HR: 1340h
AN: PP53B-01 INVITED    [Abstracts]
TI: Implications of contemporaneous observations of glacier changes on the sensitivity of ice sheets to climate change.
AU: * Rignot, E
EM: eric.rignot@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, ca 91109, United States
AB: Modern observations of ice sheet evolution, gathered mostly from satellites, have shed new lights on the sensitivity of glaciers and ice sheets to climate change. Widespread glacier acceleration observed along the southern coast of Greenland doubled the ice sheet mass deficit within a decade. The acceleration resulted from the thinning of the frontal regions by warm temperatures, which reduced buttressing and allowed faster rates of ice flow. Glaciers grounded well below sea level respond more dramatically to thinning as buoancy forces provide a positive feedback to the glacier retreat into deeper waters. Surface melt water and warmer ocean also play a direct role on the glacier evolution, but this is not fully understood at present. In the Antarctic Peninsula, there is widespread glacier acceleration on the west coast similar to that observed in Greenland. On the east coast, abrupt changes caused by ice-shelf collapses generated ten-fold increases in glacier flow which dwarf changes observed in Greenland. These changes in ice dynamics are not only significant in terms of mass balance, they dominate and make this region a contributor to sea level rise comparable to Alaska and Patagonia. Farther south, in the Bellingshausen and Amunden sea sectors, where climate warming is more subdued, there is widespread ice sheet imbalance concentrated along the narrow channels occupied by glaciers, hence also caused by ice dynamics. These glaciers are grounded well below sea level and prone to rapid retreat. Glacier thinning of many meters per year is common.Glacier and ice- shelf thinning in these regions are controlled by the thermal forcing from the ocean (ablation rates of ice shelves are orders of magnitude larger than surface mass balance) and the depth of the glaciers below sea level.Unfortunately, we lack of a lot of basic information on both. Yet, we know enough to recognize that numerical models of ice sheet flow that do not include glacier dynamics and ice shelf/ice stream interactions cannot explain any of the contemporaneous observations of glacier change. Over time scales of centuries, which are of interest to predict what ice sheets will do next, more sophisticated models that include glacier dynamics, thermal forcing from the ocean, and a detailed mapping of depths below sea level are essential. The International Polar Year will help make timely, major advances in this direction. This work was performed at Caltech's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration.
DE: 0720 Glaciers
DE: 0726 Ice sheets
DE: 0728 Ice shelves
DE: 0758 Remote sensing
DE: 0798 Modeling
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting