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Geomorphological evidence and cosmogenic ¹⁰Be/²⁶Al exposure ages for the Last Glacial Maximum and deglaciation of the Antarctic Peninsula Ice Sheet

Michael J. Bentley^,1, Christopher J. Fogwill^,2, Peter W. Kubik^,3 and David E. Sugden^#,4

¹ Department of Geography, University of Durham, South Road, Durham DH1 3LE, UK
² Institute of Geography, School of Geosciences, University of Edinburgh, Drummond Street, Edinburgh EH8 9XP, UK
³ Paul Scherrer Institut, c/o Institute of Particle Physics, ETH Zürich, 8093 Zürich, Switzerland
⁴ School of Geosciences, University of Edinburgh, Grant Institute, Kings Buildings, West Mains Road, Edinburgh EH9 3JW, UK

This paper presents the first systematic attempt to map the Last Glacial Maximum (LGM) configuration of the southern and central parts of the Antarctic Peninsula Ice Sheet, and to determine the timing of onshore ice-sheet retreat. Geomorphologic evidence shows that the LGM ice sheet expanded to form two ice domes in Palmer Land and merged with an expanded and thicker West Antarctic Ice Sheet in the Weddell Sea. Ice from the Antarctic Peninsula merged with Alexander Island ice in George VI Sound. Cosmogenic ¹⁰Be and ²⁶Al data from 29 erratics on nunataks yield model ages between 7.2 ka and older than 1 Ma. The data set contains a high proportion of erratics with evidence of nuclide inheritance. Once these ages have been excluded, the cosmogenic ages suggest that thinning of the west side of the Antarctic Peninsula Ice Sheet to near-present configuration was almost complete by the early Holocene. These data, combined with previously published ¹⁴C data, exclude the possibility that the west side of the Antarctic Peninsula Ice Sheet has been thinning throughout the Holocene, as has been demonstrated for some other sectors of the West Antarctic Ice Sheet. On the east side of the Antarctic Peninsula, ice-sheet thinning was under way prior to the early Holocene, but our data do not constrain the ice-sheet behavior more recently than 7.2 ka.

Key Words: glacial geology • Antarctic Peninsula • ice sheets • deglaciation • cosmogenic isotopes

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