Annual Growth Rates and Shell Analysis of Patella vulgata (the common limpet) from
the Sandwick South Site, Unst, Shetland Islands, UK
A Thesis
Presented to
The Faculty of the Department of Biology
Bates College
In partial fulfillment of the requirements for the
Degree of Bachelor of Science
By
Amy Elizabeth Johnston
Lewiston, Maine
April, 2012
This thesis is dedicated to the family and friends who have supported me through this
process I began last May, and who have continued to support me to never give up and
strive to do everything to the best of my ability. Thank you.
2
Acknowledgements
I would like to thank my advisor, Professor William Ambrose, for introducing me
to the many directions of marine ecology, for sharing his knowledge with me, for his
constant support, and for challenging me to be a better marine biologist. I am very
thankful for all of the opportunities Will has given me and am very grateful for the
knowledge I have gained while working at Bates with such an exceptional professor. I
would also like to thank the rest of the Bates community who have assisted me in this
process: Gerald Bigelow for providing my shells, the opportunity to travel to Shetland,
and his assistance and support throughout this process; Bill Locke for his assistance in
lab, help with statistical analysis, and for answering all of my questions; Jennifer Lindelof
for her assistance in the field collecting limpets, support throughout the process, and
being my travel companion to Shetland; Al Wanamaker for running the oxygen isotope
samples in his laboratory; all of my friends for their support; and my parents and sister
for always encouraging me to pursue my love of the ocean and newfound interest in
archaeology.
3
Table of Contents
List of Figures and Tables .................................................................................................... 5
Abstract ............................................................................................................................... 6
1. Introduction .................................................................................................................... 7
2. Methods ........................................................................................................................ 13
2.1. Site Description ...................................................................................................... 13
2.1.1. Sandwick South Archaeological Phases .......................................................... 13
2.1.2. Sandwick South Modern ................................................................................. 13
2.2. Age and Growth ..................................................................................................... 15
2.2.1. Sample Collection and Preparation ................................................................ 15
2.2.2. Annual Growth Determination ....................................................................... 16
2.2.3. Calculation of Growth Rates ........................................................................... 18
2.3. Oxygen Isotopes ..................................................................................................... 18
2.3.1. Sample Preparation ........................................................................................ 18
2.3.2. Sea Surface Temperature ............................................................................... 19
2.4 Statistical Analysis ................................................................................................... 20
2.4.1. Growth Rate .................................................................................................... 20
2.4.2. Oxygen Isotope Data ....................................................................................... 21
3. Results ........................................................................................................................... 21
3.1. Age and Growth ................................................................................................. 21
3.2. Oxygen Isotopes ................................................................................................. 26
3.3. Sea Surface Temperature .................................................................................. 26
4. Discussion...................................................................................................................... 28
Literature Cited ................................................................................................................. 34
Appendix A. Catalog of Shells used for Growth Rate Data ............................................... 37
Appendix B. Catalog of Shells used for Oxygen Isotope Data .......................................... 41
4
List of Figures and Tables
Figure 1. Map of the Shetland Islands with circulation patterns of ocean currents .......... 8
Figure 2. Map of the Island of Unst and the Sandwick South site .................................... 14
Figure 3. Cross section of a Patella vulgata shell ............................................................. 17
Figure 4. Mean apex thickness (± SE) of Patella vulgata .................................................. 22
Figure 5. Mean all SGI (± SE) from Modern 1996 and Modern 2011 ............................... 23
Figure 6. Mean ω (± SE) of Patella vulgata ....................................................................... 24
Figure 7. Mean φ (± SE) of Patella vulgata ...................................................................... 25
Figure 8. 18O (0/00) (±SE) of Patella vulgata ..................................................................... 28
Table 1. Patella vulgata shells from the Sandwick South Site .......................................... 15
Table 2. Estimated mean sea surface temperature.......................................................... 26
5
Abstract
Patella vulgata (common limpet) shells were collected from a Norse site at
Sandwick South, Unst, Shetland Islands, UK, occupied from the 12th to 15th centuries.
Shell growth rate and oxygen isotope data were collected and compared to modern day
shells to provide environmental information across time periods. Growth rate of limpets
from modern day was shown to be significantly higher (~60%) than shells from the 12th/
early 13th century, 14th century, and the House Tephra phase dating to 1362. There was
no difference in growth rates of P. vulgata from modern, modern 1996, and the late
13th/early 14th century. Limpets during most of the Norse occupation grew slower than
modern limpets collected from nearby rocks. This may be due to factors such as: higher
primary productivity and warmer sea surface temperatures at present compared to the
past. Modern shells were ~0.3 O/00 less enriched than shells from most of the
archaeological phases. These oxygen isotopes revealed that modern day temperatures
were significantly different than all of the archaeological phases, except temperatures
from the late 13th/early 14th century. If salinity was held constant, modern day and the
late 13th/early 14th century temperatures may have been warmer than the three other
archaeological phases. These environmental data are being used to determine
environmental changes at the site related to human inhabitance and climate change
information.
6
1. Introduction
Change in climate is a long-term event that can have substantial effects on the
environmental conditions of European coastlines. Climate change is an ongoing issue
that has a large impact on human resources, economy, and ecosystems (Fenger et al.,
2007). Coastline conditions due to past and future environmental change are important
to our understanding of how the climate has changed and how species are affected.
Research in mainland Britain and the Shetland Islands has suggested changes in climate,
agriculture, and fisheries during part of the medieval period (Bigelow, 1987).
