Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
rsta.royalsocietypublishing.org
Biological response to
millennial variability of dust
and nutrient supply in the
Subantarctic South
Atlantic Ocean
Robert F. Anderson1,2 , Stephen Barker3 ,
Research
Cite this article: Anderson RF, Barker S,
Fleisher M, Gersonde R, Goldstein SL, Kuhn G,
Mortyn PG, Pahnke K, Sachs JP. 2014 Biological
response to millennial variability of dust and
nutrient supply in the Subantarctic South
Atlantic Ocean. Phil. Trans. R. Soc. A 372:
20130054.
http://dx.doi.org/10.1098/rsta.2013.0054
One contribution of 12 to a Theo Murphy
Meeting Issue ‘New models and observations
of the Southern Ocean, its role in global
climate and the carbon cycle’.
Subject Areas:
biogeochemistry, oceanography
Keywords:
Southern Ocean, dust, iron,
biological productivity
Author for correspondence:
Robert F. Anderson
e-mail: [email protected]
Martin Fleisher1 , Rainer Gersonde4 ,
Steven L. Goldstein1,2 , Gerhard Kuhn4 ,
P. Graham Mortyn5 , Katharina Pahnke6
and Julian P. Sachs7
1 Lamont-Doherty Earth Observatory, Columbia University,
PO Box 1000, Palisades, NY 10964, USA
2 Department of Earth and Environmental Sciences,
Columbia University, New York, NY 10027, USA
3 School of Earth and Ocean Sciences, Cardiff University,
Cardiff CF10 3AT, UK
4 Alfred Wegener Institute, Helmholtz Centre for Polar and Marine
Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany
5 Institute of Environmental Science and Technology (ICTA), and
Department of Geography, Universitat Autònoma de Barcelona
(UAB), Edifici Cn, Campus UAB, Bellaterra 08193, Spain
6 Max Planck Research Group, Institute for Chemistry and Biology of
the Marine Environment (ICBM), University of Oldenburg,
Carl-von-Ossietzky-Strasse 9-11, 26129 Oldenburg, Germany
7 School of Oceanography, University of Washington, Seattle,
WA 98195, USA
Fluxes of lithogenic material and fluxes of three
palaeo-productivity proxies (organic carbon, biogenic
opal and alkenones) over the past 100 000 years were
determined using the 230 Th-normalization method
in three sediment cores from the Subantarctic South
Atlantic Ocean. Features in the lithogenic flux record
of each core correspond to similar features in the
record of dust deposition in the EPICA Dome C ice
2014 The Author(s) Published by the Royal Society. All rights reserved.
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
Establishing the contribution by the ocean’s biological pump to past changes in the global
carbon cycle, especially the climate-related changes in atmospheric CO2 concentration [1], is a
long-sought goal of palaeoclimate research (e.g. [2–4]). Biological utilization of nutrients in the
Southern Ocean is particularly important in this regard as it regulates the preformed nutrient
inventory for most of the deep ocean and, therefore, the global average efficiency of the biological
pump [4,5]. Nutrient utilization is inefficient in the Southern Ocean today, in part because
phytoplankton growth is limited by the scarcity of iron (e.g. [6]).
Martin [7] suggested that iron limitation in the Southern Ocean may have been relieved during
the Pleistocene ice ages by the greater deposition of continental mineral aerosols (dust) that
was discovered in Antarctic ice cores. Dust would have supplied iron to marine phytoplankton.
However, early tests of this hypothesis using geochemical indicators of biological productivity
extracted from marine sediment cores concluded that the region south of the Antarctic Polar
Front (APF) was characterized by lower productivity during the ice ages [8–10], contrary to
the expectations from Martin’s hypothesis. The principal exception to this view was derived
by examining the species assemblages of diatoms preserved in glacial-age sediments, which
suggested greater rather than lower ice-age productivity [11]. Despite this one dissenting finding,
the common view is that the increase in dust supply did not enhance biological productivity south
of the APF (for a recent synthesis, see [12]).
In contrast to the Antarctic zone, south of the APF, sediment records from Subantarctic sites
(defined here as the zone north of the APF, extending as far as the Subtropical Convergence)
revealed ice-age enhancement of biological productivity in all sectors of the Southern Ocean
[12,13]. This is particularly true in the South Atlantic, where high levels of productivity are
inferred from sediments deposited during the last ice age [14]. Initial studies concluded that iceage productivity in the Subantarctic South Atlantic was stimulated by dust that originated in
Patagonia [8], immediately ‘upwind’ of the region and known to have been the primary source
of dust in Antarctic ice cores (e.g. [15,16]). However, this view was challenged by a number of
studies concluding that most of the lithogenic material in South Atlantic sediments is delivered
by ocean currents rather than via the atmosphere [17–27], both during ice ages and during
interglacial periods.
Martinez-Garcia et al. [28,29] resurrected the notion that biological productivity in the
Subantarctic South Atlantic is stimulated by dust in finding a tight coupling between dust
and productivity over the past 4 Myr. Specifically, at ODP Site 1090 (42.913◦ S, 8.898◦ E, 3702 m,
figure 1) the accumulation rates of iron and of n-alkanes (organic compounds derived from
leaf waxes of land plants) were correlated with one another across glacial–interglacial cycles,
as well as with geochemical indicators of biological productivity. Each of these parameters in
ODP 1090 sediments was further correlated with dust deposition in the EPICA Dome C (EDC)
ice core. The tight coupling between fluxes of lithogenic material and of leaf waxes, together with
.........................................................
1. Introduction
2
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
core. Biogenic fluxes correlate with lithogenic fluxes in each sediment core. Our preferred
interpretation is that South American dust, most probably from Patagonia, constitutes a
major source of lithogenic material in Subantarctic South Atlantic sediments, and that past
biological productivity in this region responded to variability in the supply of dust, probably
due to biologically available iron carried by the dust. Greater nutrient supply as well as
greater nutrient utilization (stimulated by dust) contributed to Subantarctic productivity
during cold periods, in contrast to the region south of the Antarctic Polar Front (APF), where
reduced nutrient supply during cold periods was the principal factor limiting productivity.
The anti-phased patterns of productivity on opposite sides of the APF point to shifts in
the physical supply of nutrients and to dust as cofactors regulating productivity in the
Southern Ocean.
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
(a)
3
TN057-21
40° S
5
PS2498-1
10
50° S
15
TN057-06/
ODP1090
20
0
25
25
25
25
60° S
60° W
40° W
20° W
0
20° E
(b)
5
30° S
5
(Si)
TN057-21
40° S
5
PS2498-1
TN057-06/ODP1090
5
50° S
5
15
35
25
60° S
60° W
40° W
20° W
45
0
20° E
Figure 1. Location of marine sediment cores discussed in this paper plotted on maps of mean annual concentration of (a) nitrate
[NO3 ] and (b) silicic acid [Si] in surface waters. Maps were prepared using Ocean Data View [30] using data from the World ocean
atlas 2009 [31].
the correlation with EDC dust fluxes, supports the view that most of the lithogenic material in
Subantarctic South Atlantic sediments is supplied as dust [8].
Although the findings of Martinez-Garcia and co-workers are compelling, correlations across
glacial–interglacial cycles may be misleading. Many variables correlate with one another over
100 kyr Milankovitch cycles simply because the enormous variability of climate boundary
conditions influences these variables, without any inherent causal connection among them.
