The influence of Antarctic ice sheet topography change on Antarctic climate -- a positive feedback.

Abstract:

The potential for climate change to result in changes to the Antarctic ice sheet -- including the possibility of a full collapse of the West Antarctic Ice Shet (WAIS) is well known. Less well known is that the collapse of the ice sheet, if it occured, would have significant impcts on regional climate. We use climate model simulations to quantify the impact of topographic changes on the surface climate of Antarctica. As a general rule, lowered topography produces anomalous cyclonic circulation owing to fundamental atmospheric dynamical constraints. In the case of WAIS collapse, this causes increased flow of warm, maritime air toward the South Pole and cold-air advection from the East Antarctic plateau toward the Ross Sea and Marie Byrd Land, West Antarctica. This resulting pattern The result is cooling in some areas and warming in others, a pattern that is similar to that observed from ice core paleotemperature data for the last interglacial period, suggesting that WAIS collapse occurred at that time. We find that magnitude of the response is roughly linear with the magnitude of the imposed elevation change. The regional response over West Antarctica is large enough that it probably needs to be taken into account in modeling future changes to the ice sheet. Of particular interest is that lowering of the WAIS topography results in anomalous westerlies along the Amundsen Sea coastline. Anomalous westerlies in this region today are in large part responsible for the for intrusion of circumpolar deepwater onto the continental shelf, and the observed rapid thinning of West Antarctic ice shelves. A positive feedback may thus exist in which lowering of the WAIS surface from climate forcing may enhance that forcing, leading to further elevation lowering and ice sheet mass loss.