Archaeological shell middens suggest early people on the southeast coast of the island
of Unst in the Shetland Islands, Scotland, occupied and relied heavily on the North Sea
coastline for resources since the 12th century (Bigelow, 1985). People in the Shetland
Islands have relied on the coast for resources for thousands of years, while climate
changes have occurred. By studying the archaeological record of such areas, particularly
mollusks found in shell middens from the Shetland Islands, inferences can be made
about environmental conditions from the 12th century to present.
Shetland is an archipelago that lies north of Scotland and west of Norway
(Bigelow, 1987). These islands are known for their maritime climate due to the warm
North Atlantic Drift Current (NADC) and Gulf Stream passing by (Fig. 1) (Birnie et al.,
1993). The close proximity to the ocean and warm ocean currents cause a slightly milder
climate than expected in such northern latitude (Lamb, 1985). Topography and wind
create a treeless island where sunlight hours are
7
Figure 1. Map of the Shetland Islands with circulation patterns of ocean currents.
Blue arrows indicate water of Atlantic origin, while black arrows indicate locally
sourced water.
8
extremely variable throughout the year due to its high latitude (Wheeler and Mays,
1997). The environmental conditions of this area are a key factor for the natural
materials used by the people living in this area (Bigelow, 1985). Early settlers of these
islands also relied on the abundant marine resources and good grazing conditions of the
area. The archaeological site on the island of Unst, is found on the coast, inferring a
higher demand on marine resources instead other resources (Bigelow, 1985).
Biological indicators of environmental change can be used to reconstruct
environmental events and provide information about climate history and present and
future trends in climate change (Lutz and Rhoads, 1980). Throughout the world, marine
invertebrates are subject to seasonal variations in environmental factors including food
availability, photoperiod, dissolved minerals in the water, and temperature (Beukema et
al., 1985). Invertebrates, especially mollusks, are known for recording a continuous
record of growth and life history information, as well as records of environmental
changes in the marine environment (Richardson, 2001). Middens contain shells, along
with other faunal remains, that can be used to study ancient people and the
environmental aspects of an area. Midden shells accumulate over time due to human
activities, especially waste. The physical and chemical variations within midden shells
can be investigated to reconstruct past environmental conditions (Richardson, 2001;
Grocke and Gillikin, 2008).
Controlled by environmental conditions, and biological clocks, shell growth slows
at regular time intervals resulting in the formation of growth lines in some species of
mollusks (Khim, 2003). These growth lines can be studied to determine growth rates of a
9
particular organism. This information can be used to make inferences about ancient and
modern environmental conditions (Beukema et al., 1985; Richardson, 2001; Ambrose et
al., 2006; Carrol et al., 2009). Different time periods of an archaeological site can be
examined using growth information to connect similarities and differences between
environmental conditions, time periods, and rate of growth of individuals.
Oxygen isotopes can also provide information about the environmental
conditions of an area over different time periods. Studies have shown the oxygen
isotopic signature recorded in mollusk shells can be used as a temperature proxy for the
environment during shell growth (Gillikin et al., 2005). This temperature data will
provide important information to interpret differences in growth rate from the different
time periods. By looking at different aspects of shell growth and chemical content, such
as the oxygen isotopic signature, researchers can provide information necessary for
looking at climate change and the changes in the environment. Oxygen isotope analysis
has been conducted on limpets before and has proved to have a high probability of
success. Previous studies have looked at oxygen isotopes and found that once an offset
is taken into account, 18O shell can be reliably used to reconstruct sea surface
temperature in the North Atlantic region (Fenger et al., 2007).
Patella vulgata (the common limpet) is a well-represented species in the
Shetland Islands. This univalve can still be found on rocky shorelines lining the coast of
Europe, today. Limpets were a well represented species in archaeological middens and
are thought to have been collected for both fish bait and as a food source during early
times (Bigelow, 1985). This species is abundant year round and can be easily collected
10
when other food sources are scarce. Their convenience and abundance are likely
reasons for their abundance in an archaeological record in the Shetland Islands.
The archaeological site of Sandwick South has been defined as a Late Norse
settlement on the island of Unst. This period of time, “Late Norse,” falls between 1100
and 1500 A.D. (Bigelow, 1985). This time period preceded that of the medieval period
and falls right after the Viking period of Norse Settlement (Bigelow, 1985). Sandwick
South has been identified as a Late Norse farmstead that was inhabited from the 12 th to
15th centuries. The Sandwick farm was built on previously unsettled land, and later
buried in sand after being abandoned in the 15th century (Bigelow, 1987).
During the time of occupation, the Sandwick South farmhouse was built in two
phases of construction, identified by the presence of a cow byre, main living rooms,
cross passage, and changes in interior layouts over time (Bigelow, 1987). Archaeological
evidence has identified the Sandwick South house as a prime example of the changes in
architecture such houses went through during the Late Norse Period (Bigelow, 1987).
The different phases of occupation and house layout have been dated using radiocarbon
and typological dating methods. Archaeological shells from each of these phases allow
for growth rate and shell analysis to be studied for environmental data and related to
the site occupation.
Information on oxygen isotopes and growth data from these limpet shells will
help us determine the environmental conditions of the area during site occupation in
comparison with today’s conditions. This will help us understand the history of the site
and why the Norse people inhabited it during the specific time frame being studied,
11
related to the resources used during that time. Environmental conditions of the area
and the changes in climate during that time can also give insight into environmental
reasons for why the site was abandoned during the 15th century.
Preliminary information and artifacts has given insight about the Late Norse
economy and marine based lifestyle, but more information is needed to understand the
life history of such an interesting area and group of people that later left the Sandwick
South site before it was buried in sand. Four different archaeological phases have been
identified at the site based upon the house and structural layout of the area that was
discovered during the excavation (Bigelow, 1987). These different phases represent
different periods of time that the main house, surrounding buildings, artifacts, and
shells that have been uncovered at the site, represent.
