1991.7500
1991.5500
1991.3500
1991.1500
1990.9500
1990.7500
1990.5500
1990.3500
1990.1500
1989.9500
1989.7500
1989.5500
1989.3500
1989.1500
1988.9500
1988.7500
1988.5000
1988.2500
1988.0000
1987.7500
1987.6071
1987.4642
1987.3213
1987.1784
1987.0355
1986.8929
1986.7500
1986.6071
1986.4642
1986.3213
1986.1784
1986.0355
1985.8929
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
-1.13
-0.48
-0.29
-0.60
-1.61
-2.32
-1.33
-0.61
-0.48
-1.04
-2.25
-1.62
-0.62
-0.90
-1.16
-1.41
-1.16
-0.85
-0.78
-1.42
-1.06
-0.58
-0.66
-0.73
-1.36
-0.59
-0.22
-1.25
-1.83
-1.73
-0.90
-0.85
-1.11
-1.66
-2.05
-1.19
-0.65
-0.63
-1.25
-1.53
-0.96
-1.34
-1.26
-1.33
-1.67
-2.28
-1.68
-0.37
-0.79
-1.00
-1.45
-2.04
-1.20
-1.28
-1.28
-1.28
-1.27
-1.27
-1.27
-1.26
-1.26
-1.26
-1.25
-1.25
-1.24
-1.24
-1.24
-1.23
-1.23
-1.22
-1.22
-1.22
-1.21
-1.21
-1.21
-1.20
-1.20
-1.20
-1.19
-1.19
-1.18
-1.18
-1.18
-1.17
-1.17
-1.17
-1.16
-1.16
-1.15
-1.15
-1.15
-1.14
-1.14
-1.14
-1.14
-1.13
-1.13
-1.13
-1.13
-1.12
-1.12
-1.12
-1.11
-1.11
-1.11
-1.11
219
0.15
0.80
0.98
0.67
-0.34
-1.06
-0.07
0.65
0.78
0.21
-1.00
-0.37
0.62
0.33
0.07
-0.18
0.06
0.37
0.44
-0.21
0.15
0.63
0.55
0.48
-0.16
0.60
0.97
-0.07
-0.65
-0.55
0.28
0.32
0.06
-0.49
-0.89
-0.03
0.50
0.52
-0.11
-0.39
0.18
-0.21
-0.13
-0.20
-0.54
-1.15
-0.56
0.75
0.33
0.11
-0.34
-0.93
-0.09
----------94.7
----------------96.9
93.8
92.5
97.3
------------------106.1
96.3
104.7
107.9
--------------------114.5
113.0
113.3
113.6
111.2
----------114.5
---
90.5
91.2
91.5
91.8
92.5
92.8
93.4
93.8
94.4
94.7
95.4
96.0
96.7
97.3
98.0
98.3
98.9
99.6
99.9
100.6
101.2
101.5
102.1
102.5
103.1
103.8
104.4
105.0
105.7
106.0
106.7
107.0
107.6
108.3
108.6
109.2
109.6
110.2
110.9
111.5
111.8
112.1
112.5
112.8
113.1
113.5
114.1
114.4
114.7
115.4
115.7
116.0
116.3
-----------------------------1.1
-4.5
-6.5
-2.3
------------------1.1
-9.5
-1.3
1.3
--------------------2.4
0.6
0.5
0.5
-2.2
---------------
Table 5.1 continued
1985.7500
1985.5837
1985.4170
1985.2503
1985.0837
1984.9167
1984.7500
1984.6071
1984.4642
1984.3213
1984.1784
1984.0355
1983.8929
1983.7500
1983.5837
1983.4170
1983.2503
1983.0837
1982.9167
1982.7500
1982.6071
1982.4642
1982.3213
1982.1784
1982.0355
1981.8929
1981.7500
1981.6071
1981.4642
1981.3213
1981.1784
1981.0355
1980.8929
1980.7500
1980.5837
1980.4170
1980.2503
1980.0837
1979.9167
1979.7500
1979.6250
1979.5000
1979.3750
1979.2500
1979.1250
1978.9900
1978.8750
1978.7500
1978.6071
1978.4642
1978.3213
1978.1784
1978.0355
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
-0.58
-0.66
-1.17
-1.49
-2.16
-2.33
-1.47
-0.94
-0.70
-0.69
-1.26
-1.78
-2.10
-1.81
-0.85
-1.19
-0.99
-1.14
-2.09
-2.19
-1.24
-0.53
-0.62
-0.47
-1.29
-2.11
-2.60
-1.64
-0.96
-1.53
-1.56
-1.54
-1.94
-1.59
-0.48
-0.07
-0.20
-0.45
-1.58
-1.72
-1.17
-0.86
-1.05
-0.74
-1.61
-1.19
-0.34
-0.46
-0.43
-0.65
-0.92
-0.51
-1.76
-1.10
-1.10
-1.10
-1.10
-1.09
-1.09
-1.09
-1.08
-1.08
-1.08
-1.08
-1.07
-1.07
-1.07
-1.07
-1.06
-1.06
-1.06
-1.06
-1.05
-1.05
-1.05
-1.05
-1.04
-1.04
-1.04
-1.03
-1.03
-1.03
-1.03
-1.03
-1.02
-1.02
-1.02
-1.01
-1.01
-1.01
-1.01
-1.00
-1.00
-1.00
-1.00
-1.00
-0.99
-0.99
-0.99
-0.99
-0.98
-0.98
-0.98
-0.98
-0.98
-0.97
220
0.52
0.44
-0.07
-0.39
-1.06
-1.24
-0.38
0.14
0.38
0.39
-0.19
-0.70
-1.02
-0.74
0.22
-0.12
0.08
-0.08
-1.03
-1.14
-0.19
0.52
0.42
0.57
-0.25
-1.07
-1.56
-0.61
0.07
-0.50
-0.54
-0.51
-0.92
-0.57
0.54
0.94
0.81
0.56
-0.58
-0.72
-0.17
0.13
-0.05
0.25
-0.61
-0.20
0.65
0.53
0.55
0.33
0.06
0.46
-0.79
--------117.9
113.8
113.3
121.5
125.0
----------------------------------125.6
----------------------136.4
129.8
135.5
-------------------------
117.0
117.3
117.6
117.9
118.3
118.6
119.2
119.6
119.9
120.5
120.8
121.2
121.5
122.1
122.5
122.8
123.1
123.4
123.8
124.4
124.7
125.0
125.4
126.0
126.4
126.7
127.0
127.3
127.6
127.9
128.3
128.6
128.9
129.2
129.9
130.2
130.5
131.2
131.5
131.8
132.1
132.5
132.8
133.1
133.4
133.7
134.1
134.4
134.7
135.0
135.4
135.7
136.0
---------0.3
-4.8
-5.9
1.9
5.1
----------------------------------------------------------4.9
-2.0
3.4
-------------------------
Table 5.1 continued
1977.8929
1977.7500
1977.5500
1977.3500
1977.1500
1976.9500
1976.7500
1976.5837
1976.4170
1976.2503
1976.0837
1975.9167
1975.7500
1975.5000
1975.2500
1975.0000
1974.7500
1974.5837
1974.4170
1974.2503
1974.0837
1973.9167
1973.7500
1973.4167
1973.0833
1972.7500
1972.6250
1972.5000
1972.3750
1972.2500
1972.1250
1972.0000
1971.8750
1971.7500
1971.5000
1971.2500
1971.0000
1970.7500
1970.5500
1970.3500
1970.1500
1969.9500
1969.7500
1969.5000
1969.2500
1969.0000
1968.7500
1968.6071
1968.4642
1968.3213
1968.1784
1968.0355
1967.8929
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
-1.82
-0.39
-0.54
-0.93
-1.45
0.09
-0.71
0.19
-0.19
-1.34
-1.97
-1.11
-0.09
-0.34
-0.61
-1.46
-1.64
-0.69
-0.76
-0.72
-1.56
-2.07
-1.22
0.01
-0.56
-1.38
-1.97
-1.47
-0.13
-0.68
-0.96
-1.97
-2.26
-1.25
0.14
-0.16
-1.05
-1.92
-0.61
-0.96
-0.75
-0.94
-1.23
-0.26
-0.88
-0.83
-1.21
-0.91
0.13
-0.64
-1.10
-1.41
-1.22
-0.97
-0.97
-0.96
-0.96
-0.96
-0.95
-0.95
-0.95
-0.94
-0.94
-0.94
-0.94
-0.93
-0.93
-0.93
-0.92
-0.92
-0.91
-0.91
-0.91
-0.90
-0.90
-0.89
-0.89
-0.89
-0.88
-0.88
-0.87
-0.87
-0.87
-0.87
-0.87
-0.86
-0.86
-0.86
-0.85
-0.85
-0.85
-0.84
-0.84
-0.84
-0.83
-0.83
-0.82
-0.82
-0.82
-0.81
-0.81
-0.80
-0.80
-0.80
-0.80
-0.79
221
-0.85
0.58
0.43
0.03
-0.49
1.04
0.24
1.14
0.76
-0.40
-1.03
-0.17
0.84
0.59
0.32
-0.53
-0.72
0.22
0.15
0.19
-0.66
-1.17
-0.33
0.90
0.33
-0.50
-1.09
-0.60
0.74
0.19
-0.09
-1.11
-1.40
-0.39
1.00
0.69
-0.20
-1.07
0.24
-0.12
0.08
-0.11
-0.40
0.57
-0.06
-0.02
-0.40
-0.11
0.93
0.17
-0.30
-0.61
-0.43
----------------------------------------------------------------156.6
143.6
---------------------------------------
136.3
136.7
137.3
137.6
138.3
138.9
139.3
139.9
140.2
140.5
140.8
141.5
141.8
142.5
143.1
143.7
144.4
145.0
145.7
146.0
146.6
147.0
147.6
148.3
148.9
149.6
150.2
150.5
150.8
151.2
151.5
151.8
152.1
143.0
139.9
136.8
133.7
132.0
129.0
127.4
124.3
122.7
119.5
116.5
113.3
110.2
106.9
103.9
102.4
100.8
97.7
96.1
94.4
----------------------------------------------------------------4.5
0.5
---------------------------------------
Table 5.1 continued
1967.7500
1967.5837
1967.4170
1967.2503
1967.0837
1966.9167
1966.7500
1966.5837
1966.4170
1966.2503
1966.0837
1965.9167
1965.7500
1965.6071
1965.4642
1965.3213
1965.1784
1965.0355
1964.8929
1964.7500
1964.6071
1964.4642
1964.3213
1964.1784
1964.0355
1963.8929
1963.7500
1963.5500
1963.3500
1963.1500
1962.9500
1962.7500
1962.5837
1962.4170
1962.2503
1962.0837
1961.9167
1961.7500
1961.6071
1961.4642
1961.3213
1961.1784
1961.0355
1960.8929
1960.7500
1960.6071
1960.4642
1960.3213
1960.1784
1960.0355
1959.8929
1959.7500
1959.5837
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
-1.51
-0.28
-0.22
-0.34
-0.54
-1.38
-1.07
0.00
0.15
-0.26
-0.72
-1.18
-1.17
-0.34
-0.40
-0.48
-0.59
-1.16
-1.61
-1.47
-0.37
-0.56
-0.54
-1.25
-1.42
-1.90
-1.76
-0.98
-0.03
-0.89
-0.83
-1.38
-1.13
0.37
-0.03
-0.55
-1.31
-1.79
-0.47
-0.16
-0.51
-0.10
-0.21
-1.04
-1.16
-0.37
-0.21
-0.21
-0.58
-1.02
-1.13
-1.00
-0.21
-0.79
-0.79
-0.79
-0.78
-0.78
-0.78
-0.77
-0.77
-0.77
-0.77
-0.76
-0.76
-0.76
-0.75
-0.75
-0.75
-0.75
-0.74
-0.74
-0.74
-0.73
-0.73
-0.73
-0.73
-0.73
-0.72
-0.72
-0.72
-0.72
-0.71
-0.71
-0.71
-0.70
-0.70
-0.70
-0.69
-0.69
-0.69
-0.68
-0.68
-0.68
-0.68
-0.68
-0.67
-0.67
-0.67
-0.66
-0.66
-0.66
-0.66
-0.65
-0.65
-0.65
222
-0.72
0.51
0.56
0.44
0.24
-0.60
-0.30
0.77
0.92
0.51
0.04
-0.42
-0.41
0.41
0.35
0.27
0.16
-0.42
-0.87
-0.73
0.36
0.17
0.20
-0.52
-0.70
-1.18
-1.04
-0.26
0.68
-0.18
-0.12
-0.68
-0.43
1.07
0.67
0.14
-0.62
-1.11
0.21
0.53
0.17
0.58
0.47
-0.37
-0.49
0.30
0.46
0.45
0.08
-0.36
-0.48
-0.35
0.44
--------------------------------------------------------------------16.7
11.7
6.8
5.3
-------------------------------
93.0
89.9
88.3
86.7
83.6
81.9
80.5
77.3
75.8
74.2
71.1
69.4
68.0
64.8
63.3
61.7
60.1
58.6
56.9
55.4
52.3
50.8
49.2
47.6
46.1
44.4
42.9
39.8
38.2
35.1
33.5
31.9
28.9
27.3
25.7
22.6
21.0
19.3
16.3
14.8
13.2
11.6
10.1
8.5
6.8
3.8
2.3
0.7
-2.4
-4.0
-5.7
-7.1
-10.3
---------------------------------------------------------------------9.1
-10.9
-14.2
-14.1
-------------------------------
Table 5.1 continued
1959.4170
1959.2503
1959.0837
1958.9167
1958.7500
1958.5837
1958.4170
1958.2503
1958.0837
1957.9167
1957.7500
1957.5000
1957.2500
1957.0000
1956.7500
1956.6071
1956.4642
1956.3213
1956.1784
1956.0355
1955.8929
1955.7500
1955.6071
1955.4642
1955.3213
1955.1784
1955.0355
1954.8929
1954.7500
1954.5500
1954.3500
1954.1500
1953.9500
1953.7500
1953.5837
1953.4170
1953.2503
1953.0837
1952.9167
1952.7500
1952.5837
1952.4170
1952.2503
1952.0837
1951.9167
1951.7500
1951.5500
1951.3500
1951.1500
1950.9500
1950.7500
1950.5000
1950.2500
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
-0.83
-0.88
-0.66
-1.35
-1.13
-1.07
-0.32
-0.21
-0.80
-1.80
-1.14
0.11
-0.12
-0.14
-0.93
-0.90
-0.35
0.01
-0.42
-0.86
-1.71
-1.30
-0.46
-0.13
0.02
-1.03
-1.11
-1.46
-0.90
-0.16
-0.13
-0.78
-1.40
-0.88
-0.42
-0.38
-0.25
-0.47
-1.06
-1.25
-0.57
-0.23
-0.35
-0.23
-0.94
-0.67
-0.31
-0.06
-0.68
-1.29
-0.92
0.08
0.44
-0.65
-0.64
-0.64
-0.64
-0.64
-0.63
-0.63
-0.63
-0.62
-0.62
-0.62
-0.61
-0.61
-0.61
-0.60
-0.60
-0.59
-0.59
-0.59
-0.59
-0.59
-0.58
-0.58
-0.58
-0.58
-0.57
-0.57
-0.57
-0.56
-0.56
-0.56
-0.55
-0.55
-0.55
-0.54
-0.54
-0.54
-0.54
-0.53
-0.53
-0.53
-0.52
-0.52
-0.52
-0.52
-0.51
-0.51
-0.51
-0.50
-0.50
-0.49
-0.49
-0.49
223
-0.18
-0.24
-0.02
-0.71
-0.49
-0.44
0.31
0.41
-0.17
-1.18
-0.53
0.73
0.48
0.47
-0.33
-0.30
0.24
0.61
0.17
-0.27
-1.12
-0.72
0.12
0.45
0.59
-0.46
-0.54
-0.89
-0.33
0.40
0.43
-0.22
-0.85
-0.33
0.13
0.16
0.29
0.06
-0.53
-0.72
-0.04
0.29
0.17
0.29
-0.42
-0.15
0.20
0.44
-0.18
-0.79
-0.43
0.57
0.93
---------------------------------46.3
-45.6
-49.2
-51.5
---------------------------------------------------------46.5
-48.9
-48.3
-49.5
-45.7
-11.8
-13.4
-14.9
-16.5
-18.2
-21.2
-22.8
-24.3
-27.5
-30.7
-32.2
-35.3
-38.4
-40.0
-43.2
-46.2
-47.8
-49.4
-52.3
-52.2
-52.1
-52.0
-51.8
-51.7
-51.5
-51.4
-51.2
-51.1
-51.0
-50.8
-50.6
-50.5
-50.2
-50.1
-49.9
-49.8
-49.7
-49.6
-49.5
-49.4
-49.1
-49.0
-48.9
-48.7
-48.6
-48.5
-48.3
-48.0
-47.8
-47.6
-47.5
-47.3
-47.1
--------------------------------6.0
6.6
2.9
0.5
--------------------------------------------------------0.6
-1.8
-1.2
-2.5
-1.2
Table 5.1 continued
1950.0000
1949.7500
1949.6071
1949.4642
1949.3213
1949.1784
1949.0355
1948.8929
1948.7500
312
313
314
315
316
317
318
319
320
-0.35
-0.74
-0.12
-0.24
-0.55
-0.68
-1.62
-1.60
-0.60
-0.48
-0.48
-0.47
-0.47
-0.47
-0.47
-0.46
-0.46
-0.46
224
0.13
-0.26
0.35
0.23
-0.09
-0.22
-1.15
-1.14
-0.14
---------------45.2
-45.2
-46.8
-46.6
-46.4
-46.3
-46.2
-46.1
-46.0
-45.9
-45.8
--------------0.7
0.6
APPENDIX B
HIGH RESOLUTION CORAL STABLE ISOTOPE DATA
225
Modified
Julian
Date
(year)
2004.150
2004.138
2004.125
2004.113
2004.100
2004.088
2004.075
2004.063
2004.050
2004.038
2004.025
2004.013
2004.000
2003.988
2003.975
2003.963
2003.950
2003.938
2003.925
2003.913
2003.900
2003.888
2003.875
2003.863
2003.850
2003.838
2003.825
2003.813
2003.800
2003.788
2003.775
2003.763
2003.750
2003.730
2003.710
2003.690
2003.670
2003.650
2003.630
2003.610
2003.590
2003.570
Distance
downcore
(mm)
4.8
4.9
5.0
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
6.0
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
7.0
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
8.0
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
δ13C
(‰)
-1.83
-2.24
-2.32
-2.00
-2.22
-2.18
-2.02
-2.99
-2.80
-2.55
-2.63
-2.52
-3.20
-2.99
-3.02
-3.31
-2.94
-2.92
-3.14
-3.09
-2.77
-2.77
-2.23
-1.70
-1.34
-1.18
-0.84
-1.02
-0.86
-0.49
-0.72
-0.80
-0.83
-1.03
-0.80
-0.92
-0.71
-0.92
-0.97
-1.01
-0.96
-0.68
δ13C
trend
(‰)
-1.43
-1.43
-1.43
-1.43
-1.43
-1.43
-1.43
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
-1.42
δ13C
anomaly
(‰)
-0.41
-0.82
-0.90
-0.58
-0.80
-0.75
-0.60
-1.57
-1.37
-1.12
-1.20
-1.10
-1.77
-1.57
-1.60
-1.89
-1.52
-1.49
-1.71
-1.67
-1.35
-1.35
-0.81
-0.28
0.08
0.25
0.58
0.40
0.56
0.93
0.70
0.62
0.59
0.39
0.62
0.50
0.71
0.50
0.45
0.41
0.46
0.74
Table 6.1. Stable carbon isotope (δ13C) data analyzed at high resolution
(0.1 mm) and discussed in Chapter 3.