Consequently, here we expand on earlier work by examining South Atlantic sediment records
at much greater temporal resolution, thus affording examination of dust–productivity linkages
in the absence of major changes in climate boundary condition (e.g. glacial–interglacial cycles),
instead focusing on more subtle changes in forcing at higher frequency. We find a tight coupling
between geochemical indicators of biological productivity and the accumulation of lithogenic
material in three cores from the Subantarctic South Atlantic Ocean, and we further demonstrate
that these features exhibit a close correspondence to dust deposition in the EDC ice core on
millennial time scales. We conclude that phytoplankton in the region responded to increased dust
supply with an increase in nutrient utilization and increased export production.
.........................................................
(NO3)
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
30° S
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
2. Material and methods
Lithogenic fluxes in PS2498-1, on the age model of Mackensen et al. [40] (figure 2b), share a number
of features with the EDC dust record (figure 2a); for example, elevated fluxes during the intervals
approximately 18–30 ka and approximately 60–70 ka, as well as three shorter intervals of elevated
flux between 30 and 60 ka. Given the similarity of the records, we selected a number of tie points to
align lithogenic fluxes in PS2498-1 with EDC dust fluxes (solid black lines in figure 2). In addition,
the age model was modified using radiocarbon ages reported by Gersonde et al. [44] for the core
.........................................................
3. Age models
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
Accumulation rates of sedimentary constituents were evaluated for three South Atlantic cores
(figure 1) using the 230 Th-normalization approach [32]. This approach makes a necessary
correction for the redistribution of sediments by deep-sea currents (sediment focusing), which
can cause the local accumulation of sediment to exceed the regional average particle rain
rate by as much as a factor of 20 in the cores studied here [33]. Concentrations of lithogenic
material were estimated for each core using the measured 232 Th concentration. Concentrations
of Th isotopes (230 Th and 232 Th) were measured by isotope dilution using methods described
elsewhere [34,35].
Thorium-232 abundance has a fairly narrow range in upper continental crust [36,37], and
among dust sources worldwide [38]. Here, we use an average content of 10 ppm to estimate
the lithogenic component of each sample, acknowledging that there is a potential uncertainty of
as much as 20% in this estimate depending on the source of the lithogenic material. Assessing
the temporal variability of lithogenic supply is more important here than the absolute flux,
so we accept the uncertainty in the absolute flux inherent in this approach in favour of the
precision that it offers for detecting small changes in the lithogenic flux over time. We make no
initial assumption about the origin of the lithogenic material. Undoubtedly, for each site some
fraction is delivered by ocean currents as well as by dust. We will use the amplitude of the
temporal variability that correlates with dust deposition in the EDC ice core [39] to provide semiquantitative constraints for the fraction of the lithogenic component of sediments that consists
of dust.
Mackensen et al. [40] presented an initial estimate of palaeoproductivity for core PS2498-1
(44.15◦ S, 14.49◦ W, 3783 m). In addition to thorium (see above), we add to the study of PS2498-1
new measurements of organic carbon (C-org, determined at the Alfred Wegener Institute (AWI)),
using an elemental analyser. Biogenic opal was also measured, both at AWI using the method of
Müller & Schneider [41] and at the Lamont-Doherty Earth Observatory (LDEO) using the method
of Mortlock & Froelich [42]. Opal concentrations measured at LDEO were systematically greater
than those measured at AWI, most probably reflecting a difference in the efficiency of Si extraction
[43]. Despite the systematic offset, the downcore pattern of opal content derived using the two
methods was internally consistent. As for the lithogenic fluxes, the precision with which we can
assess temporal variability is more important for our objectives than the accuracy of the opal
flux, so the opal results from LDEO are used without implying any judgement about the relative
accuracy of the two datasets.
Concentrations of C37 alkenones, a suite of organic compounds produced by coccolithophorids,
and thorium have been described previously [33] for TN057-06PC4 (42.91◦ S, 8.9◦ E, 3751 m) and
TN057-21-PC2 (41.13◦ S, 7.81◦ E, 4981 m). Here, we report the summed concentration of the C37
methyl ketones with two (C37:2Me ) and three (C37:3Me ) double bonds, and refer to that quantity
simply as ‘alkenones’. Although more than 10 different alkenones and the related alkenoates
have been reported in marine sediments, C37:2Me and C37:3Me are the two compounds used for
palaeotemperature reconstructions and are by far the most abundant alkenones in Subantarctic
sediments. Those results are supplemented here with additional measurements of thorium for
both cores.
4
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
12
4
1.2
1.0
0.8
(b)
0.6
0.4
0.2
0
0.8
0.6
(c)
0.4
0.2
0
0
10
20
30
40
50
age (ka)
60
70
80
90
TN057-06 lithic flux
(g cm–2 kyr–1)
PS2498-1 lithic flux
(g cm–2 kyr–1)
0
100
Figure 2. (a) Flux of dust in the EPICA Dome C (EDC) ice core [39]. (b) Flux of lithogenic sediment in core PS2498-1 estimated
from 230 Th-normalized fluxes of 232 Th (see text for details) on the original age model of Mackensen et al. [40]. Age control points
used to adjust the age model of PS2498-1 by aligning the lithogenic flux with the EDC dust flux are shown as solid black lines.
(c) Flux of lithogenic sediment in core TN057-06 estimated from 230 Th-normalized fluxes of 232 Th on the age model of C. Charles
(2000, personal communication). Age control points used to adjust the age model of TN057-06 by aligning the lithogenic flux
with the EDC dust flux are shown as dashed grey lines.
top down to a depth of 151 cm (age of 22 ka). The original age–depth relationship for PS24981 is compared with the revised age model in figure 3. Oxygen isotope data for PS2498-1 [40]
placed on the adjusted age model fitted the stacked record of Lisiecki et al. [45], the benchmark
for Pleistocene chronology of deep-sea sediments, at least as well as when using the original age
model (not shown, but available from the lead author).
For TN057-06PC4, we began with the age model of Hodell et al. [46] as modified by C. Charles
(2000, personal communication). Further adjustments to the age model were made to align the
lithogenic fluxes of TN057-06-PC4 with dust deposition in the EDC record (figure 2, dashed grey
lines). As for PS2498-1, the oxygen isotope record for the adjusted age model fitted the Lisiecki
stack at least as well as with the original. The revised age–depth relationships for PS2498-1 and
TN057-06 exhibit less variability over time than with the original age models (figure 3). While a
more uniform accumulation rate does not necessarily mean that an age model has been improved,
the internal consistency among all results following the adjustments to these age models (see also
below) supports the use of the new age models.
Several age models have been published for TN057-21-PC2. Building upon previous work
[47,48], we first tied features in the TN057-21 record to features in the oxygen isotope record of the
North GRIP ice core. The absolute age of both records beyond 60 ka was then adjusted by aligning
the North GRIP oxygen isotope record with the northern Alps (NALPS) speleothem record [49],
which has absolute age control from U–Th dating [50]. Adjustments to the age model of the EDC
ice core were then made to place it on the NALPS chronology as well, maintaining the relationship
between EDC and North GRIP developed by previous studies. While further adjustments to the
absolute age of the records may be necessary, more important is that all of the marine and ice
core records used here have been tied to a common age model to facilitate intercomparison of the
various results.
.........................................................