The objectives of my study were to: (1) use growth rates of P. vulgata to
determine changes in environmental conditions from site occupation during the 12th to
15th centuries to present at Sandwick South, (2) use oxygen isotope analysis of P.
vulgata shells at Sandwick South to examine changes in sea surface temperature since
site occupation. Overall, I will look at the environmental changes in context with the
Norse settlement, determined by shell information from the Sandwick South
archaeological site, compared to known information about changes in climate during
this time period, particularly the Medieval Warm Period and Little Ice Age.
12
2. Methods
2.1 Site Description
2.1.1. Sandwick South: Archaeological Phases
The Sandwick South site is found on the northern-most island, Unst, in the
Shetland Islands (Fig. 2). This archaeological site is located on the southeast coastline of
Unst along the North Sea. This site was excavated during 1970 (Bigelow, 1985). The
Norse house sits above a North Sea beach, with rocky headland with limpets,
gastropods, and other natural fauna, from where it is hypothesized the past people
most likely collected mollusks. This excavation was conducted looking at four different
phases of the site ranging in dates from the 12th to 15th century (Bigelow, 1987). The
four phases of the farmhouse are: Phase 1 (12th/early 13th century), Phase 2 (13th
century), House Tephra (dated to 1362 AD), and Phase 3/Abandonment (late 14th/early
15th century), known from radiocarbon dating.
2.1.2. Sandwick South: Modern
I collected P. vulgata on the Sandwick Unst beaches in June, 2011. Shells were
collected from both the east and west ends of the beach, located below the old
farmstead. Approximately 30 shells were collected from each location. These limpets
were cleaned and the shells were brought back to Bates College, Lewiston, Maine for
further analysis. Modern shells were also collected in 1996 by Gerald Bigelow and used
for analysis.
13
Figure 2. Map of the Island of Unst, with a close up of the Sandwick South site.
14
2.2 Age and Growth
2.2.1. Sample Collection and Preparation
P. vulgata shells were analyzed from Phase 1, Phase 2, Phase 3/Abandonment,
the House Tephra layer, modern from year 1996, and modern from year 2011. A total of
30 shells were analyzed from each of these archaeological and modern time periods
(Table 1). All shells analyzed for growth rates are cataloged in Appendix A.
Table 1. Summary of P. vulgata shells from the Sandwick South Site and time periods
Time Period (Century)
n
Phase 1 (12th / Early 13th)
30
Phase 2 (13th)
30
House Tephra ( year 1362)
30
Phase 3/A (late 13th/ Early 14th)
30
Modern 1996
30
Modern West Side (year 2011)
30
Modern East Side (year 2011)
30
* Modern West and Modern East were combined for analysis
P. vulgata shells were first sectioned in half using a diamond blade band saw.
The smaller shells were embedded in epoxy resin and cut using a slow speed diamond
saw. The cut surface of the shell was ground with 600, 800, 1200, and 2400 grit
sandpaper, in that order. These ground surfaces were then polished with 0.3 m, and
0.05 m alumina polish. Polished shell surfaces were immersed in Mutvei’s solution to
enhance growth lines and increments (Fenger et al, 2007). The apex of the polished
shells was then imaged using a modular focus microscope at 5x magnification.
15
2.2.2 Annual Growth Determination
Annual growth was determined by measuring along the apex of the imaged shell
s. Annual growth increments, determined by the distance between tips of dark, were
measured on micrographs using NIS Elements Advanced Research Microscopy
Software©, down the axis of greatest growth along the apex of the shell (Fig. 3). The last
year of growth was omitted because it was not a full year of growth. These annual
growth measurements were then used to compare growth rates across the different
time periods and modern day.
16
Figure 3. Cross section of a Patella vulgata shell showing the apex with annual and subannual growth lines indicated.
17
2.2.3. Calculation of Growth Rates
Standard growth curves for P. vulgata for each time period were calculated and
mean SGI for Modern 1996 and Modern 2011 were plotted. Growth data based on apex
measurements from all phases was truncated at: Modern (age 10), Modern 1996 and
Phase 2 (age 9), House Tephra (age 11), Phase 1 and 3/A (age 12); in order to ensure
decent sample size and fit the von Bertalanffy curve well. Measurements of shell growth
were fit to the von Bertalanffy growth function:
Ht=H {1-e[-k(t-t0)]}
where H is the maximum asymptotic shell height, k is a growth constant, Ht is the shell
height, t is shell age, and t0 is shell age when height is zero (Appledoorn, 1980, 1983;
Brousseau and Boglivo, 1987). The growth index (ω) was calculated by taking the first
derivative of the von Bertalanffy growth curve for each as t approaches zero. The overall
growth performance index (') was also calculated:
'= log (k) +2log (H)
which is a quantitative measurement of growth that can be used to compare individual
shells of different ages. In this equation, H is the maximum asymptotic shell height and
k is a growth constant (Pauly and Munro, 1984).
2.3 Oxygen Isotopes
2.3.1. Sample Preparation
Ten shells from each phase were used from Phase 1, Phase 2, Phase
3/Abandonment, House Tephra, and modern day (year 2011) for oxygen isotope
analysis. All shells prepared for oxygen isotope analysis are cataloged in Appendix B.
18
These shells were first scrubbed and lightly ground on a sander to remove any organic
matter. Approximately 0.006 mg of external shell from the last three to four years of
growth was collected from each of the shells. Ages of the shell were determined by
notches in the margin of shell that correspond to annual growth lines in the apex
(Fenger et al. 2007). These 0.006 mg samples were then sent out to Iowa State
University (Department of Geological and Atmospheric Sciences) for oxygen isotope
analysis.
At Iowa State University, oxygen isotope measurements were made using a
Finnigan MAT Delta Plus XL mass spectrometer in continuous flow mode that was
connected to a gas bench with a CombiPAL autosampler. Standards (NBS-18, NBS-19,
LSVEC) were used for isotopic corrections and to assign data to the correct isotopic
scale. One reference standard was used for every five samples. The analytical
uncertainty and average correction factor for δ18O is ± 0.10‰ (VPDB), respectively.
2.3.2. Sea Surface Temperature
Sea surface temperatures were calculated from the δ18O data obtained from the
10 P. vulgata shells from each phase according to the following formula:
1000 lnα = 2.87 x 106/T2 -2.89
Where T is temperature in Kelvin and α is the fractionation between calcite and water
(Fenger et al., 2007). To solve this equation the δ18Oseawater composition for the North
Sea was calculated using the formula:
δ18Oseawater= 0.417S-14.555
19
where S is seawater salinity (Schone et al., 2004). The α value was calculated using the
formula:
(δcalcite +1000)/(δseawater +1000)
where δseawater is expressed in VSMOW (Fenger et al., 2007). To convert δ18Ocalcite values
from VPDB to the VSMOW scale the following equation was used:
δ18OVSMOW=1.03091(δ18OVPDB) + 30.91
by using δcalcite (Fenger et al., 2007). These values were then used in the first question to
solve for sea surface temperature according to each δ18O value. Modern sea surface
temperature was determined by calculating the mean temperature from the years
2000-2011 from the ICES temperature log for the Shetland Islands region (ICES
database).
2.4 Statistical Analyses
Mean ω and mean φ' from each phase as well as δ18O samples were tested for
normality (Shapiro-Wilk) and homoscedastcity (Bartlett’s Test). Distributions for ω were
log transformed in order to pass normality. All other distributions for φ' and δ 18O were
normal and homoscedastic.
2.4.1. Growth Rate
East modern 2011 and west modern 2011 were compared parametrically using a
Two-Sample t-Test to determine if the two sites could be pooled. Mean φ’ for east and
west modern were combined. The mean ω from all time periods was compared
parametrically using a One-way ANOVA and a Tukey’s Multiple Comparison Test. The
mean φ’ from all time periods and combined modern collections were also compared
20
parametrically using a One-way ANOVA and a Tukey’s Multiple Comparison Test. SGI
and modern mean sea surface temperature data were also compared using a linear
regression.
2.4.2. Oxygen Isotope Data
The delta oxygen isotope values from the different phases were compared using
a One-Way ANOVA and a Tukey’s Multiple Comparison Test.
3. Results
3.1 Age and Growth
Growth data based upon apex measurements from P. vulgata from all time
periods was fit to the von Bertalanffy curve (Fig. 4). Standard growth index (SGI) was
determined for Modern 1996 and Modern 2011, showing growth to be mostly higher
than predicted during Modern 2011 (Fig. 5). P. vulgata from Modern 2011 grew
significantly faster than all other phases (Fig. 6). House Tephra shells grew significantly
slower than all other phases (Fig. 6). Growth curves of each phase correlate to the mean
ω results, with Modern 2011 and House Tephra falling on opposite ends of the growth
rate and size scale (Fig. 4, Fig. 6).
Mean  shows that P. vulgata from modern day grew significantly faster than all
those from the archaeological phases, except Phase 2 (Fig. 7). P. vulgata from modern
grew 60% faster than shells from the 12th/early 13th century, 14th century, and the
House Tephra phase dating to 1362. There was no difference in growth rates of P.
vulgata from the two modern groups and the archaeological phase 2 (late 13 th/early
14th century) (Fig. 7).
21
Figure 4. Mean apex thickness (± SE) of Patella vulgata from Phase 1, Phase 2, House
Tephra, Phase 3/A, Modern 1996, and Modern 2011 time periods. All growth curves fit
the Von Bertalanffy curve well, with r2 values shown above.
22
Figure 5. Mean all SGI (± SE) from Modern 1996 and Modern 2011 time periods. An SGI
of 1.0 represents expected growth.
23
Figure 6. Mean ω (± SE) of P. vulgata from Phase 1, Phase 3, House Tephra, Phase 3/A,
Modern 1996, and Modern 2011 time periods. Bars with common letters are not
significantly different from each other (One-Way Annova, p <0.001; Tukey’s Multiple
Comparrison Post Hoc Test p <0.05).
24
Figure 7. Mean φ (± SE) of Patella vulgata from Phase 1, Phase 2, House Tephra, Phase
3/A, Modern 1996, and Modern 2011 time periods. Bars with common letters are not
significantly different from each other (One-Way Annova, p <0.001; Tukey’s Multiple
Comparrison Post Hoc Test p <0.05). The φ equation is also shown.
25
3.2 Oxygen Isotopes
Modern day shells were determined to be approximately 0.3 O/00 less enriched
than shells from most of the archaeological phases (Fig. 8). There was no difference in
enrichment of P. vulgata from modern day and the archaeological phase 2 (late
13th/early 14th century) (Fig. 8).
3.3 Sea Surface Temperature
Sea surface temperatures were calculated from 18O in P. vulgata shells (Fig. 8).
Sea surface temperature has increased by approximately 2.7C from the 12th/ early 13th
century to modern day (Table 2). The modern day mean sea surface temperature in the
Shetland Islands region was determined to be 10.5 C. This mean temperature was
calculated for the years between 2000 and 2011 (ICES database). Modern sea surface
temperature was compared to SGI from Modern 1996 and Modern 2011 data, implying
that temperature explains ~10% of annual variation in growth. The statistical power of
this comparison was too low, however, and results of this comparison were insignificant
(r2=0.156).
