Rapid deglaciation of Marguerite Bay, western Antarctic Peninsula in the Early Holocene

Glacial geological evidence of rapid ice stream retreat is important for the potential insight it can bring to understanding of contemporary rapid ice sheet change. Here, we report new chronological constraints on the deglacial history of the Marguerite Trough Ice Stream, which formerly drained part of the western margin of the Antarctic Peninsula. This ice stream has been previously identified on geomorphological grounds as an example of an outlet that underwent rapid retreat following the Last Glacial Maximum, but the precise timing of this retreat has not been conclusively determined. We obtained cosmogenic surface exposure dates on erratic boulders that record the thinning history of ice flowing into the ice stream. These dates show that the ice stream underwent >270 m of thinning very rapidly at 9.6 ka BP. The timing of ice stream thinning agrees closely with previously published data on ice shelf retreat, the age of the first post-glacial beaches, and minimum constraining ages for the onset of lacustrine sedimentation, and post-glacial sedimentation in inner shelf fjords. We compare the timing of retreat to the similarly-sized Anvers Trough ice stream further north and find that retreat in Marguerite Bay was more rapid and earlier than in the Anvers Trough. We argue that the intrusion of Circumpolar Deep Water is the most likely forcing mechanism for retreat in Marguerite Bay. A key finding of this study is that rapid retreat occurred in deep water with reverse (continent-dipping) slope but also in relatively shallow water with a positive slope. This may have implications for understanding of oceanographically-forced ice sheet change in other parts of West Antarctica. (C) 2011 Elsevier Ltd. All rights reserved.

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