Late Quaternary relative sea level change in the South Shetland Islands, Antarctica

Abstract

Models have been inconsistent in their prediction of ice sheet volumes and extent over the Antarctic Peninsula and sub-Antarctic islands during the Last Glacial Maximum (LGM), and their contribution to sea level rise during subsequent deglaciation remains uncertain. The use of precise relative sea level (RSL) data offers great potential for inferring regional ice sheet histories, as well as helping to validate numerical models predicting future ice sheet evolution and RSL change. This thesis aims to elucidate the RSL history of the South Shetland Islands (SSIs), a sub-Antarctic archipelago peripheral to the northern Antarctic Peninsula ice sheet, by integrating evidence from isolation basins with geomorphological evidence from raised beaches. This will extend the only previously reported RSL curve from the area (Bentley et al., 2005a), which reveals a complex but poorly chronologically constrained RSL history. In addition, this work also aims to improve the understanding of the long-term tectonic influence on RSL change.

Sediment cores were taken from five lakes on Fildes Peninsula, King George Island (eastern SSIs) at a range of altitudes above present sea level. Diatom, stable isotope (δ13C) and physical analyses of sediments revealed clear marine-lacustrine transitions in lakes below 16 m above mean sea level (amsl), with no marine signal above this altitude. Together with radiocarbon dates from raised beaches, a RSL curve was produced for the last 9500 14C yr BP. This curve shows a mid-Holocene RSL highstand at 15.5 m amsl between ca. 6150 and 6700 14C yr BP, preceded by a period of extremely rapid RSL rise and followed by more gradual RSL fall as a consequence of isostatic uplift in response to regional deglaciation.

In addition, regional GPS surveys of raised beaches were conducted to assess the spatial pattern of glacio-isostatic rebound following deglaciation. The centre of uplift was found to closely coincide with the centre of the LGM ice sheet reconstructed by John and Sugden (1971). Beaches were modelled using polynomial trend surface analysis to constrain the spatial variability of isostatic uplift across the SSIs, which has enabled the regional extrapolation of the RSL curve across the archipelago. Finally, two independent approaches were taken to constrain the long-term tectonic uplift rate of the SSIs as 0.22-0.48 m/ka. Tectonic uplift contributes between 1.4 and 2.9 m to the reconstructed RSL highstand.