8
5
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
(a)
EDC dust flux
(mg m–2 yr–1)
16
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
(a) 100
6
age (ka)
40
20
0
200
400
600
800
1000
(b) 120
age (ka)
100
80
60
40
20
0
50
100
150
200
depth (cm)
250
300
350
400
Figure 3. Age–depth relationships for (a) PS2498-1 and (b) TN057-06. Original age models from Mackensen et al. [40] for
PS2498-1 and from C. Charles (2000, personal communication) for TN057-06 are shown in grey. Age control points for the
adjusted age models are shown as triangles for PS2498-1 and as squares for TN057-06. For PS2498-1, the revised age model
was fitted to the radiocarbon dates of Gersonde et al. [44] to a depth of 151 cm. Age control points for depths greater than 151 cm
in PS2498-1, and for all depths in TN057-06, were derived by tuning to the EDC dust record (figure 2).
4. Results
Lithogenic fluxes in the three Subantarctic cores are compared with the EDC dust flux record in
figure 4. Fluxes of opal and of C-org in PS2498-1, as well as the lithogenic flux, are shown with the
EDC dust record in figure 5. Alkenone fluxes from TN057-06 and from TN057-21 are presented
in figure 6, together with the lithogenic fluxes from each core, to compare with the EDC dust
record. Alkenone concentrations are also shown in figure 6d to show that variability of the 230 Thnormalized alkenone flux is determined mainly by variability in the concentration of alkenones
rather than by variability of 230 Th-normalized mass flux.
5. Discussion
(a) Sources of lithogenic material
Cores PS2498-1 and TN057-06 were recovered from sites on the eastern flank of the Mid-Atlantic
Ridge [40] and on the Agulhas Ridge [46], respectively. Their location on elevated topography
and their distance from continental margins isolates these sites from turbidites and from contour
currents delivering sediment from continental sources. Therefore, one can have confidence that
lithogenic sediment delivered to these sites was transported either via the atmosphere or by major
ocean currents, such as the Antarctic Circumpolar Current, allowing for minor contributions from
material transported by icebergs.
.........................................................
60
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
80
16
12
0
0.8
0.6
TN057-21 lithic flux
(g cm–2 kyr–1)
(c)
0.4
0.2
0.8
0.6
0
TN057-06 lithic flux
(g cm–2 kyr–1)
PS2498-1 lithic flux
(g cm–2 kyr–1)
4
1.2
1.0
0.8
(b)
0.6
0.4
0.2
0
(d)
0.4
0.2
0
10
20
30
40
50
age (ka)
60
70
80
90
100
16
12
(a)
4
1.2
1.0
0.8
(b)
0.6
0.4
0.2
0
0
12
10
8
6
4
2
0
PS2498-1 opal flux
(g cm–2 kyr–1)
(c)
0.40
0.30
PS2498-1 C-org flux
(mg cm–2 kyr–1)
PS2498-1 lithic flux
(g cm–2 kyr–1)
8
EDC dust flux
(mg m–2 yr–1)
Figure 4. (a) Flux of dust in the EPICA Dome C ice core [39]. Fluxes of lithogenic sediment in Subantarctic South Atlantic cores
(b) PS2498-1, (c) TN057-06 and (d) TN057-21 estimated from 230 Th-normalized fluxes of 232 Th (see text for details). Age models
for PS2498-1 and TN057-06 were tuned to the EDC dust record as illustrated in figures 2 and 3. The age model for TN057-21 was
derived by tuning to the North GRIP ice core (see text) and, therefore, it is independent of the EDC dust record.
(d )
0.20
0.10
0
10
20
30
40
50
age (ka)
60
70
80
90
100
Figure 5. (a) Flux of dust in the EPICA Dome C ice core [39]. Fluxes of (b) lithogenic sediment, (c) organic carbon and (d) biogenic
opal in Subantarctic South Atlantic core PS2498-1. Fluxes of sediment constituents were estimated by 230 Th normalization (see
text for details).
.........................................................
8
7
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
(a)
EDC dust flux
(mg m–2 yr–1)
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
12
0
(b)
0.6
0.2
0.6
(c)
0.4
0
0.2
3000
2000
0
(d)
1000
1000
800
0
TN057-21 alkenone
(ng cm–2 kyr–1)
(e)
600
2500
400
2000
200
1500
1000
TN057-06 lithic flux
(g cm–2 kyr–1)
0.8
0.4
TN057-06 alkenone
(ng cm–2 kyr–1)
TN057-21 lithic flux
(g cm–2 kyr–1)
TN057-21 alkenone
(ng g–1)
0.8
0
(f)
500
0
10
20
30
40
50
age (ka)
60
70
80
90
100
Figure 6. (a) Flux of dust in the EPICA Dome C ice core [39]. (b) Flux of lithogenic sediment in TN057-21. (c) Flux of lithogenic
sediment in TN057-06. (d) Concentration of alkenones in TN057-21 from [33]. (e) Flux of alkenones in TN057-06 from [51]
supplemented by new 230 Th data. (f ) Flux of alkenones in TN057-21. Records from TN057-21 are in grey to help distinguish
between the two TN057 sediment cores. Fluxes of sediment constituents are estimated by 230 Th normalization (see text
for details).
Lithogenic fluxes in PS2498-1 and in TN057-06 (figure 4b,c) exhibit a close correspondence
to the pattern of dust deposition in the EDC ice core (figure 4a), including two major intervals
of elevated dust flux (approx. 18–35 ka and 60–70 ka), two shorter but intense episodes of dust
deposition centred at approximately 41 ka and at approximately 50 ka, as well as smaller features
(e.g. 55–60 ka and approx. 89 ka). The observed correspondence is consistent with an aeolian
source for a large fraction of the lithogenic material in PS2498-1 and TN057-06. Furthermore,
during intervals of maximum lithogenic flux, fluxes are nearly twice as large on the Mid-Atlantic
Ridge (PS2498-1) as on the Agulhas Ridge (TN057-06), in agreement with previous observations
of an eastward decrease in lithogenic flux across the Subantarctic South Atlantic during the Last
Glacial Maximum (LGM) [8], and consistent with expectations, as dust is washed out of the
atmosphere while transported downwind from a South American source.
In contrast to the other cores, TN057-21 was recovered from a drift deposit in the deep
Cape Basin where contour currents deposit sediment entrained along the margin of Africa
[52]. Mineralogical [22] and isotopic [25] composition of lithogenic material at this location
are consistent with an African source for a portion of the sediment, with an additional timevarying source of material originating at higher latitudes [22]. This combination of two major
sources of lithogenic material at the site of TN057-21 creates a record of lithogenic accumulation
(figure 4d) that has a smaller amplitude of variability compared with the other cores (figure 4b,c).
.........................................................
4
8
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
8
EDC dust flux
(mg m–2 yr–1)
16
(a)
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
Biogenic constituents of the sediments are interpreted as indicators of biological production.
Accumulation of biogenic material in marine sediments is influenced by preservation as well
as by production, and preservation is difficult to quantify. Therefore, rather than attempt to
quantify preservation, we employed two biogenic tracers (opal and organic carbon) for which
preservation is not expected to covary. Preservation of opal is sensitive to temperature, but in
the cold stable environment of the abyssal ocean the preservation of opal depends mainly on
sediment accumulation rate [53]. Preservation of organic carbon, on the other hand, is most
sensitive to the concentration of oxygen in bottom water [54], which is not expected to covary
with sediment accumulation rate. Therefore, covariability of opal and of C-org is interpreted to
reflect changes in production rather than variable preservation.