226
Table 6.1 Continued
2003.550
2003.530
2003.510
2003.490
2003.470
2003.450
2003.430
2003.410
2003.390
2003.370
2003.350
2003.330
2003.310
2003.290
2003.270
2003.250
2003.230
2003.210
2003.190
2003.170
2003.150
2003.130
2003.110
2003.090
2003.070
2003.050
2003.030
2003.010
2002.990
2002.970
2002.950
2002.930
2002.910
2002.890
2002.870
2002.850
2002.830
2002.810
2002.790
2002.770
2002.750
2002.730
2002.710
2002.690
2002.670
2002.650
2002.630
2002.610
2002.590
2002.570
2002.550
2002.530
2002.510
9.0
9.1
9.2
9.3
9.4
9.5
9.6
9.7
9.8
9.9
10.0
10.1
10.2
10.3
10.4
10.5
10.6
10.7
10.8
10.9
11.0
11.1
11.2
11.3
11.4
11.5
11.6
11.7
11.8
11.9
12.0
12.1
12.2
12.3
12.4
12.5
12.6
12.7
12.8
12.9
13.0
13.1
13.2
13.3
13.4
13.5
13.6
13.7
13.8
13.9
14.0
14.1
14.2
-0.82
-0.99
-1.24
-0.95
-0.88
-1.02
-1.01
-1.08
-1.12
-1.25
-1.49
-1.60
-1.75
-1.71
-1.99
-1.99
-2.06
-1.95
-2.00
-1.94
-2.47
-1.90
-2.00
-2.10
-2.12
-2.19
-3.01
-2.27
-2.36
-1.77
-1.46
-1.80
-1.60
-1.75
-1.54
-1.34
-1.50
-0.95
-1.05
-0.52
-0.25
-0.29
-0.18
-0.09
0.12
-0.11
-0.18
-0.05
-0.42
-0.49
-0.67
-0.56
-0.53
227
-1.42
-1.42
-1.42
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.41
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
0.59
0.43
0.17
0.46
0.53
0.39
0.41
0.33
0.30
0.16
-0.07
-0.18
-0.34
-0.30
-0.58
-0.58
-0.65
-0.54
-0.59
-0.54
-1.06
-0.50
-0.60
-0.70
-0.71
-0.78
-1.60
-0.87
-0.96
-0.36
-0.05
-0.40
-0.19
-0.35
-0.14
0.06
-0.10
0.45
0.36
0.88
1.16
1.11
1.22
1.31
1.52
1.29
1.22
1.35
0.98
0.91
0.73
0.83
0.87
Table 6.1 Continued
2002.490
2002.470
2002.450
2002.430
2002.410
2002.390
2002.370
2002.350
14.3
14.4
14.5
14.6
14.7
14.8
14.9
15.0
-0.59
-0.60
-0.48
-0.37
-0.38
-0.47
-1.37
-0.58
228
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.40
-1.39
0.81
0.80
0.92
1.03
1.02
0.92
0.02
0.81
APPENDIX C
BI-WEEKLY SMOOTHED RIVER DISCHARGE AND CORAL TRACE
ELEMENT DATA
229
Modified
Julian Date
(year)
2004.7623
2004.7238
2004.6853
2004.6468
2004.6084
2004.5699
2004.5314
2004.4929
2004.4545
2004.4160
2004.3775
2004.3390
2004.3006
2004.2621
2004.2236
2004.1851
2004.1467
2004.1082
2004.0697
2004.0312
2003.9928
2003.9543
2003.9158
2003.8773
2003.8389
2003.8004
2003.7619
2003.7235
2003.6850
2003.6465
2003.6080
2003.5696
2003.5311
2003.4926
2003.4541
2003.4157
2003.3772
2003.3387
2003.3002
2003.2618
2003.2233
2003.1848
2003.1463
2003.1079
2003.0694
2003.0309
2002.9924
Rio Fajardo
Discharge
(m3 s-1)
3.0846
3.0846
3.0846
3.0846
3.0846
3.0846
3.0846
3.0653
2.8119
2.5584
2.8350
2.7935
2.7781
2.7628
2.7322
2.6945
2.7189
2.4649
1.8705
2.1200
2.3696
3.2349
2.9721
3.0266
3.3318
3.4982
3.4927
3.4872
3.4762
3.4496
3.1660
2.2615
1.6027
1.5482
1.4937
2.0688
1.9122
1.8322
1.7522
1.6504
1.6037
1.5569
1.7102
1.6100
1.5611
1.5254
0.7675
Ba/Ca
(μmol mol-1)
4.1476
3.7803
3.6261
3.6300
3.6362
3.5699
3.6399
3.7757
3.7840
3.8055
3.9418
4.0662
4.1371
4.1034
4.3477
4.4015
4.7422
5.1200
4.9841
4.8990
4.3781
4.1769
4.0771
4.0972
4.0212
4.0437
4.0159
3.9367
3.9079
3.8806
3.8065
3.7779
3.7544
3.7324
3.7511
3.7864
3.7525
3.7163
3.6393
3.6247
3.5973
3.6786
3.6446
3.6626
3.7145
3.7479
3.7738
Mn/Ca
(μmol mol-1)
Y/Ca
(μmol mol-1)
1.0532
1.1409
0.7870
0.7412
0.7618
0.6543
0.6986
0.7366
0.6226
0.6202
0.6691
0.7545
0.7556
0.7190
0.6746
0.6936
0.8219
0.9159
0.9625
1.0740
0.7378
0.6050
0.5532
0.5970
0.5773
0.5710
0.5964
0.5959
0.5754
0.5673
0.6018
0.6020
0.6179
0.6108
0.6661
0.7770
0.7001
0.6692
0.6238
0.5815
0.5286
0.4483
0.4004
0.3851
0.3854
0.3843
0.3819
Table 7.1. Bi-weekly smoothed Rio Fajardo discharge and coral trace
element data presented and discussed in Chapter 4.
230
0.0246
0.0423
0.0309
0.0273
0.0217
0.0266
0.0213
0.0244
0.0251
0.0280
0.0247
0.0231
0.0244
0.0308
0.0282
0.0283
0.0330
0.0401
0.0449
0.0662
0.0413
0.0336
0.0286
0.0232
0.0222
0.0273
0.0325
0.0344
0.0350
0.0333
0.0284
0.0284
0.0261
0.0333
0.0444
0.0389
0.0370
0.0485
0.0411
0.0331
0.0360
0.0241
0.0193
0.0156
0.0148
0.0165
0.0149
Table 7.1 continued
2002.9540
2002.9155
2002.8770
2002.8385
2002.8001
2002.7616
2002.7231
2002.6847
2002.6462
2002.6077
2002.5692
2002.5308
2002.4923
2002.4538
2002.4153
2002.3769
2002.3384
2002.2999
2002.2614
2002.2230
2002.1845
2002.1460
2002.1075
2002.0691
2002.0306
2001.9921
2001.9536
2001.9152
2001.8767
2001.8382
2001.7997
2001.7613
2001.7228
2001.6843
2001.6458
2001.6074
2001.5689
2001.5304
2001.4920
2001.4535
2001.4150
2001.3765
2001.3381
2001.2996
2001.2611
2001.2226
2001.1842
2001.1457
2001.1072
2001.0687
2001.0303
2000.9918
2000.9533
0.8192
0.8710
1.0570
1.1223
1.1876
1.2377
1.1469
1.1665
1.1862
1.1160
1.1710
1.4527
1.4843
1.4819
1.4808
1.4796
1.6991
1.7594
1.6626
1.6350
1.6686
1.7184
1.7682
1.5261
2.0132
2.0090
2.0048
2.3849
2.3725
2.3601
2.4757
2.4864
2.4970
2.5189
2.5049
2.4979
2.4908
2.3533
1.7054
1.5771
0.8805
0.8143
0.8841
0.9538
0.9599
0.9660
0.9710
0.9760
0.8323
0.8431
0.8539
0.8954
0.8486
3.7480
3.7489
3.7369
3.7534
3.7044
3.6962
3.7624
3.6880
3.7316
3.7102
3.7444
3.5930
3.5719
3.5748
3.5027
3.4798
3.5403
3.6052
3.6319
3.6979
3.8090
3.8625
4.0620
4.0307
3.9744
3.9867
3.9724
3.8734
3.8510
3.8400
3.7703
3.7747
3.7542
3.5676
3.4520
3.4290
3.6070
3.5863
3.6856
3.6466
3.7320
3.7627
3.7669
3.9682
3.7517
3.7718
3.7928
3.8943
4.0004
4.0839
4.0980
4.0756
3.8919
231
0.3840
0.3881
0.3731
0.3716
0.3948
0.4056
0.3996
0.4057
0.4025
0.3905
0.4178
0.4512
0.4831
0.4773
0.4755
0.4661
0.4704
0.4442
0.4245
0.4113
0.3604
0.3721
0.3742
0.3746
0.4240
0.3979
0.4267
0.4278
0.4567
0.4964
0.5108
0.5118
0.5086
0.4817
0.5371
0.5342
0.5655
0.5909
0.5920
0.5140
0.5179
0.4311
0.3704
0.4181
0.4269
0.3923
0.3766
0.3608
0.3706
0.4181
0.4699
0.4587
0.5001
0.0170
0.0173
0.0184
0.0173
0.0165
0.0174
0.0186
0.0199
0.0198
0.0243
0.0179
0.0224
0.0217
0.0195
0.0163
0.0179
0.0209
0.0198
0.0163
0.0176
0.0197
0.0200
0.0222
0.0246
0.0239
0.0268
0.0272
0.0298
0.0277
0.0249
0.0243
0.0268
0.0249
0.0206
0.0209
0.0163
0.0203
0.0204
0.0231
0.0276
0.0231
0.0180
0.0200
0.0245
0.0291
0.0245
0.0241
0.0279
0.0313
0.0246
0.0218
0.0180
0.0180
Table 7.1 continued
2000.9148
2000.8764
2000.8379
2000.7994
2000.7609
2000.7225
2000.6840
2000.6455
2000.6070
2000.5686
2000.5301
2000.4916
2000.4532
2000.4147
2000.3762
2000.3377
2000.2993
2000.2608
2000.2223
2000.1838
2000.1454
2000.1069
2000.0684
2000.0299
1999.9915
1999.9530
1999.9145
1999.8760
1999.8376
1999.7991
1999.7606
1999.7221
1999.6837
1999.6452
1999.6067
1999.5682
1999.5298
1999.4913
1999.4528
1999.4143
1999.3759
1999.3374
1999.2989
1999.2605
1999.2220
1999.1835
1999.1450
1999.1066
1999.0681
1999.0296
1998.9911
1998.9527
1998.9142
0.8339
0.8192
0.8853
0.8163
0.7473
0.7921
0.7926
0.7931
1.0277
1.1769
1.3561
1.5354
1.6390
1.5937
1.5521
1.5105
1.5008
1.5364
1.5719
1.6479
1.4058
1.2184
0.8289
0.7654
0.7967
0.8280
0.8570
0.8859
1.0049
1.0723
1.6426
2.3993
3.1560
3.5243
3.9446
4.3063
4.6112
4.9544
4.9487
4.9430
4.9316
4.8436
4.1438
2.7752
2.4609
2.2886
2.1163
1.7249
1.5765
1.4282
1.0740
0.9202
0.9183
3.7455
3.8149
3.8450
3.8396
3.8914
3.8380
3.7648
3.8389
3.5600
3.4709
3.4162
3.4138
3.4533
3.5202
3.6604
3.8297
3.7370
3.8155
3.9165
4.0062
3.9884
3.9928
3.9617
4.2728
4.0486
4.1378
4.2097
4.1304
4.2521
4.1478
4.0379
3.7530
3.5743
3.4928
3.4799
3.4425
3.5521
3.5519
3.5928
3.6098
3.5929
3.5813
3.5575
3.5444
3.5828
3.6182
3.5732
3.5527
3.6022
3.7043
3.7047
3.7488
3.8321
232
0.4783
0.5214
0.5544
0.5774
0.5772
0.7335
0.6306
0.5022
0.5361
0.5455
0.5703
0.5945
0.5958
0.5588
0.5164
0.4566
0.4192
0.4493
0.4441
0.4657
0.4184
0.3747
0.3414
0.4188
0.4176
0.3775
0.3896
0.3901
0.4216
0.4793
0.5728
0.4469
0.4471
0.4696
0.4701
0.4662
0.6168
0.6545
0.6959
0.9204
1.1138
1.0409
0.7375
0.5942
0.5997
0.5857
0.5138
0.4897
0.4589
0.4391
0.4050
0.3877
0.3460
0.0191
0.0184
0.0161
0.0183
0.0201
0.0219
0.0209
0.0275
0.0213
0.0267
0.0283
0.0212
0.0207
0.0212
0.0215
0.0241
0.0226
0.0202
0.0205
0.0192
0.0256
0.0623
0.0520
0.0592
0.0396
0.0461
0.0489
0.0366
0.0333
0.0290
0.0239
0.0182
0.0156
0.0133
0.0161
0.0145
0.0144
0.0135
0.0139
0.0147
0.0119
0.0129
0.0128
0.0136
0.0139
0.0118
0.0109
0.0127
0.0129
0.0136
0.0139
0.0154
0.0194
Table 7.1 continued
1998.8757
1998.8372
1998.7988
1998.7603
1998.7218
1998.6833
1998.6449
1998.6064
1998.5679
1998.5294
1998.4910
1998.4525
1998.4140
1998.3755
1998.3371
1998.2986
1998.2601
1998.2216
1998.1832
1998.1447
1998.1062
1998.0678
1998.0293
1997.9908
1997.9523
1997.9139
1997.8754
1997.8369
1997.7984
1997.7600
1997.7215
1997.6830
1997.6445
1997.6061
1997.5676
1997.5291
1997.4906
1997.4522
1997.4137
1997.3752
1997.3367
1997.2983
1997.2598
1997.2213
1997.1828
1997.1444
1997.1059
1997.0674
1997.0290
1996.9905
1996.9520
1996.9135
1996.8751
0.9164
0.9125
1.2265
1.5883
1.7966
2.6989
2.8643
3.0298
3.7062
3.8466
3.9869
4.4373
4.6621
4.6287
4.5954
4.5287
4.1214
4.0280
3.1589
3.2030
2.9072
2.6114
2.5197
2.4279
2.2017
1.8454
1.8555
1.8194
1.7834
1.8519
2.0349
1.8954
1.8408
2.3309
2.3416
2.3522
2.3734
2.7593
2.9806
3.0193
2.9896
2.9598
2.7390
2.6456
2.4736
1.9481
1.8308
1.7721
1.7135
1.4862
1.2590
0.9371
0.9788
4.0157
4.0517
4.0259
4.0871
4.1251
3.9759
3.7910
3.3526
3.3911
3.5676
3.6022
3.5706
3.6612
3.6309
3.5771
3.5415
3.4452
3.4985
3.7076
3.6673
3.7270
3.6834
3.6261
3.6641
3.6102
3.5842
3.7859
3.7604
3.6869
3.6708
3.7434
3.6125
3.4845
3.3074
3.3222
3.3524
3.3242
3.3767
3.4144
3.4522
3.5121
3.7592
3.8180
3.7143
3.7497
3.9416
4.0776
4.0100
3.8506
3.8659
4.0379
4.0357
4.0483
233
0.3779
0.3799
0.3812
0.3767
0.4164
0.4528
0.4724
0.4486
0.6080
0.6540
0.6108
0.5875
0.5758
0.5844
0.5359
0.5366
0.5247
0.5099
0.6392
0.5019
0.5026
0.5273
0.5248
0.4780
0.4818
0.5078
0.5641
0.5118
0.5330
0.5647
0.6184
0.5764
0.5101
0.4577
0.5120
0.5361
0.5614
0.6093
0.6196
0.5836
0.5624
0.5378
0.4723
0.3969
0.3850
0.4135
0.4130
0.4257
0.4211
0.4592
0.4463
0.3861
0.3963
0.0293
0.0302
