Cosmogenic ¹⁰Be and ²⁶Al isotope evidence for the timing and pattern of deglaciation, southern Antarctic Peninsula

BENTLEY, M.J.¹, FOGWILL, C.J.², KUBIK, P.³, SUGDEN, D.E.^2
1Department of Geography, University of Durham, South Rd, Durham, DH1 3LE, UK
²Department of Geography, University of Edinburgh, Drummond St, Edinburgh, EH8 9XP, UK
³Paul Scherrer Institut, c/o Institute of Particle Physics, HPK H30 ETH, Hoenggerberg CH-8093, Zurich, Switzerland

Contact e-mail: m.j.bentley@durham.ac.uk

We report here a framework chronology for deglaciation of the southern Antarctic Peninsula, following the Last Glacial Maximum (LGM). The chronology has been derived from ¹⁰Be and ²⁶Al cosmogenic exposure ages on erratic boulders in the southern Antarctic Peninsula. We have derived ages from both east (Weddell Sea) and west (George VI Sound) sides of the Peninsula The key features of the chronology are:

· The onset of deglaciation of the George VI Sound area was c. 18.3 ka. This was relatively early, compared to other areas of the West Antarctic Ice Sheet, and suggests a rapid response to sea level rise following the LGM.
· The east coast of Alexander Island was still covered by more extensive ice up until c. 7.3 ka
· Deglaciation of George VI Sound was a two-step process; the first step at 18.3 ka, and the second at c. 7.3 ka. At present, we have two hypotheses as to how this may have occurred. The first suggests that there was a two-step decline of the George VI Sound outlet glacier, whilst the second suggests a one-step decline of the GVIS outlet followed by local ice advance and subsequent retreat over Alexander Island, perhaps related to increased moisture supply after the LGM.
· The high eastern flank of the Peninsula ice sheet, close to the ice divide, was thinning by c. 11.8 ka
· There are numerous reworked boulders scattered across nunataks in the southern Antarctic Peninsula. Some of these may date back several glacial cycles.

These data carry a number of implications and can be compared to existing (mainly marine) chronological data.