Accumulation rates of C-org (figure 5c) and of opal (figure 5d) in PS2498-1 are correlated
with one another, as well as with the accumulation rate of lithogenic material (figure 5b) and
with EDC dust deposition (figure 5a). For the eastern sites (TN057 cores), we use alkenones,
long-chained ketones produced exclusively by certain haptophyte algae, predominantly the
coccolithophorids Emiliana huxleyi and Gephyrocapsa oceanica in the open ocean [55,56], as a
palaeoproductivity indicator (figure 6). Alkenones were also employed as a palaeoproductivity
indicator by Martinez-Garcia et al. [28,29] in their study of ODP1090 (figure 1). Features in TN05706 are less well defined because of the roughly fivefold lower accumulation rate in this core
compared with TN057-21, which allows for greater smoothing of the record by bioturbation.
Nevertheless, despite the differing depositional regimes (pelagic deposition on a topographical
elevation versus deep drift deposit), the principal features of the TN057-06 alkenone record
(figure 6e) are consistent with those in TN057-21 (figure 6d,f , [33]), supporting the validity of
these tracers as indicators of time-varying changes in biological productivity.
Palaeoproductivity proxy records in each Subantarctic core exhibit features that covary with
the lithogenic flux in the same sediment core, even over millennial time scales (figures 5 and 6).
Tight coupling over short time intervals lessens the potential influence of changes in global
climate boundary conditions, thereby strengthening the view that the productivity record reflects
a biological response to varying supply of dust, and to the iron that it carries [8,28]. However,
factors other than dust may also regulate biological productivity in the Southern Ocean, and these
are discussed in the next section.
Before proceeding, we want to reiterate that, whereas the age models for PS2498-1 and
TN057-06 were adjusted by tuning to the EDC dust record, the age model for TN057-21 was
tuned only by alignment with the oxygen isotope record of the North GRIP ice core [49].
Therefore, the correspondence of the palaeoproductivity record of TN057-21 (figure 6d,f ) with
the records from the other cores (figures 5 and 6), as well as with the EDC dust record
(figure 6a), supports the reliability of tuning the age models of PS2498-1 and TN057-06 to the EDC
dust record.
.........................................................
(b) Biological response to dust
9
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
Building on the prior work of Kuhn & Diekmann [22], we interpret the record of lithogenic
accumulation in TN057-21 to reflect a time-varying aeolian component, similar to the record
in TN057-06, superimposed on a relatively constant source of sediment from Africa. Despite
its reduced amplitude of variability, the record of lithogenic flux in TN057-21 contains most
of the features that correspond to the EDC dust record, including some of the smaller peaks
(e.g. approx. 30 ka).
Our results do not permit us to quantify precisely the fraction of lithogenic material in
the marine cores that was delivered as dust. Future studies involving geochemical provenance
tracers will help in this regard. Nevertheless, based on our finding that the principal features in
the lithogenic flux record correspond to features in the EDC dust record, we conclude that the
majority of the lithogenic material in PS2498-1 and in TN057-06, as well as a large fraction of
lithogenic material in TN057-21, was delivered by atmospheric transport, most probably from
South America.
0
–0.6
0.2
0.6
1.0
10
20
30
40
50
age (ka)
60
70
80
90
G. bulloides d13C
–0.2
10
1.4
100
Figure 7. Concentration of alkenones (grey) and δ13 C of planktonic foraminifera G. bulloides (black) in TN057-21. Alkenone
concentrations are from [33] and carbon isotope data are from [59].
(c) Supply and utilization of nutrients
The Subantarctic zone is a region of persistently high nitrate concentrations (figure 1a; phosphate,
not shown, has a similar distribution). Therefore, the greater fluxes of organic material during
periods of elevated dust flux, which correspond to the colder intervals in Antarctica [39], could
reflect a more efficient utilization of nitrate due to relief from iron limitation, or a greater
supply of nutrients, or both. Nitrogen isotopes in foraminifera-bound organic matter from
ODP1090/TN057-06 have been interpreted recently to indicate greater nitrate utilization efficiency
during periods of elevated dust supply [57], providing compelling evidence for iron fertilization.
Although the results presented here are consistent with a strong sensitivity of biological
productivity to dust supply in the Subantarctic South Atlantic Ocean, dust supply cannot be the
sole factor regulating productivity. For example, all of the core sites are located in regions where
surface waters today are impoverished in dissolved silicon (Si, figure 1b). At the site of PS24981, the flux of opal during the late glacial period (20–35 ka; 0.25–0.30 g cm−2 kyr−1 ) was about
sixfold greater than during the last 10 kyr (approx. 0.05 g cm−2 kyr−1 ; figure 5d). Nearly identical
results were reported previously for a site further to the east (PS2082-2, 43◦ 13.2 S, 11◦ 44.3 E, [9]).
Substantially greater opal fluxes during the LGM are recorded at sites further south, but still well
to the north of the APF (approx. 50◦ S in this region), ranging between 0.6 g cm−2 kyr−1 (PS17541/-2, 46◦ 46.2 S, 7◦ 36.7 E, [9]) and 1.6 g cm−2 kyr−1 (RC15-93, 46◦ 06 S, 13◦ 13 W, [8]). Opal fluxes
this large require a source of Si much greater than exists today to sustain the diatom productivity
implicated by the opal flux.
A greater supply of nutrients to the Subantarctic zone during glacial periods has also been
inferred from the carbon isotopic composition (δ13 C) of planktonic foraminifera in TN057-21
[58,59]. Many of the features in the alkenone record of TN057-21 are correlated with the δ13 C of
Globigerina bulloides in this core, in the sense that increasing productivity corresponds to increasing
concentrations of nutrients (decreasing δ13 C; figure 7). However, δ13 C of planktonic foraminifera
is sensitive to other factors in addition to nutrient concentration (e.g. [60,61]), so a nutrient–
productivity correlation cannot be inferred unambiguously. Furthermore, over two intervals
(approx. 65–60 ka and approx. 18–10 ka), the palaeoproductivity indicator drops dramatically
while the δ13 C remains low (consistent with, but not necessarily requiring, high nutrients).
Over these intervals, the palaeoproductivity indicator correlates much better with dust supply
(figures 5 and 6).
On the other hand, there are occasions when this correlation breaks down. In TN057-21, for
example, alkenone concentrations are relatively high during times of low or declining lithogenic
flux at approximately 39, 48 and 57 ka (figure 6). In PS2498-1, elevated fluxes of opal and of
C-org also persist until approximately 39 ka, despite declining dust flux (figure 5). Each of these
intervals, corresponding to Heinrich Stadials 4, 5 and 5A, coincides with low δ13 C in G. bulloides
(figure 7), which we interpret to indicate that nutrient supply may play at least as great a role
as dust flux in regulating productivity at these times. Enhanced upwelling south of the APF
.........................................................
3500
3000
2500
2000
1500
1000
500
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
alkenone conc. (ng g–1)
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
Subantarctic productivity can now be considered in the context of a substantial body of work
describing patterns of productivity throughout the entire Southern Ocean. In contrast to modern
(Holocene) conditions, when export production south of the APF exceeds that of the Subantarctic
zone, the situation was reversed during the LGM, when export production of the Subantarctic
zone was much greater than to the south of the APF (e.g. [8–10]). Kohfeld et al. [12] provide a
comprehensive synthesis of the evidence for the last glacial period, whereas Jaccard et al. [63]
show that the seesaw pattern of productivity across the APF was a regular response to climate
variability throughout the late Pleistocene.