0.0314
0.0302
0.0305
0.0336
0.0280
0.0236
0.0189
0.0237
0.0316
0.0205
0.0447
0.0358
0.0180
0.0154
0.0181
0.0200
0.0241
0.0247
0.0261
0.0254
0.0245
0.0192
0.0174
0.0186
0.0252
0.0243
0.0264
0.0219
0.0255
0.0289
0.0215
0.0136
0.0128
0.0133
0.0113
0.0125
0.0119
0.0118
0.0118
0.0142
0.0147
0.0178
0.0169
0.0189
0.0208
0.0272
0.0272
0.0289
0.0311
0.0343
0.0349
Table 7.1 continued
1996.8366
1996.7981
1996.7596
1996.7212
1996.6827
1996.6442
1996.6057
1996.5673
1996.5288
1996.4903
1996.4518
1996.4134
1996.3749
1996.3364
1996.2979
1996.2595
1996.2210
1996.1825
1996.1440
1996.1056
1996.0671
1996.0286
1995.9901
1995.9517
1995.9132
1995.8747
1995.8363
1995.7978
1995.7593
1995.7208
1995.6824
1995.6439
1995.6054
1995.5669
1995.5285
1995.4900
1995.4515
1995.4130
1995.3746
1995.3361
1995.2976
1995.2591
1995.2207
1995.1822
1995.1437
1995.1052
1995.0668
1995.0283
1994.9898
1994.9513
1994.9129
1994.8744
1994.8359
0.8625
0.8637
0.8649
0.8885
1.2165
1.2690
1.3635
1.4701
2.0565
2.1367
2.2169
2.2252
2.2235
2.2218
2.8303
2.7462
2.7037
2.6611
2.7515
2.7410
2.7305
2.3659
2.1415
2.2828
2.2827
2.2826
2.2823
1.5473
1.4133
1.5404
1.3126
1.5491
1.7856
1.7918
2.1342
1.9904
2.1198
2.2594
2.3192
2.3491
2.3790
2.7335
2.7591
2.3433
2.3335
2.0582
2.0582
2.0582
2.1573
2.2564
2.2167
1.9866
1.5182
4.0306
4.0797
3.9716
3.7049
3.7613
3.5405
3.5341
3.5039
3.3182
3.4622
3.3999
3.3522
3.4234
3.4184
3.5126
3.5205
3.4804
3.3998
3.3669
3.3964
3.4755
3.5291
3.5602
3.5656
3.5804
3.7296
3.8343
3.9630
4.0145
3.7851
3.7090
3.6909
3.7019
3.5810
3.5459
3.4000
3.3571
3.3549
3.5519
3.6638
3.7148
3.7872
3.8645
3.9298
4.0195
4.2024
4.1999
4.4802
4.1855
4.1167
4.1050
4.0659
4.0851
234
0.4004
0.4283
0.8838
0.5077
0.5603
0.5768
0.7102
0.6691
0.6461
0.6671
0.7970
0.6870
0.6760
0.6684
0.6275
0.5717
0.5298
0.5287
0.5186
0.4920
0.4890
0.4773
0.4838
0.5062
0.5263
0.4518
0.4428
0.5008
0.5381
0.4772
0.4445
0.4313
0.5024
0.5302
0.5459
0.6438
0.7244
0.6563
0.6241
0.6405
0.6067
0.5564
0.5442
0.5717
0.5853
0.6679
0.6402
0.9162
0.6732
0.6530
0.7277
0.7596
0.8678
0.0369
0.0397
0.0333
0.0179
0.0172
0.0142
0.0165
0.0535
0.0149
0.0164
0.0171
0.0134
0.0163
0.0147
0.0159
0.0159
0.0153
0.0175
0.0161
0.0142
0.0144
0.0159
0.0183
0.0180
0.0178
0.0246
0.0263
0.0234
0.0268
0.0241
0.0242
0.0264
0.0261
0.0280
0.0259
0.0273
0.0210
0.0203
0.0477
0.0561
0.0494
0.0340
0.0294
0.0285
0.0222
0.0264
0.0283
0.0333
0.0302
0.0275
0.0290
0.0268
0.0242
Table 7.1 continued
1994.7975
1994.7590
1994.7205
1994.6820
1994.6436
1994.6051
1994.5666
1994.5281
1994.4897
1994.4512
1994.4127
1994.3742
1994.3358
1994.2973
1994.2588
1994.2203
1994.1819
1994.1434
1994.1049
1994.0664
1994.0280
1993.9895
1993.9510
1993.9125
1993.8741
1993.8356
1993.7971
1993.7586
1993.7202
1993.6817
1993.6432
1993.6048
1993.5663
1993.5278
1993.4893
1993.4509
1993.4124
1993.3739
1993.3354
1993.2970
1993.2585
1993.2200
1993.1815
1993.1431
1993.1046
1993.0661
1993.0276
1992.9892
1992.9507
1992.9122
1992.8737
1992.8353
1992.7968
1.3436
1.3255
1.3074
1.3215
1.3452
1.3690
1.3376
1.3063
0.9540
1.0120
1.4878
1.7975
1.8533
1.9090
1.7773
1.6137
1.5031
1.4876
1.4641
1.4406
1.3241
1.2076
0.7853
0.4667
0.4395
0.4122
0.3835
0.3474
0.3328
0.3536
0.3743
0.4523
0.4845
0.5021
0.6233
0.5694
0.6227
0.6760
0.6722
0.7643
0.7623
0.7602
0.9733
0.9874
1.0014
1.0177
1.2405
1.3020
1.3210
1.3305
1.3400
1.3646
1.3891
4.0258
4.0905
4.0509
4.0736
3.8157
3.5461
3.4412
3.4232
3.4086
3.3764
3.3347
3.3363
3.4109
3.3945
3.3947
3.4470
3.5201
3.4241
3.4579
3.5855
3.5843
3.6150
3.6730
3.5939
3.5600
3.6420
3.6246
3.6188
3.8147
3.7750
3.6878
3.8205
3.7936
3.7299
3.7043
3.7248
3.7080
3.6516
3.6769
3.6810
3.6466
3.5809
3.5669
3.6192
3.5178
3.5083
3.4352
3.5437
3.6969
3.7282
3.5767
3.4780
3.6313
235
0.9520
0.8688
0.7402
0.6225
0.6037
0.6107
0.5916
0.5547
0.5808
0.5903
0.5963
0.6512
0.6384
0.6758
0.6879
0.6723
0.6582
0.6638
0.6561
0.6583
0.6502
0.6482
0.5415
0.5257
0.5406
0.4782
0.4855
0.4566
0.4643
0.4436
0.4389
0.4669
0.4695
0.5130
0.4862
0.5089
0.6191
0.6797
0.6306
0.6937
0.6981
0.7345
0.6186
0.6057
0.6227
0.8193
0.7400
0.7328
0.6945
0.7190
0.6257
0.6850
0.7608
0.0314
0.0398
0.1569
0.0957
0.0575
0.0307
0.0190
0.0205
0.0250
0.0230
0.0198
0.0167
0.0209
0.0245
0.0230
0.0190
0.0242
0.0246
0.0211
0.0210
0.0242
0.0242
0.0227
0.0201
0.0178
0.0195
0.0218
0.0201
0.0194
0.0188
0.0229
0.0232
0.0213
0.0230
0.0246
0.0220
0.0219
0.0233
0.0255
0.0276
0.0291
0.0278
0.0295
0.0508
0.0468
0.0384
0.0376
0.0320
0.0402
0.0384
0.0306
0.0283
0.0345
Table 7.1 continued
1992.7583
1992.7198
1992.6814
1992.6429
1992.6044
1992.5659
1992.5275
1992.4890
1992.4505
1992.4121
1992.3736
1992.3351
1992.2966
1992.2582
1992.2197
1992.1812
1992.1427
1992.1043
1992.0658
1992.0273
1991.9888
1991.9504
1991.9119
1991.8734
1991.8349
1991.7965
1991.7580
1991.7195
1991.6810
1991.6426
1991.6041
1991.5656
1991.5271
1991.4887
1991.4502
1991.4117
1991.3733
1991.3348
1991.2963
1991.2578
1991.2194
1991.1809
1991.1424
1991.1039
1991.0655
1991.0270
1990.9885
1990.9500
1990.9116
1990.8731
1990.8346
1990.7961
1990.7577
1.5268
1.6562
1.3777
1.3751
1.3726
1.3435
1.0327
1.0766
1.4501
1.5582
1.5350
1.6327
1.7304
1.7836
1.7892
1.9418
2.0085
1.9537
1.7304
1.5071
1.3214
1.0039
1.0024
1.0009
1.2585
1.3810
1.3990
1.3687
1.3535
1.3383
1.3258
1.2716
1.3245
1.3781
1.4317
1.3928
1.1714
1.1817
1.1920
1.3480
1.3478
1.3477
1.3630
1.3783
1.3844
1.3905
1.4163
1.3632
1.3102
1.1205
1.2806
1.1229
0.8160
4.0820
3.9540
3.6835
3.7574
3.9510
4.0462
3.7804
3.7396
3.7115
3.6150
3.5401
3.3466
3.2332
3.4327
3.9784
3.8951
3.7914
3.6605
3.6059
3.5758
3.7069
3.8542
3.9221
4.0299
4.0271
4.0013
3.8593
3.7970
3.7297
3.8668
3.7493
3.6800
3.6741
3.7297
3.5613
3.3958
3.3510
3.3973
3.4354
3.3823
3.4489
3.4714
3.5047
3.4978
3.4901
3.5317
3.5584
3.5520
3.5518
3.5652
3.5511
3.6695
3.7627
236
0.7110
0.5703
0.5626
0.5359
0.5016
0.5232
0.4511
0.4306
0.4528
0.4337
0.5360
0.5775
0.5649
0.7487
0.9087
0.8551
0.7975
0.7593
0.7442
0.7344
0.8102
0.9143
0.9286
0.8298
0.7528
0.6929
0.5571
0.4171
0.4093
0.4166
0.4561
0.5163
0.5472
0.5687
0.5518
0.5590
0.6193
0.6468
0.6427
0.6256
0.5842
0.5649
0.5416
0.4959
0.4806
0.4665
0.4902
0.4831
0.4339
0.4082
0.4106
0.3750
0.3280
0.0373
0.0330
0.0329
0.0323
0.0361
0.0348
0.0298
0.0311
0.0263
0.0238
0.0169
0.0241
0.0175
0.0230
0.0272
0.0313
0.0341
0.0262
0.0229
0.0223
0.0614
0.0637
0.0526
0.0442
0.0373
0.0410
0.0413
0.0278
0.0304
0.0251
0.0204
0.0212
0.0220
0.0224
0.0209
0.0202
0.0195
0.0169
0.0143
0.0142
0.0171
0.0164
0.0159
0.0165
0.0163
0.0242
0.0307
0.0240
0.0256
0.0271
0.0299
0.0300
0.0251
Table 7.1 continued
1990.7192
1990.6807
1990.6422
1990.6038
1990.5653
1990.5268
1990.4883
1990.4499
1990.4114
1990.3729
1990.3344
1990.2960
1990.2575
1990.2190
1990.1806
1990.1421
1990.1036
1990.0651
1990.0267
1989.9882
1989.9497
1989.9112
1989.8728
1989.8343
1989.7958
1989.7573
1989.7189
1989.6804
1989.6419
1989.6034
1989.5650
1989.5265
1989.4880
1989.4495
1989.4111
1989.3726
1989.3341
1989.2956
1989.2572
1989.2187
1989.1802
1989.1418
1989.1033
1989.0648
1989.0263
1988.9879
1988.9494
1988.9109
1988.8724
1988.8340
1988.7955
1988.7570
1988.7185
0.8529
0.8898
0.8686
0.8474
0.9165
0.8694
0.8721
0.8747
0.9208
0.9669
0.8029
0.8365
1.0002
0.9906
0.9945
0.9964
0.9983
1.1448
1.3396
1.5345
1.5740
1.6125
1.6129
1.6134
1.7186
1.6049
1.7341
1.7651
1.7961
1.7228
1.6495
1.2805
1.4656
1.3757
1.6608
1.5854
1.6315
1.4778
1.4662
1.4546
1.3765
1.3385
1.2511
1.3276
1.0853
3.1244
3.1643
3.2041
3.3998
3.4195
3.4392
3.7489
3.9523
3.7753
3.8423
3.7638
3.7057
3.7691
3.6895
3.6221
3.5283
3.4881
3.4783
3.5129
3.5826
3.6113
3.6137
3.5823
3.4776
3.5159
3.5111
3.6026
3.6886
3.8242
3.8661
3.9515
4.0223
4.0033
4.0170
4.0158
4.0503
4.1009
4.1729
4.3357
4.0488
3.9611
3.7246
3.6345
3.5340
3.4732
3.4869
3.4729
3.4775
3.4331
3.4933
3.5177
3.4484
3.4423
3.4889
3.5546
3.6367
3.5180
3.5428
3.5797
3.5974
3.6008
237
0.3624
0.3836
0.4358
0.4787
0.5527
0.6030
0.6201
0.6673
0.6691
0.7166
0.7505
0.7509
0.7512
0.7749
0.7439
0.7235
0.7224
0.6338
0.5600
0.4633
0.4546
0.5259
0.6423
0.6502
0.6439
0.6156
0.6415
0.7217
0.8651
0.9296
0.9742
0.7743
0.7897
0.7781
0.9571
0.9734
0.9428
0.8509
0.8279
0.7879
0.7507
0.7650
0.7413
0.6883
0.7454
1.0064
0.9602
1.0257
0.9920
0.6519
0.5378
0.5165
0.4980
0.0202
0.0198
0.0244
0.0212
0.0238
0.0192
0.0216
0.0217
0.0190
0.0175
0.0150
0.0159
0.0176
0.0184
0.0171
0.0177
0.0164
0.0179
0.0180
0.0186
0.0229
0.0222
0.0219
0.0232
0.0227
0.0242
0.0268
0.0307
0.0323
0.0280
0.0408
0.0478
0.0365
0.0258
0.0262
0.0275
0.0220
0.0251
0.0181
0.0141
0.0156
0.0192
0.0207
0.0180
0.0172
0.0169
0.0244
0.0212
0.0220
0.0284
0.0217
0.0233
0.0193
Table 7.1 continued
1988.6801
1988.6416
1988.6031
1988.5646
1988.5262
1988.4877
1988.4492
1988.4107
1988.3723
1988.3338
1988.2953
1988.2568
1988.2184
1988.1799
1988.1414
1988.1029
1988.0645
1988.0260
1987.9875
1987.9491
1987.9106
1987.8721
1987.8336
1987.7952
1987.7567
1987.7182
1987.6797
1987.6413
1987.6028
1987.5643
1987.5258
1987.4874
1987.4489
1987.4104
1987.3719
1987.3335
1987.2950
1987.2565
1987.2180
1987.1796
1987.1411
1987.1026
1987.0641
1987.0257
1986.9872
1986.9487
1986.9102
1986.8718
1986.8333
1986.7948
1986.7564
1986.7179
1986.6794
4.0946
4.2734
4.1730
2.1654
2.1075
2.0496
1.8682
1.9374
1.5711
1.6154
1.4107
1.2806
1.3776
1.5702
1.7171
1.9999
2.1485
2.3731
2.3803
2.3876
2.2804
2.3469
2.5041
2.2655
2.2345
2.2035
1.9031
1.6666
1.4590
1.3485
1.4074
1.4176
1.2988
1.5829
2.0247
3.1021
3.0740
3.2937
3.3107
3.2482
3.0869
3.0030
2.7326
2.2822
1.8298
2.5274
2.5457
2.5641
2.5308
2.6327
3.0961
3.0848
3.0735
3.6588
3.7064
3.7051
3.6780
3.7629
3.8889
3.7792
3.6345
3.5417
3.5258
3.5149
3.4870
3.4509
3.4180
3.4136
3.4591
3.4925
3.6474
3.7680
3.7258
3.6486
3.5905
3.5855
3.6408
3.7057
3.6540
3.6741
3.6652
3.8735
4.4330
3.8690