Table. 2. Estimated mean sea surface temperature values calculated from 18O in P.
vulgata shells from the Sandwick South Site. Modern sea surface temperature is the
mean sea surface temperature from 2000-2011 from the ICES database for the
Shetland Islands region.
Time Period (Century)
Phase 1 (12th / Early 13th)
Phase 2 (13th)
House Tephra (year 1362)
Phase 3/A (late 13th/ Early 14th)
Modern East Side (year 2011)
Modern (year 2000-2011)
Mean Sea Surface
Temperature (°C)
7.8
8
7.9
7.7
9
10.5
26
Figure 8. 18O (0/00) (±SE) of P. vulgata shells from Phase 1, Phase 2, House Tephra,
Phase 3/A, and Modern 2011 time periods from the Sandwich South Site. Different
letters above bars indicate differences among groups (Tukey’s Multiple Comparrison
Post Hoc Test p <0.05). Mean sea surface temperature for each period, calculated from
δ18O with an assumed salinity of 35.3 ppt, is also shown.
27
4. Discussion
P. vulgata is a species that inhabits rocky shorelines in the high intertidal and
shallow subtidal zones (Fenger et al., 2007). This species has maximum growth during
the early summer and slows growth during the winter (Blackmore, 1969; Lewis
Bowman, 1975, Jenkins and Hartnoll, 2001; Fenger et al., 2007). Major limpet growth
lines can be identified as the largest and most pronounced growth lines visible on the
shell surface and have been correlated to the most positive δ18O values (Fenger et al.,
2007). These observations agree with other sclerochronologic studies of other
molluscan species. The growth rate of other species in the mid to high latitude also
decreases during the winter in relation to food shortage and reproductive processes
(Fenger et al., 2007). Limpet species are known to settle on a home base and move only
very short distances away to feed. The short travel distance of this species allows for the
shell to record environmental conditions (i.e. minimum and maximum temperatures,
reproductive processes, and food supply) from just one location (Fenger et al., 2007).
The Sandwick South site was a small farmhouse and during site occupation, the
inhabitants of the area relied heavily on shellfish for fish bait and as a food source
(Bigelow, 1985). Limpets are well represented in the archaeological record of this site
and were a key resource of the Norse people. The presence of shellfish in the diets of
these people indicates the assurance of survival of a population over a short period of
time (Bigelow, 1985). The high abundance of limpets in the archaeological record of the
site and the use of this species as a food source prior to site abandonment corresponds
to a decline in environmental conditions and the need for shellfish in order to survive.
28
P. vulgata growth rates from all archaeological phases at the Sandwick South site
were significantly lower than the modern 2011 growth rate. Previous studies have
shown several mollusk species growth line formation, corresponding to slower growth,
has been attributed to lower seawater temperatures, but also may be due to biotic
factors (Richardson, 2001). I believe this growth rate difference may be due to
environmental factors such as: higher primary productivity and sea surface
temperatures, and less biotic and abiotic factors at present compared to past site
occupation conditions.
Faster growth rates in P. vulgata during modern time may be due to an increase in
food abundance and quality. This difference would indicate an increase in primary
productivity around the area of the Sandwick South Site. The limpet is known as a
dominant grazer in the mid-intertidal zone of northwest Europe and has an important
role in community structure and the regulation of macroalgae (Jenkins and Hartnoll,
2001). Previous correlations have been made between limpet growth and rate of algal
production, with greater limpet growth on more nutrient rich shores (Bosman and
Hockey, 1988). Rate of primary production in the intertidal is a key factor in the
relationships between species of all trophic levels and the size and life history patterns
of populations of limpets on enriched and unenriched shores (Bosman and Hockey,
1988). Faster growth rates in P. vulgata during modern day might indicate a more
enriched shore and higher rate of algal production compared to past time periods.
The standard growth index (SGI) results indicate Modern 2011 shells grew at a
higher rate than the predicted value of 1.0. Modern 1996 shells fluctuate above and
29
below the predicted growth value of 1.0. Statistical results do not support a correlation
between Modern 2011 SGI and sea surface temperature. A correlation is still possible,
however, because the statistical power of this comparison was very low. A higher
statistical power may show that the ocean currents that bring warmer currents up
above 60° latitude correlate to higher modern SGI values. Variability in the location of
shell collection may also play a role in the SGI values of the modern shells. The Shetland
Islands are presently known for a maritime climate due to this warm North Atlantic Drift
Current and Gulf Stream passing by (Birnie et al., 1993). The close proximity to the
ocean and warm ocean currents cause a slightly milder climate than expected in such
northern latitude (Lamb, 1985). These warmer waters can help to explain the higher
rate of P. vulgate growth in last 10 years.
P. vulgata δ18O analysis indicated an increase, with fluctuations related to
climatic events, in sea surface temperature from 7.8°C in the 12th century to around 9°C
presently. These temperatures were determined with assuming a salinity of 35.3 ppt,
determined from modern sea surface data (ICES database). The growth rates of P.
vulgata determined by ω and φ correlate to the sea surface temperature that was
determined by the δ18O analysis of P. vulgata or sea surface temperature recorded by
ICES database: growth rates of P. vulgata are greater at modern day, 2011, than all the
archaeological phases, except Phase 2 (13th century) in φ analysis, while the sea surface
temperature is presently greater than all of the archaeological phases. The faster
growth of P. vulgata during modern day may be partly due to primarily warmer waters
compared to the temperatures between the 12th and 15th centuries.
