ABSTRACT

The West Antarctic Ice Sheet (WAIS) is losing volume at an increasing rate which is contributing to sea level rise. One proposed reason for the increased basal melt is a change in either the temperature or quantity of warm Circumpolar Deep Water (CDW) that moves onto the shelf and flows underneath the floating ice sheet. The WAIS rests largely on bedrock below sea level; so, as the ice melts, seawater can intrude under it causing it to float and exposing more ice to warm water. Calving of icebergs, runoff and basal melt due to oceanic water are the three major causes of volume loss for the WAIS. Basal melt is second in importance but the processes and driving mechanisms for the intrusion of oceanic water are not well understood. Possible dynamical processes are bottom Ekman layer transport, inertia-bathymetry interaction, Antarctic Circumpolar Current (ACC) density variation due to thermal wind, ACC dynamic instability, atmospheric forcing, and ice shelf circulation.

Intellectual Merit: The investigators propose to analyze the importance of each of these processes on cross shelf transport of CDW along the Antarctic continental shelf of the Amundsen and Bellingshausen Seas. The research hypothesis is that there is no direct or indirect effect of the atmosphere on oceanic processes that cause exchange of CDW along the shelf break of the Amundsen and Bellingshausen Seas. The alternative hypothesis is that the atmosphere has a dominant effect on oceanic processes that produce exchange of CDW along the shelf break of the Amundsen and Bellingshausen Seas. Process simulations will be conducted with an ocean-ice model (the Regional Ocean Modeling System with dynamic sea ice and ice shelves) that represents the character of the Amundsen and Bellingshausen shelves to test the influence of each process on shelf break exchange, transport across the shelf and basal melt of the ice shelf. Two realistic calculations will represent the Bellingshausen Sea and Amundsen Sea shelf area, respectively, forced by high resolution atmospheric forecasts and using boundary information from the large scale ocean models. Each models will have a 2 km (or smaller) grid spacing to properly represent baroclinic processes. Cross shelf transport of CDW and heat flux to the base of the ice shelf will be analyzed for each of these simulations. The relationship of these diagnostics to surface forcing and ACC speed as well as to atmospheric indexes (ENSO and SAM) will be determined.

Broader impacts: The climate of the Antarctic Peninsula and West Antarctica is changing rapidly. Furthermore, the WAIS is losing volume at an alarming rate, creating an urgent need to understand the processes by which warm oceanic water moves across the shelf under ice shelves and contributes to basal melting and, in some cases, to accelerate movement of the nearby ice sheets. This model study will identify processes affecting the intrusion of this oceanic water onto the shelf. It will also associate variability in the ACC in this region with climate indexes to project these results into the future to estimate the effect of oceanic changes on ice sheet movement and melting. A post-doctoral fellow will be train in ocean-ice modeling.

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