3.7037
3.8529
3.8348
3.8440
4.1228
3.9933
3.7164
3.7070
3.5754
3.5297
3.5484
3.5509
3.5741
3.6446
3.6861
3.7137
3.7204
3.7051
3.7203
3.6909
3.6756
3.5781
238
0.5195
0.5405
0.5357
0.5534
0.5616
0.7618
0.7674
0.7114
0.7017
0.7507
0.7122
0.6805
0.7239
0.8078
0.8988
0.8917
0.9953
1.1267
1.1150
1.1235
1.0445
0.9836
0.8691
0.8288
0.9806
0.6800
0.5989
0.5580
0.5792
0.8076
0.8420
0.8676
0.9660
0.8587
0.9234
1.0973
1.1019
0.9874
0.8804
0.7303
0.6819
0.6629
0.6345
0.6194
0.6188
0.6279
0.6666
0.6894
0.6896
0.6522
0.5952
0.5977
0.6610
0.0187
0.0275
0.0253
0.0212
0.0285
0.0309
0.0298
0.0308
0.0270
0.0260
0.0212
0.0232
0.0230
0.0227
0.0229
0.0238
0.0248
0.0258
0.0215
0.0188
0.0214
0.0214
0.0234
0.0272
0.0333
0.0332
0.0276
0.0268
0.0288
0.0437
0.0291
0.0216
0.0198
0.0231
0.0347
0.0512
0.0355
0.0203
0.0251
0.0228
0.0196
0.0228
0.0343
0.0357
0.0400
0.0529
0.0656
0.0806
0.0847
0.0892
0.0882
0.0745
0.0571
Table 7.1 continued
1986.6409
1986.6025
1986.5640
1986.5255
1986.4870
1986.4486
1986.4101
1986.3716
1986.3331
1986.2947
1986.2562
1986.2177
1986.1792
1986.1408
1986.1023
1986.0638
1986.0253
1985.9869
1985.9484
1985.9099
1985.8714
1985.8330
1985.7945
1985.7560
1985.7176
1985.6791
1985.6406
1985.6021
1985.5637
1985.5252
1985.4867
1985.4482
1985.4098
1985.3713
1985.3328
1985.2943
1985.2559
1985.2174
1985.1789
1985.1404
1985.1020
1985.0635
1985.0250
1984.9865
1984.9481
1984.9096
1984.8711
1984.8326
1984.7942
1984.7557
1984.7172
1984.6787
1984.6403
3.0773
3.0812
2.9548
2.3881
2.0568
1.7254
1.8576
2.0808
2.0765
1.7369
1.7336
1.7302
1.8923
1.9530
1.9439
1.9347
1.7708
1.4385
1.2254
1.3596
1.7569
1.7453
1.7337
1.5684
1.4524
1.3880
1.4389
1.4456
1.4523
1.3978
1.2982
0.9164
1.4965
1.9317
2.5872
2.7420
2.8967
2.9208
2.8677
2.8148
2.7799
2.7450
2.6330
2.5210
1.9880
2.1194
1.5091
1.4010
1.2928
1.3350
1.4614
1.4441
1.4268
3.3609
3.2028
3.2509
3.3616
3.3749
3.3765
3.3996
3.4387
3.4973
3.5635
3.5813
3.5842
3.5587
3.6313
3.8532
4.0818
4.0765
3.9042
3.7465
3.6046
3.5406
3.5096
3.5064
3.4789
3.4797
3.4471
3.4346
3.4305
3.4056
3.2957
3.2242
3.3019
3.3646
3.4558
3.5966
3.5676
3.5562
3.5995
3.6247
3.6257
3.6522
3.8323
3.9638
3.9832
3.9329
3.8714
3.8478
3.8113
3.7295
3.6381
3.5000
3.3149
3.1933
239
0.7076
0.7475
0.8378
0.9643
1.0232
1.0093
0.9144
0.8266
0.7765
0.7678
0.7870
0.8007
0.7957
0.7793
0.7720
0.8773
1.0020
1.0012
0.9868
0.9681
0.9138
0.9290
1.0238
1.0901
1.1694
1.2101
1.2641
1.3419
1.3098
1.1546
1.0302
0.9516
0.8859
0.8428
0.7741
0.7291
0.7324
0.7228
0.6256
0.5548
0.5757
0.5892
0.5815
0.6152
0.7580
0.8610
0.9182
0.9307
0.9711
0.9790
0.9901
0.9521
0.8907
0.0709
0.0937
0.1007
0.0933
0.0910
0.0799
0.0699
0.0658
0.0592
0.0535
0.0486
0.0407
0.0437
0.0482
0.0484
0.0468
0.0440
0.0603
0.0641
0.0435
0.0356
0.0384
0.0453
0.0481
0.0490
0.0443
0.0422
0.0440
0.0474
0.0521
0.0493
0.0397
0.0348
0.0341
0.0337
0.0381
0.0440
0.0443
0.0390
0.0389
0.0369
0.0301
0.0296
0.0308
0.0332
0.0335
0.0331
0.0318
0.0304
0.0305
0.0289
0.0290
0.0343
Table 7.1 continued
1984.6018
1984.5633
1984.5249
1984.4864
1984.4479
1984.4094
1984.3710
1984.3325
1984.2940
1984.2555
1984.2171
1984.1786
1984.1401
1984.1016
1984.0632
1984.0247
1983.9862
1983.9477
1983.9093
1983.8708
1983.8323
1983.7938
1983.7554
1983.7169
1983.6784
1983.6399
1983.6015
1983.5630
1983.5245
1983.4861
1983.4476
1983.4091
1983.3706
1983.3322
1983.2937
1983.2552
1983.2167
1983.1783
1983.1398
1983.1013
1983.0628
1983.0244
1982.9859
1982.9474
1982.9089
1982.8705
1982.8320
1982.7935
1982.7550
1982.7166
1982.6781
1982.6396
1982.6011
1.3964
1.4476
1.5526
1.0653
1.3014
2.0111
2.1295
2.2479
2.1991
2.3304
2.3622
2.3940
2.4303
2.3570
2.3249
2.2843
2.0343
1.7844
1.4071
1.2289
1.1377
1.0697
0.9941
1.2169
1.1624
0.9806
0.8039
0.8646
0.9254
0.9565
0.9877
1.3088
1.4685
1.4982
1.4190
1.3398
1.6011
1.6100
1.6188
1.6706
1.8347
2.1483
2.2357
2.3231
2.3915
2.7246
2.5728
2.4689
2.3872
2.3055
2.1896
1.9426
1.8473
3.2358
3.2517
3.1884
3.1739
3.1965
3.2654
3.3189
3.3294
3.3077
3.3153
3.2924
3.1425
3.0455
3.2259
3.3877
3.4543
3.4554
3.5201
3.5169
3.4974
3.4534
3.4627
3.4325
3.4100
3.4287
3.4181
3.3274
3.1881
3.3428
3.5266
3.6148
3.7633
3.6462
3.4408
3.4468
3.4748
3.4141
3.4439
3.5515
3.6035
3.7454
3.7459
3.5960
3.5121
3.5433
3.5900
3.6155
3.6208
3.6178
3.6273
3.6042
3.5309
3.5129
240
0.7680
0.7613
0.8277
0.8526
0.8780
0.8916
0.9089
0.9096
0.8925
0.8618
0.8527
0.8493
0.8349
0.7954
0.7515
0.7287
0.7292
0.7902
0.8328
0.8245
0.8441
0.8886
0.9120
0.9415
0.9796
1.0304
1.1885
1.3657
1.4654
1.5741
1.9952
2.6220
2.4016
1.5735
1.2727
1.1695
1.0288
0.9542
0.9205
0.8526
0.8456
0.8986
0.9083
0.8352
0.7931
0.8100
0.8286
0.8439
0.8146
0.7846
0.7859
0.8503
0.9142
0.0367
0.0440
0.0531
0.0577
0.0575
0.0546
0.0527
0.0511
0.0481
0.0454
0.0415
0.0410
0.0409
0.0376
0.0317
0.0268
0.0261
0.0259
0.0261
0.0268
0.0263
0.0263
0.0253
0.0246
0.0251
0.0286
0.0321
0.0354
0.0338
0.0315
0.0331
0.0387
0.0436
0.0386
0.0318
0.0313
0.0310
0.0295
0.0271
0.0255
0.0275
0.0342
0.0372
0.0354
0.0305
0.0274
0.0263
0.0264
0.0266
0.0300
0.0365
0.0411
0.0401
Table 7.1 continued
1982.5627
1982.5242
1982.4857
1982.4472
1982.4088
1982.3703
1982.3318
1982.2934
1982.2549
1982.2164
1982.1779
1982.1395
1982.1010
1982.0625
1982.0240
1981.9856
1981.9471
1981.9086
1981.8701
1981.8317
1981.7932
1981.7547
1981.7162
1981.6778
1981.6393
1981.6008
1981.5623
1981.5239
1981.4854
1981.4469
1981.4084
1981.3700
1981.3315
1981.2930
1981.2546
1981.2161
1981.1776
1981.1391
1981.1007
1981.0622
1981.0237
1980.9852
1980.9468
1980.9083
1980.8698
1980.8313
1980.7929
1980.7544
1980.7159
1980.6774
1980.6390
1980.6005
1980.5620
1.7267
1.6061
1.5688
1.4511
1.5386
1.3998
1.7199
1.8012
1.8824
1.9430
1.9434
1.9439
1.7494
1.6009
1.6562
1.7116
2.1308
2.1712
2.2116
1.9174
1.8347
1.7520
1.7135
1.5708
1.7651
1.7789
1.7927
2.0986
2.1194
2.1402
2.1484
2.3490
2.5162
2.5067
2.4718
2.4368
2.3218
2.5008
2.1762
1.8330
1.8544
2.0948
2.3352
2.6810
2.8247
2.8996
2.8706
2.7182
2.5666
2.4049
2.3642
2.3236
1.6359
3.4651
3.4211
3.4112
3.4136
3.3661
3.3151
3.2616
3.2863
3.2628
3.2057
3.1812
3.1691
3.2514
3.3690
3.5207
3.5723
3.4414
3.3902
3.3671
3.3687
3.5575
3.6768
3.7797
4.0276
4.0635
3.9207
3.8222
3.7329
3.7048
3.5843
3.4514
3.2778
3.1783
3.3034
3.4162
3.4839
3.6734
3.7109
3.4889
3.2713
3.2422
3.3231
3.3456
3.3607
3.3691
3.3266
3.2782
3.2490
3.2439
3.2750
3.4378
3.6736
3.7911
241
0.9727
0.9760
0.9023
0.8374
0.7949
0.7853
0.7689
0.7894
0.8016
0.8231
0.8680
0.9228
1.0219
1.1698
1.3296
1.3860
1.1691
0.8814
0.8025
0.7378
0.6478
0.6350
0.7658
0.9422
0.9383
0.8107
0.6958
0.6704
0.7589
0.7827
0.7511
0.7751
0.8351
0.9781
1.1452
1.2692
1.6179
1.7768
1.5478
1.0990
0.6908
0.5920
0.5786
0.5563
0.5424
0.5095
0.4896
0.4757
0.4825
0.4887
0.5730
0.6551
0.6744
0.0365
0.0592
0.1005
0.0797
0.0379
0.0351
0.0353
0.0363
0.0326
0.0295
0.0253
0.0215
0.0229
0.0256
0.0279
0.0304
0.0385
0.0349
0.0240
0.0263
0.0301
0.0351
0.0378
0.0446
0.0587
0.0686
0.0653
0.0473
0.0374
0.0412
0.0480
0.0538
0.0476
0.0394
0.0421
0.0448
0.0553
0.0733
0.0714
0.0576
0.0460
0.0337
0.0281
0.0265
0.0248
0.0239
0.0233
0.0232
0.0234
0.0252
0.0260
0.0243
0.0218
Table 7.1 continued
1980.5235
1980.4851
1980.4466
1980.4081
1980.3696
1980.3312
1980.2927
1980.2542
1980.2157
1980.1773
1980.1388
1980.1003
1980.0619
1980.0234
1979.9849
1979.9464
1979.9080
1979.8695
1979.8310
1979.7925
1979.7541
1979.7156
1979.6771
1979.6386
1979.6002
1979.5617
1979.5232
1979.4847
1979.4463
1979.4078
1979.3693
1979.3308
1979.2924
1979.2539
1979.2154
1979.1769
1979.1385
1979.1000
1979.0615
1979.0230
1978.9846
1978.9461
1978.9076
1978.8692
1978.8307
1978.7922
1978.7537
1978.7153
1978.6768
1978.6383
1978.5998
1978.5614
1978.5229
1.2818
1.1674
1.1409
1.4013
1.4723
1.5433
1.4203
1.3877
1.4952
1.5201
1.4485
1.4822
1.5158
1.8381
1.8331
1.8819
1.7987
1.7681
1.7320
1.6959
1.6719
1.6733
1.6432
1.4013
1.6969
2.2229
2.3807
2.5384
3.2587
3.5645
5.3442
5.4775
5.5255
5.5718
5.6180
5.4069
5.3381
6.6184
6.1700
5.8080
4.0886
4.0146
3.9407
3.8307
3.5416
3.2534
2.6270
1.1364
1.2545
1.5085
1.7625
2.5469
2.8428
3.7325
3.6340
3.6243
3.5695
3.4528
3.4018
3.4446
3.5640
3.7104
3.7721
3.6853
3.6408
3.6378
3.6683
3.8523
3.9838
4.1130
4.2522
4.4350
4.3921
4.0757
3.9836
3.9833
3.9608
4.1943
4.1886
3.9094
3.7300
3.7171
3.8339
3.9846
4.0832
4.1459
4.2351
4.2746
4.2579
4.2579
4.2579
4.2579
4.2579
4.2550
4.3030
4.3129
4.3129
4.3129
4.3129
4.3129
4.2679
4.1311
3.9082
3.6657
3.5381
3.4565
242
0.6727
0.7563
0.8035
0.9084
0.8431
0.8450
0.8913
0.9563
1.0270
1.0955
1.1902
1.2258
1.1409
1.0697
1.0092
0.9389
0.8304
0.8079
0.7773
0.8029
0.9715
1.1202
1.2370
1.3078
1.3505
1.3340
1.3950
1.6594
1.6793
1.2978
0.9571
0.7946
0.7376
1.0809
2.3266
1.7623
0.9163
0.8449
0.8974
0.9032
0.9364
0.9289
0.9263
0.8758
0.8298
0.7688
0.7515
1.0563
1.3651
1.3726
1.2936
1.3364
1.3465
0.0239
0.0216
0.0188
0.0187
0.0202
0.0216
0.0212
0.0211
0.0220
0.0236
0.0256
0.0256
0.0218
0.0191
0.0203
0.0221
0.0242
0.0243
0.0225
0.0227
0.0254
0.0283
0.0293
0.0286
0.0251
0.0273
0.0272
0.0309
0.0395
0.0384
0.0391
0.0391
0.0360
0.0322
0.0299
0.0314
0.0250
0.0225
0.0270
0.0281
0.0298
0.0349
0.0350
0.0287
0.0225
0.0186
0.0188
0.0204
0.0246
0.0308
0.0295
0.0310
0.0350
Table 7.1 continued
1978.4844
1978.4459
1978.4075
1978.3690
1978.3305
1978.2920
1978.2536
1978.2151
1978.1766
1978.1381
1978.0997
1978.0612
1978.0227
1977.9842
1977.9458
1977.9073
1977.8688
1977.8304
1977.7919
1977.7534
1977.7149
1977.6765
1977.6380
1977.5995
1977.5610
1977.5226
1977.4841
1977.4456
1977.4071
1977.3687
1977.3302
1977.2917
1977.2532
1977.2148
1977.1763
1977.1378
1977.0993
1977.0609
1977.0224
1976.9839
1976.9454
1976.9070
1976.8685
1976.8300
1976.7915
1976.7531
1976.7146
1976.6761
1976.6377
1976.5992
1976.5607
1976.5222
1976.4838
2.7917
2.8383
2.8717
2.8742
2.8768
2.8855
2.6958