Two general scenarios have been proposed to explain lower export production of the Antarctic
zone during glacial periods. First, expansion of sea ice during glacial periods [64] may have
limited the growth of phytoplankton in the Antarctic zone (e.g. [10,65]). Implicit in this scenario
is the corollary that a greater fraction of the nutrients upwelled south of the APF would remain
unused and thus be subjected to Ekman transport northward into the Subantarctic zone. That
is, the greater supply of nutrients to the Subantarctic zone during glacial periods could simply
reflect lower utilization in the Antarctic zone superimposed on conditions of upwelling and
surface water transport similar to those that exist today. The principal alternative scenario is that
nutrient supply by upwelling south of the APF was reduced during glacial periods (e.g. [66]),
most probably tied to increased stratification of the polar ocean (for reviews, see [67,68]).
Nitrogen isotopes archived in Southern Ocean sediments have been interpreted to favour
the second hypothesis (reduced nutrient supply). Throughout the Antarctic zone, the nitrogen
isotopic composition of organic compounds preserved within diatom frustules indicates greater
nitrate utilization during glacial periods, coincident with lower export production, compared
with interglacials [69–71]. Relatively efficient utilization of nitrate during glacial periods is
inconsistent with inhibition of phytoplankton growth by sea ice, but it allows for iron fertilization
in response to the greater supply of dust. That is, the lower rate of nutrient supply during glacial
periods trumps the effect of iron fertilization, reducing export production within the Antarctic
zone compared with iron-limited interglacial periods.
The combination of lower supply and greater utilization of nitrate south of the APF during
glacial periods eliminates the northward transport of unused nutrients as the primary source to
fuel Subantarctic productivity. Instead, during glacial periods, nutrients must have been supplied
to the Subantarctic zone by mixing from below.
Today, the zone of maximum upwelling and nutrient supply is located to the south of the
APF [72]. Two scenarios can be envisioned to account for the northward displacement of nutrient
supply during glacial periods. First, the APF may have migrated northward by several degrees of
latitude (reviewed by Gersonde et al. [64]), carrying the band of upwelling with it into latitudes
more favourable for phytoplankton growth. Alternatively, the hydrographic features associated
with the APF may have remained locked roughly in their present position through interaction
with bottom topography [73]. Under this scenario, a northward shift of the southern westerlies
[74] may have decoupled the zone of upwelling from the APF. Upwelling, driven primarily
by wind stress curl in the Subantarctic zone under these conditions, may have ventilated
much shallower layers of the deep ocean than occurs today. While this scenario is speculative,
ventilation of shallower water masses in the Southern Ocean during glacial periods is consistent
with a growing body of evidence for greater mid-depth stratification during the LGM [75,76]. Of
.........................................................
(d) Contrasting conditions across the Antarctic Polar Front
11
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
during these intervals [62] may have injected nutrients into the Subantarctic zone [51] as well
as in the Antarctic zone. We conclude, therefore, that both increased supply of nutrients and
increased nutrient utilization efficiency, stimulated by dust, contributed to the rise in Subantarctic
productivity during cold periods, including relatively cold intervals of millennial duration during
Marine Isotope Stage (MIS) 3 (approx. 30–60 ka) and late MIS 5 (prior to approx. 80 ka) as well as
throughout MIS 2 and 4.
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
Accumulation rates of lithogenic material in three sediment cores from the Subantarctic South
Atlantic Ocean exhibit features over the past 100 000 years that correspond to the pattern of dust
deposition in the EPICA Dome C ice core, indicating that most of the lithogenic material in the
sediments was derived from South American dust sources. Accumulation rates of biogenic opal
and of organic indicators of biological productivity also correlate with the lithogenic fluxes in
these cores. Combining these results with evidence for nutrient utilization [57] and for nutrient
supply, we conclude that export production in the Subantarctic zone was stimulated during cold
periods by the synergistic effects of greater nutrient supply together with increased nutrient
utilization, supported by elevated dust fluxes.
Nutrient supply and export production south of the APF varied in a pattern that was antiphased with their variability in the Subantarctic zone, whereas nutrient utilization was high in
both regions during the LGM and, presumably, during earlier cold intervals as well. Conditions
south of the APF indicate that export production during the LGM was limited more by the supply
of macronutrients than by iron. The anti-phased pattern of nutrient supply on opposite sides of
the APF, combined with the dust fluxes presented here, further indicates that the physical forcing
that brings nutrients to the surface varied almost concurrently with dust supply.
Climate-related shifts in the latitude of the Southern Hemisphere westerlies have been
suggested to influence nutrient supply in the Subantarctic South Atlantic [47,77] as well as in
the Antarctic zone [62]. Meridional shifts in the southern westerlies may also have modulated the
growth and retreat of mountain glaciers in the mid-latitudes of the Southern Hemisphere [78–81],
which, in turn, may have regulated the source of glaciogenic sediments entrained by the winds
as they passed over Patagonia [82]. Thus, a north–south displacement of the southern westerlies
provides a unifying hypothesis that is consistent with the palaeoclimate records described earlier.
Future studies should consider why these features do not appear to be prominent in model
simulations (for recent discussion, see [83,84]).
Acknowledgements. Helpful comments from Wally Broecker, Chris Charles, Joerg Schaefer, Gisela Winckler,
Aaron Putnam and Ben Bostick are much appreciated. Insightful reviews from two anonymous referees
substantially improved the paper. Opal data from PS2498-1 were generated by Patricia Malone, who passed
away while this manuscript was under review. Her many years of support for the palaeoceanography
community at Lamont are much appreciated. She will be dearly missed by many friends and colleagues.
Data accessibility. Results presented here that have not been published previously will be submitted to the
PANGAEA (http://pangaea.de/) and NCDC (http://www.ncdc.noaa.gov/) data archives. Data from core
PS2498-1 are available at PANGAEA DOI via the link: http://doi.pangaea.de/10.1594/PANGAEA.832084.
DOIs for data from cores TN057-21 and TN057-06 are not yet available.
.........................................................
6. Summary and outlook
12
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
course, the two scenarios are not mutually exclusive, as the westerlies and the frontal systems
may have migrated concurrently.
Lastly, we note that the seesaw pattern of nutrient supply across the APF that is evident over
glacial–interglacial cycles is also apparent over much shorter time scales, with some exceptions.
Anderson et al. [62] interpreted opal fluxes to indicate increased upwelling south of the APF
during the most intense Northern Hemisphere stadials of the last glacial cycle, which correspond
to relatively warm Antarctic Isotope Maxima (AIM). Dust fluxes to Antarctica are at relative
minima during AIM events, and peak during the coldest intervals [39]. Therefore, if the lithogenic
fluxes to Subantarctic sites correspond to dust fluxes in Antarctica, then the covariance between
dust, export production and nutrient supply (figures 5–7) indicates maximum supply of nutrients
to the Subantarctic zone during Antarctic cold intervals, opposite to the pattern observed south of
the APF. The principal exceptions, noted in the previous section, occur during Heinrich Stadials
4, 5 and 5A, when nutrient supply to the Subantarctic zone remained high during the transition
into Antarctic warm intervals. Records with greater temporal resolution will be needed to resolve
the precise phasing between temperature, dust, nutrients and productivity at these times.
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
Funding statement. New results reported here were generated with support from the US NSF via award OCE
0823507.
.........................................................
