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Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf, Antarctica

Ocean modellers at BAS have been studying the circulation in the Amundsen Sea, in order to understand what drives relatively warm Circumpolar Deep Water (CDW) onto the continental shelf. CDW is responsible for the high melt rates observed beneath the floating tongues of the major outlet glaciers that drain into Pine Island Bay. These glaciers have thinned and accelerated over the past decade and a half, and as a direct result are currently contributing 0.25mm/yr to global sea-level rise. One possibility is that these changes have been caused by a change in the delivery of CDW to the shelf.

In the model, the warmest CDW to reach Pine Island Bay was channelled through a submarine trough that extends from the glacier tongues to the edge of the continental shelf and that was carved out during previous advances of the ice sheet. This trough had already been identified as a site of CDW flow onto the shelf but nothing was known about the variability of the inflow over time. The implication of the model results is that the inflow is controlled by the regional wind forcing, and as a result is highly variable.

The winds over the Amundsen Sea are dictated by a low pressure region that migrates west towards the Ross Sea then back east towards the Bellingshausen Sea over the course of the year. This motion causes a change in the direction of the mean wind field over the outer continental shelf. Each year a period of westerly winds draws CDW onto the shelf, resupplying Pine Island Bay via the submarine trough.

These results are significant because they illustrate how rapidly atmospheric change can be transmitted to the ice sheet via the ocean. Previously it was assumed that the ice sheets were relatively immune to change via this route, because it will be centuries before any rise in surface air temperature can reach deep enough into the ocean to warm the CDW. But now our model suggests that any change in the atmosphere that affects the winds, such as changes in the Southern Annular Mode that might be linked directly to anthropogenic influences, could alter the delivery of ocean heat to Antarctica’s ice shelves and floating glacier tongues.

Find link to the full paper in the NERC Open Research Archive

Authors

Thoma, M., A. Jenkins, D. Holland, and S. Jacobs (2008)

Publication

Geophys. Res. Lett., 35, L18602, doi:10.1029/2008GL034939