2.6311
1.9539
1.7795
2.2462
2.3242
2.4023
2.5845
2.5663
2.5482
2.3998
2.3107
1.9399
2.0445
2.1490
2.8394
2.7399
3.1450
2.9829
3.6744
3.7893
3.9043
3.9236
3.9113
3.5495
2.7303
2.6664
2.6025
1.9679
1.9288
1.1228
0.8869
0.7878
0.7272
0.6666
0.6811
0.7011
0.5308
0.6415
0.6397
0.6963
0.7530
1.0427
1.2391
1.4160
1.4203
1.4396
3.5968
3.8107
3.8896
3.8659
4.0851
4.1381
3.9154
3.9210
4.0257
3.9987
3.9941
4.0881
4.2494
4.4021
4.5047
4.4992
4.4195
4.3679
4.3430
4.2642
4.0139
3.6640
3.5449
3.4252
3.3945
3.4075
3.4356
3.4522
3.4860
3.5346
3.5846
3.6494
3.7124
3.7493
3.7966
3.9102
3.9515
3.8005
3.9036
4.0107
4.1547
4.2513
4.2795
4.3670
4.4479
4.4754
4.4042
4.3520
4.2922
4.3338
4.2876
3.9321
3.6846
243
1.1005
0.8991
0.8124
0.8979
0.8969
0.8218
0.8884
1.1131
1.3743
1.4443
1.6677
1.6956
1.2855
0.9750
0.8887
0.8817
0.8769
0.8751
0.8757
0.8433
0.8155
0.7443
0.7344
0.7314
0.7042
0.6845
0.6687
0.6622
0.6557
0.6570
0.6550
0.6373
0.6322
0.6462
0.6773
0.7214
0.7703
0.8864
1.0473
1.1366
1.1761
1.1940
1.2472
1.3360
1.4084
1.4543
1.4275
1.2222
0.9902
0.8356
0.7549
0.7278
0.7570
0.0356
0.0304
0.0263
0.0234
0.0249
0.0241
0.0275
0.0316
0.0347
0.0334
0.0296
0.0304
0.0257
0.0237
0.0209
0.0190
0.0179
0.0173
0.0172
0.0174
0.0194
0.0202
0.0199
0.0229
0.0238
0.0244
0.0264
0.0263
0.0271
0.0253
0.0248
0.0232
0.0217
0.0213
0.0216
0.0216
0.0243
0.0263
0.0309
0.0322
0.0302
0.0285
0.0263
0.0262
0.0280
0.0290
0.0303
0.0343
0.0303
0.0300
0.0278
0.0299
0.0351
Table 7.1 continued
1976.4453
1976.4068
1976.3683
1976.3299
1976.2914
1976.2529
1976.2144
1976.1760
1976.1375
1976.0990
1976.0605
1976.0221
1975.9836
1975.9451
1975.9066
1975.8682
1975.8297
1975.7912
1975.7527
1975.7143
1975.6758
1975.6373
1975.5989
1975.5604
1975.5219
1975.4834
1975.4450
1975.4065
1975.3680
1975.3295
1975.2911
1975.2526
1975.2141
1975.1756
1975.1372
1975.0987
1975.0602
1975.0217
1974.9833
1974.9448
1974.9063
1974.8678
1974.8294
1974.7909
1974.7524
1974.7139
1974.6755
1974.6370
1974.5985
1974.5600
1974.5216
1974.4831
1974.4446
1.4590
1.4002
1.3681
1.3174
1.3783
1.5342
1.4937
1.4532
1.3305
1.4638
1.4977
1.5599
1.5865
1.6900
1.7936
2.5917
2.4189
2.4717
2.5245
2.7204
2.6899
3.1734
3.6568
3.5869
3.5749
3.3281
2.8359
2.3436
2.0982
1.9143
1.7777
1.6842
0.6283
0.6352
0.6302
0.6253
0.6566
0.8401
0.9270
0.9856
1.0855
1.1853
1.9054
2.9139
3.5097
3.7425
4.0353
4.0156
3.9958
3.8870
3.7653
3.5134
2.6302
3.6529
3.6437
3.7919
3.9088
3.9625
4.0006
3.9922
4.0261
4.1195
4.1983
4.2612
4.1968
4.2190
4.4418
4.5879
4.5690
4.3833
4.1628
3.9831
3.8664
3.8103
3.8001
3.7152
3.6090
3.5333
3.5502
3.5962
3.6203
3.6623
3.6625
3.6654
3.6619
3.7039
3.7089
3.7188
3.7565
3.8254
3.8925
3.9156
3.9379
3.9434
3.9435
3.9237
3.8965
3.8799
3.8882
3.9794
4.0644
4.1024
4.0841
4.0890
4.0618
3.9764
244
1.0485
1.2088
1.1799
1.2015
1.2978
1.4990
1.7342
2.0282
2.3273
2.3545
1.7060
1.1534
1.1444
1.2617
1.3281
1.2993
1.2066
1.0973
1.0418
1.0256
1.0371
1.0505
1.0009
0.8792
0.7747
0.7770
0.8435
0.8876
0.8831
0.8939
0.9713
1.1226
1.3517
1.5505
1.6142
1.4747
1.2540
1.0243
0.9232
0.8795
0.8872
0.8674
0.7875
0.7098
0.6746
0.6718
0.7015
0.7565
0.7955
0.8216
0.8302
0.8473
0.8435
0.0305
0.0275
0.0305
0.0333
0.0322
0.0337
0.0335
0.0338
0.0340
0.0364
0.0360
0.0339
0.0307
0.0281
0.0249
0.0227
0.0222
0.0214
0.0209
0.0222
0.0239
0.0257
0.0267
0.0266
0.0291
0.0317
0.0350
0.0381
0.0398
0.0411
0.0377
0.0354
0.0337
0.0377
0.0412
0.0400
0.0333
0.0266
0.0242
0.0245
0.0239
0.0218
0.0201
0.0193
0.0187
0.0186
0.0201
0.0209
0.0195
0.0181
0.0174
0.0156
0.0147
Table 7.1 continued
1974.4062
1974.3677
1974.3292
1974.2907
1974.2523
1974.2138
1974.1753
1974.1368
1974.0984
1974.0599
1974.0214
1973.9829
1973.9445
1973.9060
1973.8675
1973.8290
1973.7906
1973.7521
1973.7136
1973.6751
1973.6367
1973.5982
1973.5597
1973.5212
1973.4828
1973.4443
1973.4058
1973.3673
1973.3289
1973.2904
1973.2519
1973.2135
1973.1750
1973.1365
1973.0980
1973.0596
1973.0211
1972.9826
1972.9441
1972.9057
1972.8672
1972.8287
1972.7902
1972.7518
1972.7133
1972.6748
1972.6363
1972.5979
1972.5594
1972.5209
1972.4824
1972.4440
1972.4055
1.3340
1.2485
1.1629
0.8911
0.6019
0.5097
0.6689
0.7701
0.8561
0.9421
1.0534
1.0611
1.1652
1.2999
1.5402
1.8031
2.0661
2.1187
2.3668
2.5103
2.6089
2.6044
2.5870
2.5695
2.4886
2.2217
1.6678
1.7053
1.3622
1.1340
1.0787
1.0234
1.0458
1.0930
1.0977
1.4103
1.4974
1.5936
1.6975
1.8013
2.2438
2.2736
2.3560
2.3581
2.3602
2.2881
1.9922
1.9693
1.6664
1.5854
1.5044
1.0940
1.0311
3.8967
3.8618
3.8010
3.7424
3.7174
3.6834
3.6817
3.7545
3.7748
3.7635
3.7912
3.8224
3.8201
3.7908
3.8083
3.9131
3.9642
3.9727
3.9807
4.0442
4.0561
4.0212
3.9968
4.0128
4.0679
4.1194
4.1069
4.0679
4.0314
3.9556
3.8633
3.8012
3.8062
3.8274
3.8026
3.7856
3.8351
3.9449
3.9790
3.9662
3.9749
4.0338
4.0592
4.0207
3.9940
4.1040
4.1060
4.0234
3.8419
3.6428
3.5241
3.3732
3.4549
245
0.7770
0.7367
0.7999
0.8518
0.7654
0.6389
0.5214
0.4630
0.4421
0.4730
0.4983
0.5581
0.6223
0.6412
0.6891
0.7113
0.7442
0.7800
0.8667
0.9504
0.9718
0.9463
0.9191
0.9212
0.9464
0.9898
0.9908
0.9335
0.8558
0.8042
0.7924
0.7818
0.7672
0.7285
0.7159
0.6968
0.6785
0.6418
0.6240
0.6032
0.5903
0.5932
0.5928
0.5842
0.5687
0.6254
0.6875
0.7223
0.8072
0.8040
0.6453
0.7025
0.8528
0.0143
0.0161
0.0161
0.0172
0.0185
0.0183
0.0187
0.0190
0.0180
0.0180
0.0200
0.0217
0.0231
0.0232
0.0222
0.0213
0.0220
0.0226
0.0243
0.0254
0.0248
0.0227
0.0214
0.0206
0.0200
0.0205
0.0203
0.0203
0.0189
0.0186
0.0177
0.0179
0.0181
0.0198
0.0207
0.0212
0.0268
0.0465
0.0688
0.0727
0.0728
0.0748
0.0862
0.0940
0.0843
0.0676
0.0670
0.0563
0.0391
0.0232
0.0177
0.0154
0.0143
Table 7.1 continued
1972.3670
1972.3285
1972.2901
1972.2516
1972.2131
1972.1747
1972.1362
1972.0977
1972.0592
1972.0208
1971.9823
1971.9438
1971.9053
1971.8669
1971.8284
1971.7899
1971.7514
1971.7130
1971.6745
1971.6360
1971.5975
1971.5591
1971.5206
1971.4821
1971.4436
1971.4052
1971.3667
1971.3282
1971.2897
1971.2513
1971.2128
1971.1743
1971.1358
1971.0974
1971.0589
1971.0204
1970.9820
1970.9435
1970.9050
1970.8665
1970.8281
1970.7896
1970.7511
1970.7126
1970.6742
1970.6357
1970.5972
1970.5587
1970.5203
1970.4818
1970.4433
1970.4048
1970.3664
0.9694
0.9049
0.8981
0.9644
0.9477
0.9724
0.9970
1.0235
1.0052
1.0685
1.0583
1.0410
1.0237
1.1145
1.1638
1.1301
1.0666
1.0439
1.0294
1.0149
1.0856
1.0835
1.1104
1.0835
0.9790
1.0438
1.1120
1.1802
1.3637
1.4246
1.6589
2.0544
2.6206
2.8457
3.4367
4.0278
4.1362
4.2144
4.0513
4.0369
3.6762
3.6165
3.4532
3.2900
3.1113
2.2623
2.1051
1.8811
1.8500
1.8189
1.7494
1.7314
1.7135
3.5936
3.6689
3.6698
3.7556
3.8750
3.9488
4.0017
4.0919
4.1349
4.0749
4.0271
3.9035
3.9459
3.8933
3.8149
3.7952
3.7756
3.7355
3.7514
3.7442
3.7636
3.7860
3.8013
3.8410
3.8652
3.8477
3.7944
3.8402
3.8881
3.8958
3.8103
3.7654
3.7880
3.9934
4.4126
4.6030
4.4766
4.3897
4.3898
4.3658
4.3165
4.2989
4.1733
4.0113
4.0813
4.0703
4.1318
4.1695
4.1402
4.0067
3.9277
3.8691
3.7535
246
0.8360
0.8084
0.8318
0.7023
0.5655
0.4870
0.4711
0.6143
0.7634
0.8703
1.0435
1.0495
0.8560
0.9995
1.3404
1.4922
1.4508
1.2808
1.1769
1.1206
1.1126
1.1550
1.1565
1.1561
1.1292
1.1059
1.0758
1.0391
0.9942
0.9656
0.9633
0.9604
0.9268
0.8695
0.9485
1.2311
1.1678
1.1185
1.1522
1.1948
1.2165
1.2785
1.2272
1.1359
1.1727
1.2073
1.3122
1.3669
1.4118
1.3154
1.1437
0.9625
0.8716
0.0154
0.0175
0.0168
0.0164
0.0170
0.0172
0.0272
0.0261
0.0276
0.0241
0.0214
0.0237
0.0275
0.0330
0.0363
0.0347
0.0360
0.0381
0.0409
0.0420
0.0455
0.0510
0.0509
0.0498
0.0455
0.0436
0.0429
0.0447
0.0442
0.0453
0.0463
0.0441
0.0440
0.0447
0.0533
0.0714
0.0760
0.0749
0.0786
0.0923
0.1012
0.0986
0.0915
0.0827
0.0651
0.0769
0.0779
0.0675
0.0611
0.0612
0.0546
0.0467
0.0419
Table 7.1 continued
1970.3279
1970.2894
1970.2509
1970.2125
1970.1740
1970.1355
1970.0970
1970.0586
1970.0201
1969.9816
1969.9432
1969.9047
1969.8662
1969.8277
1969.7893
1969.7508
1969.7123
1969.6738
1969.6354
1969.5969
1969.5584
1969.5199
1969.4815
1969.4430
1969.4045
1969.3660
1969.3276
1969.2891
1969.2506
1969.2121
1969.1737
1969.1352
1969.0967
1969.0582
1969.0198
1968.9813
1968.9428
1968.9043
1968.8659
1968.8274
1968.7889
1968.7505
1968.7120
1968.6735
1968.6350
1968.5966
1968.5581
1968.5196
1968.4811
1968.4427
1968.4042
1968.3657
1968.3272
1.5218
1.4008
1.6347
1.7530
1.8311
1.9047
1.9782
2.0786
2.4467
2.5292
2.6815
2.9643
2.9186
2.7878
2.6569
2.7987
3.7287
3.7468
3.5906
3.4344
3.2819
3.1480
2.7919
2.8356
2.8108
2.7860
2.7872
2.3029
1.8186
1.9325
1.8466
1.8395
1.6475
1.6126
1.4699
1.3273
1.2608
1.1914
1.2165
1.2814
1.3693
1.3691
1.3690
1.3284
1.3017
1.2433
1.1101
0.9749
0.8381
0.7187
0.5992
0.5445
0.5826
3.7413
3.8633
3.9898
4.0436
4.0669
4.0825
4.1521
4.2893
4.3684
4.3033
4.2067
4.2411
4.2630
4.2323
4.1293
4.0387
3.9433
3.8871
3.8953
3.8814
3.8378
3.8244
3.8999
4.0537
4.1371
4.2244
4.1991
4.1077
3.9480
3.8502
3.7881
3.7858
3.8268
3.8713
3.8875
3.9461
3.9544
3.9318
3.8980
3.8506
3.8347
3.7898
3.6990
3.6487
3.5320
3.5890
3.5358
3.4915
3.3970
3.3438
3.3634
3.3371
3.3061
247
0.7772
0.7309
0.7186
0.6932
0.6829
0.7192
0.7863
0.8445
0.8296
0.7620
0.6951
0.6763
0.7035
0.7400
0.7447
0.7848
0.8417
0.9016
0.8908
0.8788
0.8982
0.9498
1.0395
1.1254
1.1767
1.2072
1.2018
1.1368
0.9845
0.8230
0.7413
0.7146
0.6893
0.6655
0.6363
0.6393
0.6261
0.6211
0.5893
0.5452
0.4875
0.4889
0.4775
0.5359
0.5554
0.5307
0.5338
0.6166
0.6421
0.7111
0.7500
0.7557
0.7127
0.0395
0.0354
0.0428
0.0437
0.0409
0.0411
0.0416
0.0442
0.0508
0.0595
0.0606
0.0577
0.0536
0.0539
0.0518
0.0550
0.0593
0.0613
0.0563
0.0551
0.0555
0.0569
0.0573
0.0599
0.0605
0.0642
0.0680
0.0706
0.0654
0.0603
0.0617
0.0627
0.0612
0.0575
0.0529
0.0462
0.0391
0.0356
0.0343
0.0348
0.0339
0.0328
0.0300
0.0323
0.0219
0.0161
0.0214
0.0268
0.0257
0.0173
0.0125
0.0111
0.0106
Table 7.1 continued
1968.2888
1968.2503
1968.2118