1. Lüthi D et al. 2008 High-resolution carbon dioxide concentration record 650,000–800,000 years
before present. Nature 453, 379–382. (doi:10.1038/nature06949)
2. Broecker WS. 1982 Glacial to interglacial changes in ocean chemistry. Progr. Oceanogr. 11,
151–197. (doi:10.1016/0079-6611(82)90007-6)
3. Archer D, Winguth A, Lea D, Mahowald N. 2000 What caused the glacial/interglacial
atmospheric pCO2 cycles? Rev. Geophys. 38, 159–189. (doi:10.1029/1999RG000066)
4. Sigman DM, Boyle EA. 2000 Glacial/interglacial variations in atmospheric carbon dioxide.
Nature 407, 859–869. (doi:10.1038/35038000)
5. Marinov I, Gnanadesikan A, Toggweiler JR, Sarmiento JL. 2006 The Southern Ocean
biogeochemical divide. Nature 441, 964–967. (doi:10.1038/nature04883)
6. de Baar HJW, Dejong JTM, Bakker DCE, Loscher BM, Veth C, Bathmann U, Smetacek V.
1995 Importance of iron for plankton blooms and carbon dioxide drawdown in the Southern
Ocean. Nature 373, 412–415. (doi:10.1038/373412a0)
7. Martin JH. 1990 Glacial–interglacial CO2 change: the iron hypothesis. Paleoceanography 5, 1–13.
(doi:10.1029/PA005i001p00001)
8. Kumar N, Anderson RF, Mortlock RA, Froelich PN, Kubik P, Dittrich-Hannen B, Suter M. 1995
Increased biological productivity and export production in the glacial Southern Ocean. Nature
378, 675–680. (doi:10.1038/378675a0)
9. Frank M, Gersonde R, Rutgers van der Loeff MM, Bohrmann G, Nürnberg CC, Kubik
PW, Suter M, Mangini A. 2000 Similar glacial and interglacial export bioproductivity in
the Atlantic sector of the Southern Ocean: multiproxy evidence and implications for glacial
atmospheric CO2 . Paleoceanography 15, 642–658. (doi:10.1029/2000PA000497)
10. Chase Z, Anderson RF, Fleisher MQ, Kubik P. 2003 Accumulation of biogenic and lithogenic
material in the Pacific sector of the Southern Ocean during the past 40,000 years. Deep-Sea Res.
II 50, 799–832. (doi:10.1016/S0967-0645(02)00595-7)
11. Abelmann A, Gersonde R, Cortese G, Kuhn G, Smetacek V. 2006 Extensive phytoplankton
blooms in the Atlantic sector of the glacial Southern Ocean. Paleoceanography 21, PA1013.
(doi:10.1029/2005PA001199.)
12. Kohfeld KE, Graham RM, de Boer AM, Sime LC, Wolff EW, Le Quéré C, Bopp L. 2013 Southern
Hemisphere westerly wind changes during the Last Glacial Maximum: paleo-data synthesis.
Quat. Sci. Rev. 68, 76–95. (doi:10.1016/j.quascirev.2013.01.017)
13. Lamy F et al. 2014 Increased dust deposition in the Pacific Southern Ocean during glacial
periods. Science 343, 403–407. (doi:10.1126/science.1245424)
14. Anderson RF, Chase Z, Fleisher MQ, Sachs J. 2002 The Southern Ocean’s biological
pump during the Last Glacial Maximum. Deep-Sea Res. II 49, 1909–1938. (doi:10.1016/
S0967-0645(02)00018-8)
15. Basile I, Grousset FE, Revel M, Petit JR, Biscaye PE, Barkov NI. 1997 Patagonian
origin of glacial dust deposited in East Antarctica (Vostok and Dome C) during glacial
stages 2, 4 and 6. Earth Planet. Sci. Lett. 146, 573–589. (doi:10.1016/S0012-821X(96)
00255-5)
16. Delmonte B, Andersson PS, Schoberg H, Hansson M, Petit JR, Delmas R, Gaiero DM, Maggi V,
Frezzotti M. 2010 Geographic provenance of aeolian dust in East Antarctica during Pleistocene
glaciations: preliminary results from Talos Dome and comparison with East Antarctic
and new Andean ice core data. Quat. Sci. Rev. 29, 256–264. (doi:10.1016/j.quascirev.2009.
05.010)
17. Petschick R, Kuhn G, Gingele F. 1996 Clay mineral distribution in surface sediments of the
South Atlantic: sources, transport, and relation to oceanography. Mar. Geol. 130, 203–229.
(doi:10.1016/0025-3227(95)00148-4)
18. Diekmann B. 2007 Sedimentary patterns in the late Quaternary Southern Ocean. Deep-Sea Res.
II Top. Stud. Oceanogr. 54, 2350–2366. (doi:10.1016/j.dsr2.2007.07.025)
19. Diekmann B, Fütterer DK, Grobe H, Hillenbrand CD, Kuhn G, Michels K, Petschick R, Pirrung
M. 2003 Terrigenous sediment supply in the polar to temperate South Atlantic: land–ocean
links of environmental changes during the late Quaternary. In The South Atlantic in the late
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
References
13
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
.........................................................
21.
14
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
20.
Quaternary: reconstruction of material budgets and current systems (eds G Wefer, S Mulitza,
V Ratmeyer), pp. 375–399. Berlin, Germany: Springer.
Diekmann B, Kuhn G. 1999 Provenance and dispersal of glacial-marine surface sediments
in the Weddell Sea and adjoining areas, Antarctica: ice-rafting versus current transport. Mar.
Geol. 158, 209–231. (doi:10.1016/S0025-3227(98)00165-0)
Diekmann B, Kuhn G, Rachold V, Abelmann A, Brathauer U, Futterer DK, Gersonde R,
Grobe H. 2000 Terrigenous sediment supply in the Scotia Sea (Southern Ocean): response
to late Quaternary ice dynamics in Patagonia and on the Antarctic Peninsula. Palaeogeogr.
Palaeoclimatol. Palaeoecol. 162, 357–387. (doi:10.1016/S0031-0182(00)00138-3)
Kuhn G, Diekmann B. 2002 Late Quaternary variability of ocean circulation in the
southeastern South Atlantic inferred from the terrigenous sediment record of a drift deposit in
the southern Cape Basin (ODP Site 1089). Palaeogeogr. Palaeoclimatol. Palaeoecol. 182, 287–303.
(doi:10.1016/S0031-0182(01)00500-4)
Latimer JC, Filippelli GM. 2001 Terrigenous input and paleoproductivity in the Southern
Ocean. Paleoceanography 16, 627–643. (doi:10.1029/2000PA000586)
Latimer JC, Filippelli GM. 2007 Sedimentary iron records from the Cape Basin. Deep-Sea Res.
II Top. Stud. Oceanogr. 54, 2422–2431. (doi:10.1016/j.dsr2.2007.07.022)
Latimer JC, Filippelli GM, Hendy IL, Gleason JD, Blum JD. 2006 Glacial–interglacial
terrigenous provenance in the southeastern Atlantic Ocean: the importance of deep-water
sources and surface currents. Geology 34, 545–548. (doi:10.1130/G22252.1)
Krueger S, Leuschner DC, Ehrmann W, Schmiedl G, Mackensen A, Diekmann B. 2008
Ocean circulation patterns and dust supply into the South Atlantic during the last glacial
cycle revealed by statistical analysis of kaolinite/chlorite ratios. Mar. Geol. 253, 82–91.
(doi:10.1016/j.margeo.2008.04.015)
Noble TL, Piotrowski AM, Robinson LF, McManus JF, Hillenbrand C-D, Bory AJM. 2012
Greater supply of Patagonian-sourced detritus and transport by the ACC to the Atlantic
sector of the Southern Ocean during the last glacial period. Earth Planet. Sci. Lett. 317, 374–385.
