Abstract

The Antarctic shelf seas exhibit a strong bimodal distribution in the ocean temperature at the shelf seabed. The Amundsen and Bellingshausen (AB) shelf seas are flooded by relatively warm Circumpolar Deep Water, which is implicit in the recent ocean-driven erosion of the Antarctic Ice Sheet. In contrast, the Weddell and Ross shelf seas are filled with cold shelf waters, which cool and ventilate the deep ocean, and feed the global thermohaline circulation through Antarctic Bottom Water formation. Several mechanisms have been proposed to explain this distribution, such as the close proximity of the Antarctic Circumpolar Current to the AB shelf break. In our recent work, however, an idealised sea ice-mixed layer model was used to demonstrate that the bimodal distribution could be explained purely by regional differences in atmospheric forcing.

More recent investigations, using a sophisticated sea ice model (CICE) coupled to a simple mixed layer model, has demonstrated the dominant role of sea ice in controlling the mixed layer evolution within all four shelf seas. The model has also been used to understand the extent to which recent shelf sea trends (e.g. the Ross Sea freshening) can be explained directly by surface (e.g. sea ice) trends. The results add support to increasing ice shelf meltwater being the main cause of the recent freshening, however large uncertainties still remain.