1968.1733
1968.1349
1968.0964
1968.0579
1968.0194
1967.9810
1967.9425
1967.9040
1967.8655
1967.8271
1967.7886
1967.7501
1967.7116
1967.6732
1967.6347
1967.5962
1967.5578
1967.5193
1967.4808
1967.4423
1967.4039
1967.3654
1967.3269
1967.2884
1967.2500
1967.2115
1967.1730
1967.1345
1967.0961
1967.0576
1967.0191
1966.9806
1966.9422
1966.9037
1966.8652
1966.8267
1966.7883
1966.7498
1966.7113
1966.6728
1966.6344
1966.5959
1966.5574
1966.5190
1966.4805
1966.4420
1966.4035
1966.3651
1966.3266
1966.2881
0.8109
0.9414
1.0369
1.0607
1.0846
1.1420
1.1769
1.2022
1.2397
1.2274
0.9910
0.9383
0.8856
0.8377
0.7528
0.7227
0.6706
0.6843
0.6980
0.6989
0.6998
0.7688
0.9524
1.1358
1.2593
1.4234
1.4924
1.5614
1.6599
1.7678
1.7951
1.7740
1.7530
1.7173
1.6816
1.5526
1.4827
1.4444
1.4062
1.3567
1.3318
1.3037
1.2757
1.2594
1.2427
1.1406
1.1691
1.1774
1.1857
1.4533
1.8867
1.9388
1.9910
3.3632
3.4451
3.5380
3.6270
3.6082
3.5634
3.5788
3.5512
3.5837
3.6167
3.6286
3.6959
3.7397
3.7461
3.7658
3.7842
3.7569
3.6597
3.5383
3.4028
3.4175
3.3356
3.2560
3.2683
3.3224
3.3419
3.3595
3.4107
3.4421
3.4655
3.4653
3.4688
3.4823
3.5871
3.6054
3.6599
3.7422
3.7480
3.7500
3.7832
3.7881
3.7975
3.7692
3.7854
3.7206
3.6017
3.5564
3.5666
3.5316
3.5274
3.5363
3.5369
3.5045
248
0.6685
0.6343
0.6982
0.7785
0.5786
0.4476
0.4681
0.4647
0.4078
0.3719
0.3517
0.3495
0.3715
0.3957
0.4368
0.4850
0.5169
0.5501
0.5658
0.5742
0.5690
0.5809
0.5941
0.5856
0.5887
0.5791
0.5457
0.5126
0.4950
0.4809
0.4785
0.4670
0.4633
0.4630
0.4404
0.4430
0.4894
0.5332
0.5204
0.4939
0.5093
0.5285
0.5486
0.5323
0.4922
0.5208
0.5415
0.5927
0.5392
0.5071
0.5058
0.5079
0.5193
0.0107
0.0109
0.0106
0.0120
0.0109
0.0113
0.0128
0.0136
0.0128
0.0129
0.0122
0.0132
0.0137
0.0140
0.0150
0.0156
0.0153
0.0144
0.0146
0.0143
0.0128
0.0123
0.0140
0.0163
0.0177
0.0156
0.0149
0.0145
0.0165
0.0185
0.0202
0.0204
0.0229
0.0192
0.0197
0.0236
0.0258
0.0274
0.0269
0.0287
0.0298
0.0298
0.0293
0.0327
0.0355
0.0326
0.0312
0.0323
0.0315
0.0288
0.0295
0.0310
0.0302
Table 7.1 continued
1966.2496
1966.2112
1966.1727
1966.1342
1966.0957
1966.0573
1966.0188
1965.9803
1965.9418
1965.9034
1965.8649
1965.8264
1965.7879
1965.7495
1965.7110
1965.6725
1965.6340
1965.5956
1965.5571
1965.5186
1965.4801
1965.4417
1965.4032
1965.3647
1965.3263
1965.2878
1965.2493
1965.2108
1965.1724
1965.1339
1965.0954
1965.0569
1965.0185
1964.9800
1964.9415
1964.9030
1964.8646
1964.8261
1964.7876
1964.7491
1964.7107
1964.6722
1964.6337
1964.5952
1964.5568
1964.5183
1964.4798
1964.4413
1964.4029
1964.3644
1964.3259
1964.2875
1964.2490
2.2333
2.2593
2.2852
2.3688
2.4747
2.5369
2.5991
2.6692
2.7394
2.5734
2.1960
2.1238
2.0515
2.1761
2.4412
2.2931
2.2634
2.2338
2.0468
1.9334
1.8199
1.6792
1.5429
1.5323
1.5217
1.1231
0.9841
0.8452
0.9027
1.0237
1.2214
1.3945
1.5072
1.5592
1.5357
1.5121
1.6402
1.6327
1.6252
1.5952
1.4447
1.2406
1.2165
1.1924
1.1110
1.0321
0.9572
0.8895
0.8217
0.7941
0.8438
0.8512
0.8586
3.5423
3.5696
3.5854
3.5890
3.6588
3.7339
3.7453
3.9088
3.8859
3.8086
3.7703
3.7684
3.7555
3.7570
3.6250
3.5633
3.6147
3.5751
3.5552
3.5559
3.6058
3.5808
3.4868
3.5042
3.4497
3.4181
3.4472
3.5109
3.5977
3.6002
3.4923
3.5065
3.6620
3.6984
3.6520
3.6144
3.6016
3.5665
3.5282
3.4857
3.4812
3.4735
3.4529
3.4677
3.6467
3.6182
3.6210
3.6022
3.5001
3.4747
3.4118
3.3395
3.2597
249
0.5356
0.5269
0.5055
0.4979
0.5281
0.6198
0.9045
1.3452
1.7758
1.9228
1.0784
0.7605
0.8076
0.8361
0.8295
0.7910
0.7675
0.8139
0.8450
0.8541
0.9084
0.9135
0.7894
0.7671
0.7272
0.6354
0.6525
0.6170
0.6207
0.5065
0.3458
0.3660
0.4676
0.4880
0.5309
0.5940
0.5879
0.6241
0.7100
0.7854
0.7969
0.6612
0.5339
0.5366
0.5792
0.5583
0.5372
0.5614
0.5241
0.5306
0.6127
0.6355
0.6610
0.0300
0.0307
0.0316
0.0322
0.0318
0.0343
0.0360
0.0326
0.0297
0.0250
0.0238
0.0239
0.0225
0.0212
0.0214
0.0224
0.0204
0.0200
0.0197
0.0186
0.0221
0.0229
0.0216
0.0225
0.0225
0.0204
0.0221
0.0188
0.0181
0.0275
0.1078
0.0134
0.0135
0.0141
0.0146
0.0183
0.0190
0.0173
0.0162
0.0179
0.0205
0.0176
0.0139
0.0147
0.0173
0.0188
0.0257
0.0220
0.0183
0.0207
0.0183
0.0157
0.0188
Table 7.1 continued
1964.2105
1964.1720
1964.1336
1964.0951
1964.0566
1964.0181
1963.9797
1963.9412
1963.9027
1963.8642
1963.8258
1963.7873
1963.7488
1963.7103
1963.6719
1963.6334
1963.5949
1963.5564
1963.5180
1963.4795
1963.4410
1963.4025
1963.3641
1963.3256
1963.2871
1963.2486
1963.2102
1963.1717
1963.1332
1963.0948
1963.0563
1963.0178
1962.9793
1962.9409
1962.9024
1962.8639
1962.8254
1962.7870
1962.7485
1962.7100
1962.6715
1962.6331
1962.5946
1962.5561
1962.5176
1962.4792
1962.4407
1962.4022
1962.3637
1962.3253
1962.2868
1962.2483
1962.2098
0.9995
0.9871
0.9917
0.9963
1.0284
1.1488
1.3158
1.3567
1.5038
1.6304
1.6245
1.6185
1.7047
1.8369
1.9691
2.0897
2.4453
2.4427
2.4401
2.3961
2.3520
2.1733
2.1687
2.1641
2.0625
2.0357
2.0089
1.8739
1.7389
1.6607
1.3069
1.5827
1.7456
1.8614
1.9852
1.9981
2.0110
2.0253
2.0395
2.2166
2.7136
2.8939
2.6487
2.7768
2.9048
2.9666
2.7136
2.6353
2.5809
2.5265
2.4230
2.3195
2.0259
3.2243
3.2553
3.2445
3.3579
3.4415
3.6531
3.6995
3.7060
3.6540
3.5388
3.4931
3.4971
3.5376
3.4884
3.4694
3.5054
3.5033
3.4791
3.4767
3.4972
3.5257
3.5032
3.5557
3.5609
3.5654
3.5570
3.5635
3.5870
3.6755
3.6486
3.8004
3.7616
3.5699
3.5735
3.6200
3.6129
3.5872
3.6008
3.4949
3.4662
3.4740
3.6416
3.8624
4.0039
3.9297
3.7961
3.6949
3.5887
3.4501
3.3422
3.3153
3.2351
3.2433
250
0.7117
0.8166
1.0435
0.9327
1.0622
1.2187
1.2411
1.5752
1.8062
1.6116
1.1856
0.9662
0.8563
0.7955
0.6929
0.6049
0.5346
0.5574
0.5483
0.5439
0.5357
0.5880
0.6549
0.6973
0.7618
0.7975
0.9292
1.3828
1.4697
1.3424
1.3265
1.6135
1.5110
1.2712
1.1225
0.9731
0.8778
0.7547
0.6588
0.6093
0.5797
0.5348
0.5889
0.6014
0.5966
0.6088
0.6420
0.6907
0.7230
0.7848
0.8442
0.7864
0.7046
0.0207
0.0181
0.0315
0.0364
0.0337
0.0391
0.0345
0.0447
0.0478
0.0436
0.0389
0.0411
0.0422
0.0399
0.0334
0.0354
0.0439
0.0450
0.0691
0.0615
0.0526
0.0467
0.0476
0.0446
0.0447
0.0485
0.0560
0.0536
0.0540
0.0634
0.0638
0.0774
0.0867
0.0773
0.0733
0.0641
0.0573
0.0526
0.0526
0.0558
0.0581
0.0569
0.0623
0.0602
0.0650
0.0600
0.0640
0.0727
0.0727
0.0721
0.0685
0.0703
0.0677
Table 7.1 continued
1962.1714
1962.1329
1962.0944
1962.0559
1962.0175
1961.9790
1961.9405
1961.9021
1961.8636
1961.8251
1961.7866
1961.7482
1961.7097
1961.6712
1961.6327
1961.5943
1961.5558
1961.5173
1961.4788
1961.4404
1961.4019
1961.3634
1961.3249
1961.2865
1961.2480
1961.2095
1961.1710
1961.1326
1961.0941
1961.0556
1961.0171
1960.9787
1960.9402
1960.9017
1960.8633
1960.8248
1960.7863
1960.7478
1960.7094
1960.6709
1960.6324
1960.5939
1960.5555
1960.5170
1960.4785
1960.4400
1960.4016
1960.3631
1960.3246
1960.2861
1960.2477
1960.2092
1960.1707
1.8675
2.3216
2.1290
2.0390
2.2044
2.3698
2.5118
2.5206
2.5386
2.5566
2.4198
2.3652
2.0849
1.8046
1.6144
1.5508
1.2918
1.2668
1.2418
1.1984
1.1984
1.1984
1.1984
1.1984
1.1984
---------------------------------------------------------
3.2433
3.2157
3.1027
3.1282
3.1800
3.2675
3.3404
3.3876
3.3844
3.3609
3.3447
3.3159
3.3178
3.4672
3.7231
3.8597
3.7537
3.7191
3.8112
3.7406
3.7195
3.5429
3.4864
3.3790
3.3359
3.2585
3.3096
3.3423
3.4730
3.3509
3.3057
3.2545
3.2073
3.2207
3.2845
3.3312
3.2808
3.2099
3.3990
3.4138
3.5126
3.4394
3.4705
3.5933
3.5887
3.5180
3.5212
3.5350
3.5802
3.5669
3.4589
3.3402
3.3445
251
0.6085
0.6329
0.6326
0.6488
0.6294
0.6127
0.6544
0.7048
0.7285
0.7521
0.7445
0.6711
0.6176
0.6826
0.6754
0.6318
0.7228
0.8650
1.1542
1.0602
1.1064
0.9889
0.7957
0.7397
0.6832
0.6893
0.7998
0.8258
0.9453
0.9579
0.8981
0.7556
0.6018
0.5700
0.5645
0.5828
0.6185
0.5968
0.5375
0.5959
0.5602
0.5928
0.5024
0.4877
0.5211
0.5565
0.5609
0.5515
0.5629
0.7005
0.7863
0.6941
0.6560
0.0513
0.0696
0.0653
0.0494
0.0482
0.0451
0.0425
0.0420
0.0464
0.0503
0.0494
0.0446
0.0491
0.0548
0.0539
0.0632
0.0627
0.0620
0.0611
0.0711
0.0840
0.0718
0.0522
0.0465
0.0540
0.0411
0.0402
0.0329
0.0577
0.0507
0.0485
0.0378
0.0364
0.0381
0.0399
0.0478
0.0578
0.0494
0.0512
0.0608
0.0414
0.0572
0.0635
0.0441
0.0366
0.0370
0.0369
0.0373
0.0351
0.0398
0.0437
0.0381
0.0260
Table 7.1 continued
1960.1322
1960.0938
1960.0553
1960.0168
1959.9783
1959.9399
1959.9014
1959.8629
1959.8244
1959.7860
1959.7475
1959.7090
1959.6706
1959.6321
1959.5936
1959.5551
1959.5167
1959.4782
1959.4397
1959.4012
1959.3628
1959.3243
1959.2858
1959.2473
1959.2089
1959.1704
1959.1319
1959.0934
1959.0550
1959.0165
1958.9780
1958.9395
1958.9011
1958.8626
1958.8241
1958.7856
1958.7472
1958.7087
1958.6702
1958.6318
1958.5933
1958.5548
1958.5163
1958.4779
1958.4394
1958.4009
1958.3624
1958.3240
1958.2855
1958.2470
1958.2085
1958.1701
1958.1316
-----------------------------------------------------------------------------------------------------------
3.3951
3.2842
3.1531
3.1472
3.5254
3.6064
3.7064
3.4952
3.2865
3.1941
3.1294
3.1518
3.1227
3.0763
3.1292
3.2227
3.2306
3.3007
3.2807
3.2990
3.3254
3.3961
3.3173
3.3713
3.3000
3.3629
3.3933
3.4433
3.2506
3.3043
3.2941
3.2198
3.3171
3.3591
3.3086
3.2248
3.1692
3.2446
3.5804
3.7847
3.5174
3.6068
3.4545
3.4197
3.3968
3.4074
3.3683
3.3378
3.3101
3.2462
3.2927
3.3268
3.2655
252
0.6706
0.7367
0.9333
0.9835
1.0395
1.1379
1.2872
1.6347
1.4574
1.0437
0.7556
0.6672
0.6302
0.5877
0.5652
0.5578
0.4176
0.3678
0.4841
0.5473
0.4951
0.4625
0.5426
0.5627
0.6364
0.5961
0.6101
0.7645
0.7422
0.6600
0.7509
0.7729
0.7471
0.7845
0.8276
0.8167
0.7636
0.6867
0.5698
0.4989
1.1840
0.5705
0.5431
0.4728
0.4981
0.5407
0.5671
0.5223
0.5255
0.5195
0.5050
0.5299
0.5573
0.0264
0.0319
0.0384
0.0437
0.0444
0.0370
0.0456
0.0439
0.0321
0.0305
0.0298
0.0289
0.0275
0.0260
0.0275
0.0273
0.0220
0.0201
0.0173
0.0238
0.0315
0.0237
0.0239
0.0173
0.0184
0.0201
0.0248
0.0288
0.0311
0.0234
0.0203
0.0197
0.0247
0.0290
0.0309
0.0254
0.0182
0.0190
0.0274
0.0256
0.0284
0.0307
0.0269
0.0240
0.0304
0.0302
0.0236
0.0206
0.0221
0.0228
0.0222
0.0239
0.0269
Table 7.1 continued
1958.0931
1958.0546
1958.0162
1957.9777
1957.9392
1957.9007
1957.8623
1957.8238
1957.7853
1957.7468
1957.7084
1957.6699
1957.6314
1957.5929
1957.5545
1957.5160
1957.4775
1957.4391
1957.4006
1957.3621
1957.3236
1957.2852
1957.2467
1957.2082
1957.1697
1957.1313
1957.0928
1957.0543
1957.0158
1956.9774
1956.9389
1956.9004
1956.8619
1956.8235
1956.7850
1956.7465
1956.7080
1956.6696
1956.6311
1956.5926
1956.5541
1956.5157
1956.4772
1956.4387
1956.4003
1956.3618
1956.3233
1956.2848
1956.2464
1956.2079
1956.1694
1956.1309
1956.0925
-----------------------------------------------------------------------------------------------------------
3.1821
3.1858
3.1694
3.1292
3.0624
2.9241
2.9741
3.1259
3.1610
3.1758
3.1510
3.0736
3.0346
3.0430
3.0753
3.1318
3.1690
3.1567
3.1354
3.1583
3.2302
3.2710
3.2481
3.2665
3.2812
3.2937
3.2756
3.3414
3.3730
3.3990
3.3770
3.3847
3.3498
3.3131
3.2968
3.3197
3.3255
3.3251
3.2853
3.3794
3.4534
3.5336
3.6068
3.7110
3.7499
3.8412
3.7876
3.7443
3.7013
3.7216
3.7032
3.6681
3.5158
253
0.5610
0.5522
0.5597
0.5301
0.5375
0.5340
0.5219
0.6332
0.6948
0.6887
0.6097
0.5847
0.5651
0.5367
0.5463
0.5544
0.5713
0.5593
0.5605
0.5621
0.5268
0.3842
0.3696
0.3916
0.3555
0.3326
0.3175
0.3198
0.3206
0.3328
0.3447
0.3410
0.3635
0.4239
0.5497
0.5854
0.5888
0.6246
0.5421
0.5289
0.4922
0.5331
0.4369
0.4107
0.4519
0.5147
0.5132
0.5051
0.5693
0.6132
0.5717
0.5664
0.5625
0.0218
0.0196
0.0147
0.0143
0.0167
0.0149
0.0129
0.0138
0.0166
0.0171
0.0188
0.0166
0.0158
0.0169
0.0181
0.0169
0.0152
0.0162
0.0138
0.0138
0.0171
0.0158
0.0137
0.0138
0.0161
0.0170
0.0173
0.0147
0.0143
0.0176
0.0186
0.0187
0.0190
0.0202
0.0192
0.0200
0.0218
0.0260
0.0297
0.0292
0.0325
0.0447
0.0318
0.0250
0.0220
0.0239
0.0201
0.0186
0.0221
0.0253
0.0303
0.0312
0.0242
Table 7.1 continued
1956.0540
1956.0155
1955.9770
1955.9386
1955.9001
1955.8616
1955.8231
1955.7847
1955.7462
1955.7077
1955.6692
1955.6308
1955.5923
1955.5538
1955.5153
1955.4769
1955.4384
1955.3999
1955.3614
1955.3230
1955.2845
1955.2460
1955.2076
1955.1691
1955.1306
1955.0921
1955.0537
1955.0152
1954.9767
1954.9382
1954.8998
1954.8613
1954.8228
1954.7843
1954.7459
1954.7074
1954.6689
1954.6304
1954.5920
1954.5535
1954.5150
1954.4765
1954.4381
1954.3996
1954.3611
1954.3226
1954.2842
1954.2457
1954.2072
1954.1687
1954.1303
1954.0918
1954.0533
-----------------------------------------------------------------------------------------------------------
3.3700
3.3629
3.4006
3.4099
3.3913
3.3601
3.3582
3.3275
3.3461
3.4447
3.4332
3.5867
3.6671
3.4415
3.3994
3.6309
3.5857
3.6210
3.6912
3.6912
3.6105
3.5631
3.6008
3.5997
3.4796
3.3726
3.3872
3.3530
3.3258
3.4152
3.3931
3.4346
3.4506
3.4551
3.5353
3.5616
3.5549
3.5153
3.5502
3.5481
3.5488
3.5420
3.5940
3.6017
3.6607
3.7187
3.6591
3.6814
3.7398
3.6880
3.6363
3.5704
3.4773
254
0.4949
0.4760
0.5097
0.5700
0.6336
1.0013
1.0642
0.9529
0.7682
0.7482
0.5615
0.4006
0.3846
0.4216
0.4784
0.5285
0.4948
0.4966
0.5573
0.5578
0.5423
0.5266
0.5065
0.4966
0.4795
0.5168
0.6046
0.6457
0.6446
0.6574
0.8056
0.8229
0.7992
0.7445
0.6381
0.5466
0.4930
0.4831
0.4718
0.4486
0.4263
0.4369
0.4668
0.5323
0.5953
0.6133
0.6191
0.6438
0.6299
0.6256
0.6625
0.7227
0.7498
0.0200
0.0185
0.0169
0.0183
0.0189
0.0174
0.0149
0.0147
0.0139
0.0111
0.0114
0.0141
0.0151
0.0146
0.0140
0.0189
0.0190
0.0218
0.0252
0.0243
0.0232
0.0252
0.0293
0.0351
0.0379
0.0371
0.0342
0.0242
0.0197
0.0157
0.0156
0.0161
0.0165
0.0175
0.0186
0.0217
0.0213
0.0207
0.0201
0.0205
0.0198
0.0176
0.0168
0.0200
0.0295
0.0383
0.0446
0.0351
0.0342
0.0368
0.0372
0.0331
0.0270
Table 7.1 continued
1954.0149
1953.9764
1953.9379
1953.8994
1953.8610
1953.8225
1953.7840
1953.7455
1953.7071
1953.6686
1953.6301
1953.5916
1953.5532
1953.5147
1953.4762
1953.4377
1953.3993
1953.3608
1953.3223
1953.2838
1953.2454
1953.2069
1953.1684
1953.1299
1953.0915
1953.0530
1953.0145
1952.9761
1952.9376
1952.8991
1952.8606
1952.8222
1952.7837
1952.7452
1952.7067
1952.6683
1952.6298
1952.5913
1952.5528
1952.5144
1952.4759
1952.4374
1952.3989
1952.3605
1952.3220
1952.2835
1952.2450
1952.2066
1952.1681
1952.1296
1952.0911
1952.0527
1952.0142
-----------------------------------------------------------------------------------------------------------
3.3753
3.3657
3.3210
3.3677
3.3543
3.3771
3.3883
3.3887
3.3525
3.3305
3.3665
3.4250
3.4496
3.4199
3.4572
3.4498
3.4865
3.6271
3.7104
3.7201
3.7999
3.8984
3.9255
3.7407
3.6449
3.6910
3.6310
3.5715
3.5744
3.6258
3.7197
3.8002
3.9892
4.3149
4.3785
3.9579
3.8397
3.8986
3.6914
3.8137
3.9530
3.9879
3.9757
4.0220
4.1051
4.1328
4.1657
4.2065
3.6770
3.4024
3.2578
3.3362
3.3800
255
0.6981
0.6517
0.6335
0.6272
0.6275
0.6233
0.6480
0.7066
0.7573
0.8575
0.9356
0.8619
0.7958
0.8156
0.5818
0.4747
0.4093
0.3925
0.4570
0.4536
0.5161
0.6111
0.6771
0.7134
0.7949
0.9405
1.0616
0.9600
0.8549
0.9138
1.0887
1.3173
1.3456
1.2843
1.5137
1.3944
0.8779
0.8185
0.7781
0.7059
0.6583
0.6164
0.6047
0.6705
0.7398
0.7388
0.7559
0.9102
0.8184
0.7367
0.7517
0.8877
0.7238
0.0194
0.0160
0.0133
0.0126
0.0118
0.0126
0.0136
0.0133
0.0114
0.0105
0.0125
0.0151
0.0163
0.0161
0.0202
0.0198
0.0195
0.0201
0.0171
0.0171
0.0184
0.0212
0.0209
0.0233
0.0265
0.0256
0.0234
0.0217
0.0222
0.0222
0.0233
0.0254
0.0281
0.0295
0.0273
0.0285
0.0241
0.0215
0.0205
0.0233
0.0228
0.0266
0.0271
0.0241
0.0224
0.0260
0.0254
0.0268
0.0290
0.0212
0.0267
0.0229
0.0272
Table 7.1 continued
1951.9757
1951.9372
1951.8988
1951.8603
1951.8218
1951.7834
1951.7449
1951.7064
1951.6679
1951.6295
1951.5910
1951.5525
1951.5140
1951.4756
1951.4371
1951.3986
1951.3601
1951.3217
1951.2832
1951.2447
1951.2062
1951.1678
1951.1293
1951.0908
1951.0523
1951.0139
1950.9754
1950.9369
1950.8984
1950.8600
1950.8215
1950.7830
1950.7446
1950.7061
1950.6676
1950.6291
1950.5907
1950.5522
1950.5137
1950.4752
1950.4368
1950.3983
1950.3598
1950.3213
1950.2829
1950.2444
1950.2059
1950.1674
1950.1290
1950.0905
1950.0520
1950.0135
1949.9751
-----------------------------------------------------------------------------------------------------------
3.4931
3.6010
3.6066
3.5864
3.5405
3.5166
3.5125
3.5523
3.6312
3.6814
3.7559
3.7525
3.7597
3.8430
3.9414
3.9750
3.8868
3.9226
3.9869
4.0151
3.9657
4.0288
4.0969
4.0912
4.0121
3.8959
3.8369
3.6995
3.6071
3.5685
3.6034
3.6817
3.6601
3.6054
3.5513
3.5078
3.5023
3.5176
3.4890
3.5068
3.6742
3.8569
4.0170
4.1044
4.1717
4.1435
4.0858
4.0964
4.0174
3.9250
3.8424
3.8422
3.8355
256
0.6742
0.6677
0.6328
0.5927
0.5776
0.5805
0.6202
0.6441
0.5928
0.4981
0.4534
0.4423
0.4312
0.4302
0.4389
0.4567
0.4778
0.5078
0.5149
0.4998
0.5004
0.5440
0.5959
0.6215
0.6127
0.5942
0.6280
0.7051
0.7724
0.8422
1.4338
1.3990
1.0671
0.7663
0.7780
0.7854
0.7921
0.7563
0.7315
0.7088
0.6586
0.5966
0.5076
0.4281
0.3539
0.3651
0.3926
0.4004
0.4212
0.4790
0.5228
0.5753
0.6274
0.0322
0.0351
0.0339
0.0334
0.0343
0.0418
0.0472
0.0457
0.0370
0.0310
0.0278
0.0234
0.0208
0.0215
0.0234
0.0244
0.0252
0.0268
0.0303
0.0287
0.0259
0.0254
0.0292
0.0315
0.0314
0.0313
0.0388
0.0306
0.0322
0.0433
0.0430
0.0366
0.0338
0.0268
0.0206
0.0164
0.0170
0.0200
0.0204
0.0169
0.0154
0.0189
0.0203
0.0219
0.0244
0.0263
0.0248
0.0212
0.0180
0.0159
0.0155
0.0157
0.0160
Table 7.1 continued
1949.9366
1949.8981
1949.8596
1949.8212
1949.7827
1949.7442
1949.7057
1949.6673
1949.6288
1949.5903
1949.5519
1949.5134
1949.4749
1949.4364
1949.3980
1949.3595
1949.3210
1949.2825
1949.2441
1949.2056
1949.1671
1949.1286
1949.0902
1949.0517
1949.0132
1948.9747
1948.9363
1948.8978
1948.8593
1948.8208
1948.7824
1948.7439
-----------------------------------------------------------------
3.8246
3.7625
3.7246
3.7378
3.7122
3.6773
3.6342
3.6364
3.5592
3.5509
3.3909
3.2102
3.3261
3.6343
3.7647
3.7415
3.6408
3.7265
3.7315
3.9052
3.9232
3.9178
4.0352
4.1599
3.8144
3.7810
3.6880
3.5182
3.6122
3.7028
3.7022
3.7178
257
0.6760
0.6832
0.6923
0.7078
0.7466
0.8095
0.8620
0.8879
0.8780
0.8879
0.7873
0.7360
0.7015
0.6097
0.5670
0.5031
0.4856
0.5020
0.4746
0.4889
0.5683
0.5148
0.5625
0.8206
1.1137
0.9550
0.7219
0.5223
0.4499
0.5801
0.8066
0.8302
0.0162
0.0162
0.0173
0.0164
0.0164
0.0162
0.0173
0.0175
0.0186
0.0212
0.0240
0.0140
0.0130
0.0325
0.0460
0.0454
0.0375
0.0356
0.0385
0.0369
0.0287
0.0287
0.0386
0.0471
0.0424
0.0384
0.0294
0.0209
0.0212
0.0195
0.0240
0.0362
APPENDIX D
MONTHLY SMOOTHED RIVER DISCHARGE AND CORAL TRACE
ELEMENT DATA
258
Modified
Julian Date
(year)
2004.7623
2004.6219
2004.4816
2004.3413
2004.2009
2004.0606
2003.9202
2003.7799
2003.6396
2003.4992
2003.3589
2003.2186
2003.0782
2002.9379
2002.7976
2002.6572
2002.5169
2002.3766
2002.2362
2002.0959
2001.9556
2001.8152
2001.6749
2001.5346
2001.3942
2001.2539
2001.1136
2000.9732
2000.8329
2000.6926
2000.5522
2000.4119
2000.2716
2000.1312
1999.9909
1999.8505
1999.7102
1999.5699
1999.4295
1999.2892
1999.1489
1999.0085
1998.8682
1998.7279
1998.5875
1998.4472
Rio Fajardo
Discharge
(m3 s-1)
1.3076
1.9999
2.6019
2.9385
2.8045
3.1390
3.4608
3.6169
2.6710
1.6553
1.8151
1.4553
1.8151
1.7114
1.6071
1.4484
1.2192
1.1616
1.8156
1.8639
2.6196
2.6132
1.6996
0.8537
0.9124
0.8749
0.7727
0.7757
1.2375
1.6634
1.3651
0.8527
0.8469
1.1938
3.4774
4.8376
5.0511
3.2900
2.0368
0.9036
1.6082
3.1333
4.4844
4.5656
3.2363
2.4409
Ba/Ca
(μmol mol-1)
3.6169
3.6169
3.7417
4.0466
4.4200
4.9618
4.1208
4.0026
3.8548
3.7608
3.7239
3.6393
3.7010
3.7520
3.7301
3.7300
3.6066
3.5375
3.6995
4.0057
3.9439
3.8200
3.5541
3.5785
3.4870
3.7287
3.8172
3.9641
3.9789
3.8239
3.7830
3.4569
3.5835
3.8429
3.9719
4.1421
4.1669
3.7560
3.4939
3.5790
3.5782
3.5899
3.6951
3.9487
3.9902
3.4677
Table 8.1. Monthly smoothed Rio Fajardo discharge and
coral trace element data presented and discussed in Chapter 4.