(doi:10.1016/j.epsl.2011.10.007)
Martinez-Garcia A, Rosell-Mele A, Geibert W, Gersonde R, Masque P, Gaspari V, Barbante C.
2009 Links between iron supply, marine productivity, sea surface temperature, and CO2 over
the last 1.1 Ma. Paleoceanography 24, PA1207. (doi:10.1029/2008PA001657)
Martinez-Garcia A, Rosell-Mele A, Jaccard SL, Geibert W, Sigman DM, Haug GH. 2011
Southern Ocean dust–climate coupling over the past four million years. Nature 476, 312–315.
(doi:10.1038/nature10310)
Schlitzer R. 2013 Ocean Data View. See http://odv.awi.de/.
Garcia HE, Locarnini RA, Boyer TP, Antonov JI, Zweng MM, Baranova OK, Johnson DR.
2010 World ocean atlas 2009, vol. 4, Nutrients (phosphate, nitrate, and silicate). Washington, DC:
U.S. Government Printing Office.
Francois R, Frank M, Rutgers van der Loeff MM, Bacon MP. 2004 230 Th normalization: an
essential tool for interpreting sedimentary fluxes during the late Quaternary. Paleoceanography
19, PA1018. (doi:10.1029/2003PA000939)
Sachs JP, Anderson RF. 2003 Fidelity of alkenone paleotemperatures in southern Cape Basin
sediment drifts. Paleoceanography 18, 1082. (doi:10.1029/2002PA000862)
Fleisher MQ, Anderson RF. 2003 Assessing the collection efficiency of Ross Sea sediment
traps using 230 Th and 231 Pa. Deep-Sea Res. II 50, 693–712. (doi:10.1016/S0967-0645(02)
00591-X)
Anderson RF et al. 2012 GEOTRACES intercalibration of 230 Th, 232 Th, 231 Pa, and prospects for
10 Be. Limnol. Oceanogr. Methods 10, 179–213. (doi:10.4319/lom.2012.10.179)
Taylor SR, McLennan SM. 1985 The continental crust: its composition and evolution, p. 312.
Oxford, UK: Blackwell Scientific.
Rudnick RL, Gao R. 2003 Composition of the continental crust. In Treatise on geochemistry,
vol. 3, The crust (ed. R Rudnick), pp. 1–64. Oxford, UK: Elsevier-Pergamon.
McGee D, Marcantonio F, Lynch-Stieglitz J. 2007 Deglacial changes in dust flux in the
eastern equatorial Pacific. Earth Planet. Sci. Lett. 257, 215–230. (doi:10.1016/j.epsl.2007.
02.033)
Lambert F, Bigler M, Steffensen JP, Hutterli M, Fischer H. 2012 Centennial mineral dust
variability in high-resolution ice core data from Dome C, Antarctica. Clim. Past 8, 609–623.
(doi:10.5194/cp-8-609-2012)
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
15
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
40. Mackensen A, Rudolph M, Kuhn G. 2001 Late Pleistocene deep-water
circulation in the Subantarctic eastern Atlantic. Glob. Planet. Change 30, 197–229.
(doi:10.1016/S0921-8181(01)00102-3)
41. Müller PJ, Schneider R. 1993 An automated leaching method for the determination of
opal in sediments and particulate matter. Deep-Sea Res. I Oceanogr. Res. Papers 40, 425–444.
(doi:10.1016/0967-0637(93)90140-X)
42. Mortlock RA, Froelich PN. 1989 A simple method for the rapid determination of biogenic
opal in pelagic marine sediments. Deep-Sea Res. A Oceanogr. Res. Papers 36, 1415–1426.
(doi:10.1016/0198-0149(89)90092-7)
43. Conley DJ. 1998 An interlaboratory comparison for the measurement of biogenic silica in
sediments. Mar. Chem. 63, 39–48. (doi:10.1016/S0304-4203(98)00049-8)
44. Gersonde R et al. 2003 Last glacial sea surface temperatures and sea-ice extent in the
Southern Ocean (Atlantic–Indian sector): a multiproxy approach. Paleoceanography 18, 1061.
(doi:10.1029/2002PA000809)
45. Lisiecki LE, Raymo ME. 2005 A Pliocene–Pleistocene stack of 57 globally distributed benthic
δ 18 O records. Paleoceanography 20, PA1003. (doi:10:1029/2004PA001071)
46. Hodell DA, Charles CD, Sierro FJ. 2001 Late Pleistocene evolution of the ocean’s carbonate
system. Earth Planet. Sci. Lett. 192, 109–124. (doi:10.1016/S0012-821X(01)00430-7)
47. Barker S, Diz P, Vautravers MJ, Pike J, Knorr G, Hall IR, Broecker WS. 2009
Interhemispheric Atlantic seesaw response during the last deglaciation. Nature 457,
1097–1102. (doi:10.1038/nature07770)
48. Barker S, Knorr G, Vautravers MJ, Diz P, Skinner LC. 2010 Extreme deepening of the
Atlantic overturning circulation during deglaciation. Nat. Geosci. 3, 567–571. (doi:10.1038/
ngeo921)
49. Barker S, Diz P. Submitted. Timing of the descent into the last ice age determined by the
bipolar seesaw. Paleoceanography.
50. Boch R, Cheng H, Spötl C, Edwards RL, Wang X, Häuselmann P. 2011 NALPS: a
precisely dated European climate record 120–60 ka. Clim. Past 7, 1247–1259. (doi:10.5194/
cp-7-1247-2011)
51. Sachs JP, Anderson RF. 2005 Increased productivity in the subantarctic ocean during Heinrich
events. Nature 434, 1118–1121. (doi:10.1038/nature03544)
52. Tucholke BE, Embley RW. 1984 Cenozoic regional erosion of the abyssal sea floor off
South Africa. In Interregional unconformities and hydrocarbon accumulation (ed. JS Schlee).
AAPG Memoir, no. 36, pp. 145–164. Woods Hole, MA: American Association of Petroleum
Geologists.
53. Sayles FL, Martin WR, Chase Z, Anderson RF. 2001 Benthic remineralization and burial
of biogenic SiO2 , CaCO3 , organic carbon and detrital material in the Southern Ocean
along a transect at 170◦ west. Deep-Sea Res. II 48, 4323–4383. (doi:10.1016/S0967-0645(01)
00091-1)
54. Hartnett HE, Keil RG, Hedges JI, Devol AH. 1998 Influence of oxygen exposure time
on organic carbon preservation in continental margin sediments. Nature 391, 572–574.
(doi:10.1038/35351)
55. Sachs JP, Schneider R, Eglinton TI, Freeman K, Ganssen G, McManus J, Oppo D. 2000
Alkenones as paleoceanographic proxies. Geochem. Geophys. Geosyst. 1, 2000GC000059.
(doi:10.1029/2000GC000059)
56. Herbert TD. 2001 Review of alkenone calibrations (culture, water column, and sediments).
Geochem. Geophys. Geosyst. 2, 2000GC000055. (doi:10.1029/2000GC000055)
57. Martinez-Garcia A, Sigman DM, Ren H, Anderson RF, Straub M, Hodell DA, Jaccard SL,
Eglinton TI, Haug GH. 2014 Iron fertilization of the Subantarctic Ocean during the last ice
age. Science 343, 1347–1350. (doi:10.1126/science.1246848)
58. Ninnemann US, Charles CD. 1997 Regional differences in Quaternary Subantarctic nutrient
cycling: link to intermediate and deep water ventilation. Paleoceanography 12, 560–567.