30
Previous studies have determined that δ18O is a valuable proxy for climate
reconstruction, but concerns address its reliability during changing δ18Oseawater
conditions. The oxygen isotope composition (and food supply and salinity) of the North
Sea varies during extreme years due to the changing ocean currents of the area (Schone
et al., 2004). Slight changes in δ18Oseawater conditions or salinity can result in precision
error of sea surface temperature reconstruction, however, if δ18O averages are
calculated from annual growth increments, the potential precision error of temperature
reconstruction is minimized and sea surface temperatures can be reconstructed once
an offset is taken into account (Schone et al., 2004).
The Little Ice Age was a climatic period dating between the 1300 and 1850 AD
(Lamb, 1977, Grove 2001). During this time period, records discuss general decreases in
temperature and weather conditions, increases in storminess, and failed crops (Lamb,
1977; Grove, 1988; Grove 2001; Mann et al., 2008). The span of the Little Ice Age from
the 14th to mid 19th century corresponds to the slight decrease in sea surface
temperature during Phase 3/A (late 14th/early 15th century) at the Sandwick South Site
(Table 2). Excavation of the Sandwick South site has implied the occupation of the site
by the Norse from the 12th to 15th centuries before being abandoned for an unknown
reason (Bigelow, 1987). A decline in temperature and weather conditions at the start of
the Little Ice Age may be a key reason for the abandonment of this site during the early
15th century. A decline in mean sea surface temperature from 8°C during Phase 2 to
7.9°C and 7.7°C during House Tephra and Phase 3/A time periods supports a decrease in
temperatures during the Little Ice Age and potential factor for abandonment of the site.
31
The House Tephra phase has been dated to 1362 AD and is known as a very harsh year
in terms of environmental conditions (Bigelow, 1985).
Phase 2 (13th century) shows no significant difference in growth rate (φ) in P.
vulgata shells compared to modern 2011 shells. Mean sea surface temperature from
Phase 2 of 8°C was determined from δ18O analysis, only 1°C colder than modern 2011.
This time period falls during the end of the Medieval Warm Period, dated to between
900 and 1300 AD (Grove and Switsur, 1994; Crowley, 2000; Broecker, 2001). The
Medieval Warm Period is known for warmer temperatures and better weather
conditions, prior to a decline in conditions during the Little Ice Age (Crowley, 2000). The
Medieval Warm Period spans the time the Sandwick South site was occupied during the
13th century. A higher mean sea surface temperature and rate of growth during Phase 2,
compared to other archaeological phases of the site, correspond to an increase in
temperature and growing conditions during the Medieval Warm Period, just before the
Little Ice Age began during the House Tephra and Phase 3/A occupations.
The combination of growth rate and oxygen isotope data from the P. vulgata
shells suggest that sea surface temperatures are currently higher than most of the
archaeological phases from the Sandwick South site. Further studies need to be done of
P. vulgata to develop more information about growth rate across time periods. Oxygen
isotope analyses should be carried out on all phases to validate trends seen in
temperature data. These analyses may help to answer further questions about the
environmental conditions of the area during the specific time periods and relate this
32
information to the Norse occupation and history of the Sandwick South Site in the
Shetland Islands.
33
Literature Cited
Ambrose, W., Carroll, M., Greenacre, S., Thorrolds, S. McMahon, K., 2006. Variation
in Serripes groenlandicus (Bivalvia) growth in a Norwegian high-Arctic fjord:
evidence for local- and large-scale climatic forcing. Global Change Biology.
12: 1595–1607.
Beukema, J.J, Knoll, E., and Cadee, G.C., 1985. Effects of temperature on the length of
the annual growing season of the Tellinid bivalve Macoma balthica (L.) living on
tidal flats in the Dutch Wadden Sea. Journal of Experimental Marine Biology and
Ecology, 90:129-144.
Bigelow, G. F., 1985. Shetland Archaeology: Sandwick, Unst, and Late Norse Shetland
Economy. The Shetland Times Ltd., 96-119.
Bigelow, G. F., 1987. Domestic architecture in Medieval Shetland. Rev. Scott. Cult.
3:23-38
Birnie, J., Gordon, J., Bennett, K., and Hall, A., 1993, The Quaternary of Shetland Field
Guide: Quaternary Research Association, pg. 111.
Blackmore, D. T., 1969. Studies of Patella vulgata L. I. Growth, reproduction, and
zonal distribution, J. Exp. Mar. Biol. Ecol., 3: 200 – 213.
Bosman, A. L., and Hockey, P.A.R., 1988. The influence of primary production rate on
the population dynamics of Patella granularis, an intertidal limpet. Marine
Ecology 9:181–198.
Broecker, W. S., 2001. ‘Was the Medieval Warm Period global?,’ Science 291:1497–
1499.
Carroll M.L., Johnson, B.J., Henkes, G.A., McMahon, K.W., Voronkov, A., Ambrose, W.G.,
and Denisenko SG. (2009). Bivalves as indicators of environmental variation and
potential anthropogenic impacts in the southern Barents Sea. Marine Pollution
Bulletin. 59: 193-206
Crowley, T. J., 2000. Causes of Climate Change Over the Past 1000 Years, Science,
289: 270 – 277
Fenger T, Surge D, Schöne BR, Milner N (2007) Sclerochronology and geochemical
variation in limpet shells (Patella vulgata): a new archive to reconstruct
coastal sea surface temperature. Geochem Geophys Geosys 8:Q07001
doi:10.1029/2006GC001488
34
Gillikin, D. P., De Ridder, F., Ulens, H., Elskens, M., Keppens, E., Baeyens, W., et al.,
2005. Assessing the reproducibility and reliability of estuarine bivalve shells
(saxidomus giganteus) for sea surface temperature reconstruction: Implications
for paleoclimate studies. Palaeogeography, Palaeoclimatology, Palaeoecology,
228(1-2), 70-85.