259
Table 8.1 continued
1998.3069
1998.1665
1998.0262
1997.8859
1997.7455
1997.6052
1997.4649
1997.3245
1997.1842
1997.0439
1996.9035
1996.7632
1996.6229
1996.4825
1996.3422
1996.2019
1996.0615
1995.9212
1995.7808
1995.6405
1995.5002
1995.3598
1995.2195
1995.0792
1994.9388
1994.7985
1994.6582
1994.5178
1994.3775
1994.2372
1994.0968
1993.9565
1993.8162
1993.6758
1993.5355
1993.3952
1993.2548
1993.1145
1992.9742
1992.8338
1992.6935
1992.5532
1992.4128
1992.2725
1992.1322
1991.9918
1991.8515
1991.7112
1991.5708
1991.4305
1991.2901
1991.1498
1991.0095
1.8513
1.9286
2.2280
2.8616
3.0751
2.4977
1.5956
0.8810
1.2396
1.6756
2.2776
2.7473
2.7478
2.1770
1.4701
1.4778
2.0031
2.3585
2.6955
2.3499
2.1736
1.9431
1.3323
0.9808
1.7701
1.7415
1.5425
0.7492
0.3500
0.4517
0.5785
0.6763
0.7611
1.0062
1.3037
1.4330
1.2233
1.0676
1.6361
1.9341
1.9757
1.3123
1.1578
1.3745
1.3962
1.1398
1.3860
1.4152
1.1248
0.8313
0.8928
0.8074
0.9725
260
3.6082
3.5537
3.6735
3.6567
3.6824
3.6703
3.4211
3.3779
3.6021
3.8660
3.9655
4.0095
3.9160
3.5617
3.4231
3.4433
3.4460
3.4730
3.6457
3.8498
3.6883
3.4510
3.5675
3.8709
4.2300
4.1656
4.0601
3.8933
3.4364
3.3572
3.5212
3.6393
3.7426
3.7476
3.6935
3.6325
3.5314
3.5972
3.6937
3.8539
3.8378
3.6017
3.4711
3.4956
3.5947
3.7370
3.9628
3.7408
3.5127
3.4791
3.5329
3.5847
3.7343
Table 8.1 continued
1990.8691
1990.7288
1990.5885
1990.4481
1990.3078
1990.1675
1990.0271
1989.8868
1989.7465
1989.6061
1989.4658
1989.3255
1989.1851
1989.0448
1988.9045
1988.7641
1988.6238
1988.4835
1988.3431
1988.2028
1988.0625
1987.9221
1987.7818
1987.6415
1987.5011
1987.3608
1987.2204
1987.0801
1986.9398
1986.7994
1986.6591
1986.5188
1986.3784
1986.2381
1986.0978
1985.9574
1985.8171
1985.6768
1985.5364
1985.3961
1985.2558
1985.1154
1984.9751
1984.8348
1984.6944
1984.5541
1984.4138
1984.2734
1984.1331
1983.9928
1983.8524
1983.7121
1983.5718
1.1496
1.6105
1.7629
1.3112
1.3805
1.2573
1.3476
3.5199
4.2431
4.1051
2.1856
1.8733
1.5029
1.9485
2.4241
2.4762
2.4217
2.2162
1.6852
1.3520
1.2720
2.7603
3.4684
3.3549
2.5378
1.7795
2.6633
3.2481
2.8370
1.6357
1.9773
1.8210
1.9208
1.3504
1.6380
1.6704
1.8704
1.9334
2.7254
3.0790
2.5986
1.8115
1.3720
1.5013
1.4564
1.2585
2.2820
2.5944
2.3018
1.5997
1.2382
1.0366
0.9942
261
3.7330
3.6451
3.5687
3.5553
3.5513
3.6106
3.9240
4.0315
4.1701
3.8377
3.5289
3.4791
3.4839
3.5540
3.5954
3.6937
3.7697
3.5602
3.4546
3.5598
3.6624
3.6475
3.7550
3.4851
3.8619
3.9412
3.7183
3.6166
3.6380
3.5763
3.4867
3.4184
3.4361
3.6202
3.7617
3.7325
3.6217
3.4364
3.3974
3.4333
3.5632
3.7401
3.7796
3.6647
3.4611
3.3014
3.2377
3.2477
3.2986
3.3970
3.4512
3.4271
3.4424
Table 8.1 continued
1983.4314
1983.2911
1983.1507
1983.0104
1982.8701
1982.7297
1982.5894
1982.4491
1982.3087
1982.1684
1982.0281
1981.8877
1981.7474
1981.6071
1981.4667
1981.3264
1981.1861
1981.0457
1980.9054
1980.7651
1980.6247
1980.4844
1980.3441
1980.2037
1980.0634
1979.9231
1979.7827
1979.6424
1979.5021
1979.3617
1979.2214
1979.0810
1978.9407
1978.8004
1978.6600
1978.5197
1978.3794
1978.2390
1978.0987
1977.9584
1977.8180
1977.6777
1977.5374
1977.3970
1977.2567
1977.1164
1976.9760
1976.8357
1976.6954
1976.5550
1976.4147
1976.2744
1976.1340
1.5005
1.6619
2.0025
2.7381
2.5317
1.9114
1.4074
1.5689
1.8312
1.8827
1.5617
2.3171
1.9144
1.8312
2.1493
1.8144
1.7368
2.1737
2.5044
2.6174
2.2760
1.8323
2.7411
3.0506
2.5934
1.7179
1.1622
1.4427
1.5089
1.9205
1.8866
1.7853
1.5425
1.6812
3.2048
5.4376
5.8480
5.3599
5.7137
4.1983
3.0872
1.0512
2.4404
3.0540
3.6570
4.0974
2.9665
1.8663
0.9538
0.6841
0.6379
1.1543
1.5005
262
3.4957
3.5288
3.5451
3.5907
3.6061
3.5562
3.5005
3.3913
3.3073
3.3278
3.3633
3.4942
3.6876
3.8033
3.6085
3.4654
3.4196
3.4202
3.3301
3.4273
3.4991
3.6377
3.5698
3.5919
3.7397
4.0646
4.1982
4.0495
3.9223
3.9755
4.2544
4.3189
4.2144
4.6047
3.9920
3.6527
3.9069
4.0047
4.0920
4.3148
4.2418
3.8110
3.5241
3.5452
3.6869
3.8561
4.0714
4.2878
4.3808
4.0801
3.7994
3.9239
4.1200
Table 8.1 continued
1975.9937
1975.8534
1975.7130
1975.5727
1975.4324
1975.2920
1975.1517
1975.0114
1974.8710
1974.7307
1974.5903
1974.4500
1974.3097
1974.1693
1974.0290
1973.8887
1973.7483
1973.6080
1973.4677
1973.3273
1973.1870
1973.0467
1972.9063
1972.7660
1972.6257
1972.4853
1972.3450
1972.2047
1972.0643
1971.9240
1971.7837
1971.6433
1971.5030
1971.3627
1971.2223
1971.0820
1970.9417
1970.8013
1970.6610
1970.5206
1970.3803
1970.2400
1970.0996
1969.9593
1969.8190
1969.6786
1969.5383
1969.3980
1969.2576
1969.1173
1968.9770
1968.8366
1968.6963
1.4169
1.2388
1.6714
2.3791
2.9192
3.6558
2.5426
1.8397
0.6296
0.6363
0.8772
1.2911
3.4409
3.9139
1.9246
0.8044
0.6048
0.9222
1.5043
2.3152
2.3459
2.5967
2.7333
2.5967
1.9683
1.3500
0.9254
0.9903
1.0144
1.0535
1.0850
1.3714
2.1409
3.8779
4.3888
3.8920
2.9916
1.8760
1.4430
2.0570
2.5418
2.8777
3.7505
3.2498
2.7510
1.8586
1.9388
1.6327
1.1748
1.1319
1.4438
1.3099
0.8858
263
4.3184
4.2071
3.9952
3.7344
3.6482
3.6663
3.7609
3.8442
3.9113
3.9763
4.0043
3.9685
3.8067
3.7451
3.7745
3.8616
3.9437
4.0241
4.0292
3.9643
3.9022
3.8863
3.9441
4.0292
3.9687
3.6049
3.5910
3.8650
4.0466
3.9436
3.8184
3.7945
3.8074
3.8231
3.9283
4.1657
4.3614
4.2435
4.1279
4.0002
3.9132
3.9597
4.1396
4.1993
4.1302
3.9993
3.9847
3.9879
3.9724
3.9268
3.8700
3.8394
3.6861
Table 8.1 continued
1968.5560
1968.4156
1968.2753
1968.1350
1967.9946
1967.8543
1967.7140
1967.5736
1967.4333
1967.2930
1967.1526
1967.0123
1966.8720
1966.7316
1966.5913
1966.4509
1966.3106
1966.1703
1966.0299
1965.8896
1965.7493
1965.6089
1965.4686
1965.3283
1965.1879
1965.0476
1964.9073
1964.7669
1964.6266
1964.4863
1964.3459
1964.2056
1964.0653
1963.9249
1963.7846
1963.6443
1963.5039
1963.3636
1963.2233
1963.0829
1962.9426
1962.8023
1962.6619
1962.5216
1962.3812
1962.2409
1962.1006
1961.9602
1961.8199
1961.6796
1961.5392
1961.3989
1961.2586
0.5268
0.6152
0.8523
1.1064
1.2283
1.2118
0.8815
0.7240
0.6732
0.8531
1.3005
1.4327
1.6683
1.7593
1.5892
1.3900
1.2455
1.1811
1.8807
1.9946
2.3936
2.6180
2.0827
2.3417
2.0234
1.4898
1.0176
1.4383
1.6115
1.2265
1.0494
0.8302
0.9675
1.3869
2.4414
2.2618
1.9936
1.5527
1.6661
2.2162
2.8684
2.9966
3.0097
2.6889
1.9049
2.4154
2.6915
2.3095
1.5254
1.2199
1.0429
0.9592
1.0286
264
3.5006
3.4134
3.4474
3.5718
3.5896
3.6911
3.6668
3.5133
3.3236
3.3685
3.4613
3.5779
3.7189
3.7504
3.6786
3.5473
3.5437
3.6099
3.7579
3.8090
3.6922
3.5979
3.5529
3.4786
3.5193
3.6019
3.6115
3.5318
3.5221
3.5712
3.4361
3.2833
3.4615
3.6094
3.5496
3.4959
3.5094
3.5145
3.5270
3.5798
3.6711
3.6302
3.7635
3.6438
3.5585
3.6400
3.7876
3.5586
3.2853
3.1852
3.2700
3.3665
3.5169
Table 8.1 continued
1961.1182
1960.9779
1960.8376
1960.6972
1960.5569
1960.4166
1960.2762
1960.1359
1959.9956
1959.8552
1959.7149
1959.5746
1959.4342
1959.2939
1959.1536
1959.0132
1958.8729
1958.7326
1958.5922
1958.4519
1958.3115
1958.1712
1958.0309
1957.8905
1957.7502
1957.6099
1957.4695
1957.3292
1957.1889
1957.0485
1956.9082
1956.7679
1956.6275
1956.4872
1956.3469
1956.2065
1956.0662
1955.9259
1955.7855
1955.6452
1955.5049
1955.3645
1955.2242
1955.0839
1954.9435
1954.8032
1954.6629
1954.5225
1954.3822
1954.2419
1954.1015
1953.9612
1953.8208
----------------------------------------------------------------------------------------------------------265
3.7642
3.6388
3.3762
3.3059
3.2918
3.3809
3.5104
3.5321
3.4659
3.3064
3.4052
3.3918
3.2335
3.1846
3.2969
3.3407
3.3538
3.3182
3.2643
3.3894
3.5563
3.4591
3.3376
3.2572
3.1563
3.0830
3.0713
3.1162
3.1263
3.2127
3.2786
3.3264
3.3415
3.3259
3.3671
3.5981
3.7595
3.6990
3.4900
3.3793
3.4031
3.4804
3.5609
3.6102
3.5613
3.4385
3.3877
3.4676
3.5181
3.5831
3.6360
3.6688
3.5426
Table 8.1 continued
1953.6805
1953.5402
1953.3998
1953.2595
1953.1192
1952.9788
1952.8385
1952.6982
1952.5578
1952.4175
1952.2772
1952.1368
1951.9965
1951.8562
1951.7158
1951.5755
1951.4352
1951.2948
1951.1545
1951.0142
1950.8738
1950.7335
1950.5932
1950.4528
1950.3125
1950.1722
1950.0318
1949.8915
1949.7511
1949.6108
1949.4705
1949.3301
1949.1898
1949.0495
1948.9091
1948.7688
1948.6285
---------------------------------------------------------------------------
266
3.4068
3.3609
3.3877
3.4197
3.5432
3.7869
3.7650
3.6597
3.8682
4.0431
3.8783
3.9610
3.9753
3.6227
3.4539
3.5234
3.6254
3.7301
3.8603
3.9621
3.9631
3.8688
3.6838
3.5868
3.6093
3.7532
3.9207
3.9994
3.9002
3.7769
3.6708
3.5127
3.5025
3.7158
3.8595
3.9243
3.6448