(doi:10.1029/97PA01032)
59. Mortyn P, Charles CD, Hodell DA. 2002 Southern Ocean upper water column structure over
the last 140 kyr with emphasis on the glacial terminations. Glob. Planet. Change 34, 241–252.
(doi:10.1016/S0921-8181(02)00118-2)
60. Spero HJ, Bijma J, Lea DW, Bemis BE. 1997 Effect of seawater carbonate concentration on
foraminiferal carbon and oxygen isotopes. Nature 390, 497–500. (doi:10.1038/37333)
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
16
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
61. Kohfeld KE, Anderson RF, Lynch-Stieglitz J. 2000 Carbon isotopic disequilibrium in
polar planktonic foraminifera and its impact on modern and Last Glacial Maximum
reconstructions. Paleoceanography 15, 53–64. (doi:10.1029/1999PA900049)
62. Anderson RF, Ali S, Bradtmiller LI, Nielsen SHH, Fleisher MQ, Anderson BE, Burckle LH.
2009 Wind-driven upwelling in the Southern Ocean and the deglacial rise in atmospheric
CO2 . Science 323, 1443–1448. (doi:10.1126/science.1167441)
63. Jaccard SL, Hayes CT, Martinez-Garcia A, Hodell DA, Anderson RF, Sigman DM, Haug GH.
2013 Two modes of change in Southern Ocean productivity over the past million years. Science
339, 1419–1423. (doi:10.1126/science.1227545)
64. Gersonde R, Crosta X, Abelmann A, Armand L. 2005 Sea-surface temperature and
sea ice distribution of the Southern Ocean at the EPILOG Last Glacial Maximum—a
circum-Antarctic view based on siliceous microfossil records. Quat. Sci. Rev. 24, 869–896.
(doi:10.1016/j.quascirev.2004.07.015)
65. Charles CD, Froelich PN, Zibello MA, Mortlock RA, Morley JJ. 1991 Biogenic opal in Southern
Ocean sediments over the last 450,000 years: implications for surface water chemistry and
circulation. Paleoceanography 6, 697–728. (doi:10.1029/91PA02477)
66. Francois R, Altabet MA, Yu EF, Sigman DM, Bacon MP, Frank M, Bohrmann G, Bareille
G, Labeyrie LD. 1997 Contribution of Southern Ocean surface-water stratification to
low atmospheric CO2 concentrations during the last glacial period. Nature 389, 929–935.
(doi:10.1038/40073)
67. Sigman DM, de Boer AM, Haug GH. 2007 Antarctic stratification, atmospheric water vapor,
and Heinrich events: a hypothesis for late Pleistocene deglaciations. In Ocean circulation:
mechanisms and impacts (eds A Schmittner, JCH Chiang, SR Hemming), pp. 335–349.
Washington, DC: American Geophysical Union.
68. Sigman DM, Hain MP, Haug GH. 2010 The polar ocean and glacial cycles in atmospheric CO2
concentration. Nature 466, 47–55. (doi:10.1038/nature09149)
69. Sigman DM, Altabet MA, Francois R, McCorkle DC, Gaillard JF. 1999 The isotopic
composition of diatom-bound nitrogen in Southern Ocean sediments. Paleoceanography 14,
118–134. (doi:10.1029/1998PA900018)
70. Robinson RS, Sigman DM. 2008 Nitrogen isotopic evidence for a poleward decrease in
surface nitrate within the ice age Antarctic. Quat. Sci. Rev. 27, 1076–1090. (doi:10.1016/
j.quascirev.2008.02.005)
71. Horn MG, Beucher CP, Robinson RS, Brzezinski MA. 2011 Southern ocean nitrogen
and silicon dynamics during the last deglaciation. Earth Planet. Sci. Lett. 310, 334–339.
(doi:10.1016/j.epsl.2011.08.016)
72. Speer K, Rintoul SR, Sloyan B. 2000 The diabatic Deacon cell. J. Phys. Oceanogr. 30, 3212–3222.
(doi:10.1175/1520-0485(2000)030<3212:TDDC>2.0.CO;2)
73. Matsumoto K, Lynch-Stieglitz J, Anderson RF. 2001 Similar glacial and Holocene Southern
Ocean hydrography. Paleoceanography 16, 445–454. (doi:10.1029/2000PA000549)
74. Toggweiler JR, Russell JL, Carson SR. 2006 Midlatitude westerlies, atmospheric CO2 ,
and climate change during the ice ages. Paleoceanography 21, PA2005. (doi:10.1029/
2005PA001154)
75. Hoffman JL, Lund DC. 2012 Refining the stable isotope budget for Antarctic Bottom Water:
new foraminiferal data from the abyssal southwest Atlantic. Paleoceanography 27, PA1213.
(doi:10.1029/2011PA002216)
76. Lund DC, Adkins JF, Ferrari R. 2011 Abyssal Atlantic circulation during the Last Glacial
Maximum: constraining the ratio between transport and vertical mixing. Paleoceanography 26,
PA1213. (doi:10.1029/2010PA001938)
77. Rodríguez-Sanz L, Mortyn PG, Martínez-Garcia A, Rosell-Melé A, Hall IR. 2012 Glacial
Southern Ocean freshening at the onset of the Middle Pleistocene Climate Transition. Earth
Planet. Sci. Lett. 345–348, 194–202. (doi:10.1016/j.epsl.2012.06.016)
78. Denton GH, Anderson RF, Toggweiler JR, Edwards RL, Schaefer JM, Putnam AE. 2010 The
last glacial termination. Science 328, 1652–1656. (doi:10.1126/science.1184119)
79. Hall BL, Porter CT, Denton GH, Lowell TV, Bromley GRM. 2013 Extensive recession of
Cordillera Darwin glaciers in southernmost South America during Heinrich Stadial 1. Quat.
Sci. Rev. 62, 49–55. (doi:10.1016/j.quascirev.2012.11.026)
80. Kaplan MR et al. 2010 Glacier retreat in New Zealand during the Younger Dryas stadial. Nature
467, 194–197. (doi:10.1038/nature09313)
Downloaded from http://rsta.royalsocietypublishing.org/ on June 16, 2017
17
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 372: 20130054
81. Putnam AE et al. 2013 Warming and glacier recession in the Rakaia valley, Southern
Alps of New Zealand, during Heinrich Stadial 1. Earth Planet. Sci. Lett. 382, 98–110.
(doi:10.1016/j.epsl.2013.09.005)
82. Sugden DE, McCulloch RD, Bory AJM, Hein AS. 2009 Influence of Patagonian glaciers
on Antarctic dust deposition during the last glacial period. Nat. Geosci. 2, 281–285.
(doi:10.1038/ngeo474)
83. Sime LC, Kohfeld KE, Le Quéré C, Wolff EW, de Boer AM, Graham RM, Bopp L. 2013
Southern Hemisphere westerly wind changes during the Last Glacial Maximum: model–data
comparison. Quat. Sci. Rev. 64, 104–120. (doi:10.1016/j.quascirev.2012.12.008)
84. Völker C, Köhler P. 2013 Responses of ocean circulation and carbon cycle to changes in the
position of the Southern Hemisphere westerlies at Last Glacial Maximum. Paleoceanography
28, 726–739. (doi:10.1002/2013PA002556)