Grocke, D.R., and Gillikin, D.P., 2008. Advances in mollusk sclerochronology and
sclerochemistry: tools for understanding climate and environment. GeoMarLett. 28: 265-268.
Grove, J.M., 1988, The Little Ice Age: London, Metheun and Co. Ltd., pg. 498.
Grove, J.M., Switsur, R., 1994. Glacial geological evidence for the Medieval Warm
Period. Climatic Change 26, 143–169.
Grove, J.M., 2001. The Initiation of the “Little Ice Age” in Regions Round the North
Atlantic, Climatic Change, 48:53–82.
Jenkins, S. R., and Hartnoll, R.G., 2001. Food supply, grazing activity and growth rate
in the limpet Patella vulgata L: a comparison between exposed and sheltered
shores. Journal of Experimental Marine Biology and Ecology 258:123–139.
Khim B-K, Kranz D.E., Cooper LWet al. (2003) Seasonal discharge to the western
Chukchi Sea shelf identified in stable isotope profiles of mollusk shells. Journal of
Geophysical Research, (108):161 170.
Lamb, H.H., 1977, Climate: Present, Past and Future. Vol. 2: Climatic History and the
Future: London, Methuen, pg. 837.
Lamb, H.H., 1985, The Little Ice Age Period and Storms Within IT, The Climatic
Scene, M.J. Tooley and G.M. Sheail, eds, London: George Allen and Unwin, pg.
104-131.
Lewis, J. R., and Bowman, R. S., 1975. Local habitat-induced variations in the
population dynamics of Patella vulgata L., J. Exp. Mar. Biol. Ecol., 17: 165 – 203.
Lutz, R.A, and Rhoads. D.C, 1980. Growth patterns within the molluscan shell; an
overview. Skeletal growth of aquatic organisms; Biological Records of
Environmental Change. Plenum Press, New York.
.
Mann, M., Zhang, Z., Hughes, M., Bradley, R., Miller, S., Rutherford, S., and Ni, F.,
2008, Proxy-based reconstructions of hemispheric and global surface
35
temperature variations over the past two millennia, PNAS, 105 (36): 1325213257.
Richardson, C.A., 2001. Molluscs as Archives of Environmental Change.
Oceanography and Marine Biology, 39: 103-164
Schone, B.R., Freyre Castro, A.D., Fiebig, J., Houk, S.D., Oschmann, W., Kro¨ncke, I.,
2004. Sea surface water temperatures over the period 1884–1983
reconstructed from oxygen isotope ratios of a bivalve mollusk shell (Arctica I.)
islandica , southern North Sea). Palaeogeogr., Palaeoclimatol., Palaeoecol. 212:
215 – 232.
Wheeler, D., and Mayes, J., 1997. Regional Climates of the British Isles: London,
Routledge, pg. 343.
36
Appendix A. Catalog of Shells used for Growth Rate Data
Phase
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Date
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
Ambrose Lab ID
SU7_222-806_#1
SU7_G1_223-806_#1
SU7_G1_223-806_#4
SU7_G1_223-806_#5
SU7_G1_223-806_#U
SU7_H1_224-806_#4
SU7_H1_224-806_#5
SU7_I1_225-806_#3
SU7_I1_225-806_#4
SU7_I1_225-806_#7
SU7_I1_225-806_#1
SU7_H1_224-806_#3
SU7_I1_225-806_#2
SU7_I1_225-806_#6
SU7_H1_224-806_#2
SU7_H1_224-806_#1
SU7_224-807_#1
SU7_G1_223-806_#6
SU7_G1_223-806_#7
SU7_G1_223-806_#U2
SU7_I1_225-806_#8
SU7_I1_225-806_#9
SU7_I1_225-806_#13
SU7_I1_224-806_#7
SU7_224-807_#2
SU7_G1_223-806_#2
SU7_I1_225-806_#5
SU7_H1_224-806_#7
SU7_H1_224-806_#6
SU7_224-807_#1
222-806_atBaulk221_#2
223-806_Su5_G1_#3
223-806_SU5_G1_#4
223-806_Su5_G1_#5
223-806_SU5_G1_#6
223-806_SU5_G1_#8
223-806_SU5_G1_#9
223-806_SU5_G1_#U
223-806_SU6_#1
224-806_SU6_H1_#1
37
Phase
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
Phase 2
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
Date
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
13th Century
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
Ambrose Lab ID
224-806_Su6_H1_#2
224-806_SU6_H1_#3
224-806_SU6_H1_#4
224-806_SU6_H1_#5
224-806_SU6_H1_#6
224-806_SU6_H1_#7
224-806_SU6_H1_#8
224-806_SU6_H1_#9
224-806_Su6_H1_#10
225-806_SU6_I1_U2
225-806_SU6_I1_#2
225-806_SU6_I1_#U
225-806_Su6_I1_#U3
218-797_SCR_SU3_#1
phase2_U1
phase2_U2
phase2_U3
phase2_U4
phase2_U5
phase2_U6
H3_231-799_#1
H3_231-799_#2
H3_231-799_#3
H3_231-799_#4
H3_231-799_#5
H3_231-799_#6
H3_231-799_#7
H3_231-799_#8
H3_231-799_#9
H3_231-799_#10
H3_232-799_#1
H3_232-799_#2
H3_232-799_#3
H3_232-799_#4
H3_232-799_#5
H4_230-801_#1
H4_230-801_#2
H4_230-801_#3
