Limnology of Two Antarctic Epishelf Lakes and their Potential to Record Periods of Ice Shelf Loss |
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| Authors: | James A Smith Dominic A Hodgson Michael J Bentley Elie Verleyen Melanie J Leng Steven J Roberts |
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| Institution: | (1) British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, CB3 0ET Cambridge, UK;(2) Department of Geography, University of Durham, South Road, DH1 3LE Durham, UK;(3) Protistology and Aquatic Ecology, Ghent University, Krijgslaan 281 S8, B-9000 Gent, Belgium;(4) Natural Environment Research Council Isotope Geosciences Laboratory, British Geological Survey, Keyworth, NG12 5GG Nottingham, UK;(5) Institute of Geography, School of GeoSciences, University of Edinburgh, Drummond Street, EH8 9XP Edinburgh, UK |
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| Abstract: | George VI Ice Shelf is the largest ice shelf on the western side of the Antarctic Peninsula and its northern margin marks
the southern most latitudinal limit of recent ice shelf retreat. As part of a project to reconstruct the long-term (Holocene)
history of George VI Ice Shelf we studied two epishelf lakes impounded by the ice shelf at Ablation Point, on the east coast
of Alexander Island. These lakes, Moutonnée and Ablation, are stratified water bodies with a lower marine layer and an upper
freshwater layer. To determine if their sediment records could be used to detect past changes in the presence or absence of
the ice shelf it was necessary to describe their present-day limnology and sedimentology. We measured water column chemistry
and sampled the water column and sediments of the lakes along vertical and horizontal transects. We analysed these samples
for diatoms, stable isotopes (δ18O, δ2H, δ13CDIC, δ13Corg), geochemistry (TOC, TN, C/N ratios) and physical sedimentology (grain-size). This was supplemented by chemical and biological
reference data from the catchments. Results showed that the water columns of both lakes are nutrient limited and deficient
in phytoplankton. Benthic productivity is low and decreases with depth. Comparison of water column chemistry with an earlier
survey shows a net increase in the thickness of the freshwater layer in Moutonnée Lake between 1973 and 2001, which could
indicate that George VI Ice Shelf has thinned during this period. However, a similar trend was not observed in Ablation Lake
(5 km to the north) and an alternative explanation is that the changes are a seasonal phenomena. Data from the surface sediment
transects identified a number of proxies that respond to the present day stratification of the water column including diatom
species composition, stable isotopes and geochemistry, particularly in Moutonnée Lake. Collectively these data have been used
to develop a conceptual model for determining past ice shelf configuration in epishelf lakes. Specifically, periods of past
ice shelf loss, and the removal of the ice dam, would see the present stratified epishelf lake replaced by a marine embayment.
It is suggested that this change would leave a clear signature in the lake sediment record, notably the deposition of an exclusively
marine biological assemblage, increased ice rafted debris and δ13Corg values that are indicative of marine derived organic matter.
These authors contributed equally to this work |
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| Keywords: | Antarctic Limnology Diatoms Epishelf lakes Ice shelf collapse Isotopes Sediment traps |
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