Constraints on ice volume changes of the West Antarctic Ice Sheet and Ross

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12th International Conference on Accelerator Mass Spectrometry (AMS-12)
the Last Glacial Maximum (~20 ka), marine evidence indicates that the grounding line of the West Antarctic Ice Sheet (WAIS) advanced northwards into the Ross Ice Shelf (RIS), blocking drainage of outlet glaciers through the Transantarctic Mountains (TM) resulting in significant downstream thickening of glacier profiles. The Darwin and Hatherton Glaciers in the TMs provide geological and pedological records of WAIS fluctuations that are interpreted as evidence for a LGM ice volume at least ~800 m thicker than today. Cosmogenic 10Be and 26Al exposure ages at Lake Wellman and Dubris Valley from ice-sheet contact (850 masl) to mountain peak (600 masl) show a WAIS Pleistocene ice thickness some 800 to 400 meters thicker than today. However a cluster of mid-altitude moraine boulders, previously taken to demarcate the LGM advance, have exposure ages ranging from 30 to 40 ka. This suggests that while WAIS expansion during the early Pleistocene was large, its LGM ice volume was not as large as previously estimated and little different from what is observed today (at most 50 m above current ice surface). A second site further north, Diamond Hill, lies at the confluence of the Darwin Glacier and RIS. Two transects were sampled on Diamond Hill that cover an altitude range of 1100 meters. Preliminary 10Be cosmogenic dates show a similar trend to that seen further up glacier in Lake Wellman. For the case of Diamond Hill, the WAIS was approximately 900 meters thicker than the current Rose Ice Shelf configuration at ~1.5Ma and with only minor advances in the last 10ka. As with Lake Wellman no evidence of large scale LGM advances were found. These results raise serious questions about the implications of a reduced West Antarctic ice Sheet at the LGM, and how the Antarctic ice sheets respond to global warming. Copyright (c) 2011 AMS12
Ice, Cosmology, Antarctica, Glaciers, Altitude, Greenhouse effect
Fink, D., Storey, B., Joy, K., Shulmeister, J., (2011). Constraints on ice volume changes of the West Antarctic Ice Sheet and Ross. 12th International Conference on Accelerator Mass Spectrometry (AMS 12), 20th - 25th March 2011. Museum of New Zealand: Te Papa Tongarewa, Wellington, New Zealand.