H4_230-801_#4
H4_230-801_#5
H4_231-801_#1
H4_231-801_#3
38
Phase
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Date
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
1362 AD
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
late 14th/15th Century
year 1996
year 1996
year 1996
year 1996
Ambrose Lab ID
H4_231-801_#4
H4_231-801_#5
H4_SCR_230-801_#1
H4_Scr_230-801_#2
H4_SCR_230-801_#3
H4_SCR_230-801_#4
H4_SCR_231-801_#2
H2_231-798_#1
SU4_G1_223-806_#7
SU4_G1_223-806_#8
SU4_G1_223-806_SCR_#U
SU4_I1_225-806_#1
SU4_224-806_#4
SU4_221-806_65cm_#1
SU4_220-807_#1
SU4_221-806_#3
SU4_221-806_SCM_#2
SU4_221-807_#1
SU4_221-807_#2
SU4_221-807_#3
SU4_221-807_#4
SU4_221-807_#5
SU4_221-808_#1
SU4_222-806_@baulk221_#1
SU4_222-806_@baulk221_#2
SU4_223-806_#1
SU4_223-807_#U
SU4_224-806_#1
SU4_224-806_#2
SU4_224-806_#3
SU4_224-807_#1
SU4_G1_223-806_#1
SU4_G1_223-806_#2
SU4_G1_223-806_#3
SU4_G1_223-806_#4
SU4_G1_223-806_#4R
SU4_G1_223-806_#5
SU4_G1_223-806_#6
M1
M2
M3
M4
39
Phase
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern 1996
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Date
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 1996
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
Ambrose Lab ID
M5
M6
M7
M8
M9
M10
M11
M12
M13
M14
M15
M16
M17
M18
M19
M20
M21
M22
M23
M24
M25
M26
M27
M28
M29
M30
East1
East2
East3
East4
East5
East6
East7
East8
East9
East10
East11
East12
East13
East14
East15
West1
40
Phase
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Date
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
Ambrose Lab ID
West2
West3
West4
West5
West6
West7
West8
West9
West10
West11
West12
West13
West14
West15
Appendix B. Catalog of Shells used for Oxygen Isotope Data
Phase
Site Location
Date
Ambrose Lab ID
Iowa Lab ID
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
Phase 1
MU3 SU7
MU3 SU7
MU3 SU7
MU3 SU7
MU3 SU7
MU3 SU7
MU3 SU7
MU3 SU7
MU3 SU7
MU3 SU7
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
12th/early 13th Century
223/806, G1 #6
224/806, H1 #5
225/806, I1 #9
223/806, G1 #5
225/806, I1 #2
224/806, H1 #1
223/806, G1 #4
225/806, I1 #6
224/806, H1 #7
224/806, H1 #2
P1_1
P1_2
P1_3
P1_4
P1_5
P1_6
P1_7
P1_8
P1_9
P1_10
Phase 2
MU3
13th Century
224-806_Su6_H1_#2
P2_1
Phase 2
MU3
13th Century
225-806_SU6_I1_#4
P2_2
Phase 2
MU3
13th Century
P2_3
Phase 2
MU3
13th Century
224-806_SU6_H1_#3
223-806_SU6_#1
Phase 2
MU3
13th Century
P2_5
Phase 2
MU3
13th Century
224-806_SU6_H1_#5
224-806_SU6_H1_#1
Phase 2
Phase 2
MU3
MU4
13th Century
13th Century
223-806_SU5_G1_#1
Phase 2
MU3
13th Century
218-797_SU3_#1
223-806_SU5_G1_#2
P2_7
P2_8
Phase 2
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
House Tephra
MU3
H4, SU4
H4, SU4
H3, SU4
H3, SU4
H4, SU4
H4, SU4
13th Century
year 1362 AD
year 1362 AD
year 1362 AD
year 1362 AD
year 1362 AD
year 1362 AD
224-806_SU6_H1_#6
230-801, ex 3
230-801, ex 2
232-799, #6
232-799, #9
230-801, ex 1
230-801, #7
P2_4
P2_6
P2_9
P2_MU4
HT_1
HT_2
HT_3
HT_4
HT_5
HT_6
41
Phase
Site Location
Date
Ambrose Lab ID
Iowa Lab ID
House Tephra
House Tephra
House Tephra
House Tephra
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Phase 3/A
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
Modern
H3, SU4
H4, SU4
H3, SU4
H4, SU4
MU3 SU4
MU3 SU4
MU3 SU4
MU3 SU4
MU3 SU4
MU3 SU4
MU3 SU4
MU3 SU4
MU3 SU4
MU3 SU4
east side
east side
east side
east side
east side
west side
west side
west side
west side
west side
year 1362 AD
year 1362 AD
year 1362 AD
year 1362 AD
late 14th/15 Century
late 14th/15 Century
late 14th/15 Century
late 14th/15 Century
late 14th/15 Century
late 14th/15 Century
late 14th/15 Century
late 14th/15 Century
late 14th/15 Century
late 14th/15 Century
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
year 2011
231-799, ex 1
230-801, #6
231-799, ex 2
230-801, #5
223-807_G2_#1
224-806_#2
224-806_#4
220-807_#1
223-806_G1_#2
223-806_G1_#1
Baulk 221_222-806_#1
221-807_#2
224-806_#1
223-806_G1_#4
E11
E12
E13
E14
E15
W11
W12
W13
W14
W15
HT_7
HT_8
HT_9
HT_10
P3_1
P3_2
P3_3
P3_4
P3_5
P3_6
P3_7
P3_8
P3_9
P3_10
E_11
E_12
E_13
E_14
E_15
E_16
E_17
E_18
E_19
E_20
42