On the Representation of Antarctic Sea Ice in a Global Ocean GCM

A realistic representation of Antarctic sea ice in global ocean and climate models is a challenging task, because Antarctic sea ice constitutes mainly thin first-year ice in a mostly marginally stably stratified ocean environment. It has been shown that the Antarctic sea-ice concentration and extent can be simulated rather realistically in a configuration with a hybrid high-resolution (20 km) sea-ice - coarse-resolution (200 km) ocean model where the upper ocean temperature is constrained by satellite-derived ice concentration (Stössel, 2008). However, the ice-thickness distribution in those simulations remained rather poor. It will be shown that the simulated ice-thickness distribution can be improved considerably in a model configuration that allows also for the ocean component to be presented at high resolution (20 km). It turns out that the main reason for the improvement is not the more detailed representation of the Antarctic coastline, the bathymetry, or the ice-shelf cavities, but rather the more detailed representation of the ocean currents. This leads to more spatial and temporal variability, affecting sea-ice convergence, and thus ridging, resulting in a change of the large-scale ice-thickness distribution. This and the former results indicate that the ocean is the most crucial component of the Antarctic atmosphere - sea-ice - ocean system in need of further understanding and improvements for realistic Antarctic sea-ice simulations (with all its consequences for the long-term global overturning circulation) to be achieved.