Magnitude and timing of orbitally paced Antarctic ice sheet variations through the Pliocene and Pleistocene
Abstract
A new 3-D ice sheet-shelf model, Global Climate Model (GCM) and nested Regional Climate Model (RCM) are applied to the Antarctic region, with simulations designed to span the full range of Pliocene to modern climatic forcing. The ice sheet model simulates a dynamic West Antarctic Ice Sheet (WAIS), with repeated, sudden retreats and readvances throughout the Pliocene and Pleistocene. Simulated WAIS variability in the Pliocene is dominated by 40-kyr cyclicity. Major WAIS collapses are less frequent in the Pleistocene, but do occur during a number of apparent “super-interglacials”, including MIS 31. WAIS is shown to be most sensitive to changes in sub-ice oceanic melt, however changes in East Antarctic Ice Sheet (EAIS) volume driven by this mechanism are shown to be limited. Maximum equivalent sea level rise simulated by the model is ~7 m, most of which is contributed by WAIS retreat. This is significantly less than the amount required to match estimates of sea level during the Pliocene (~25-40 m) and some Pleistocene interglacials (e.g., MIS 11; 20+ m), even with an additional contribution from Greenland (~7 m). We use a nested, high resolution GCM-RCM to test the potential for an additional contribution to sea level rise via surface melt on the EAIS, but find that the combined forcing from elevated Pliocene CO2 (400 ppmv), increased oceanic heat flux and reduced sea ice, warm austral summer orbits, and the loss of WAIS do not provide enough additive warming to produce significant summer ablation on the flanks or interior of the EAIS. This important model-data discrepancy implies either that the ice sheet model is lacking some critical underlying physical processes, the climate model is undersensitive to greenhouse gas forcing, or the sea level estimates during these periods are unrealistically high. We conclude by exploring the potential for more EAIS variability in the ice model by considering alternative treatments of both the conditions at the bed of the ice sheet and poorly constrained topographic boundary conditions - especially in potentially sensitive, low-lying regions of the EAIS margin which may have been prone to streaming and ice sheet drawdown.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP41D..02D
- Keywords:
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- 0726 CRYOSPHERE / Ice sheets;
- 1621 GLOBAL CHANGE / Cryospheric change;
- 3344 ATMOSPHERIC PROCESSES / Paleoclimatology;
- 3355 ATMOSPHERIC PROCESSES / Regional modeling