Modelling the influence of snow accumulation and snow-ice formation on theseasonal cycle of the Antarctic sea-ice cover

Recent observational and numerical studies of the maritime snow cover in th e Antarctic suggest that snow on top of sea ice plays a major role in shapi ng the seasonal growth and decay of the ice pack in the Southern Ocean. Her e, we make a quantitative assessment of the importance of snow accumulation in controlling the seasonal cycle of the ice cover with a coupled snow-sea -ice-upper-ocean model. The model takes into account snow and ice sublimati on and snow deposition by condensation. A parametrisation of the formation of snow ice (ice resulting from the freezing of a mixture of snow and seawa ter produced by flooding of the ice flees) is also included. Experiments on the sensitivity of the snow-sea-ice system to variations in the sublimatio n/condensation rate, the precipitation rate, and the amount of snowfall tra nsported by the wind into leads are discussed. Although we focus on the mod el response in the Southern Hemisphere, results for the Arctic are also dis cussed in some cases to highlight the relative importance of the processes under study in both hemispheres. It is found that the snow loss by sublimat ion can account for the removal of 0.45 m of snow per year in the Antarctic and that this loss significantly affects the total volume of snow ice. A p recipitation decrease of 50% is conducive to large reductions in the Antarc tic snow and snow-ice volumes, but it leads only to an 8% decrease in the a nnual mean ice volume. The Southern Ocean ice pack is more sensitive to inc reases in precipitation. For precipitation rates 1.5 times larger than the control ones, the annual mean snow, ice, and snow-ice volumes augment by 30 , 20, and 180%, respectively. It is also found that the transfer to the oce an of as much as 50% of the precipitating snow as a result of wind transpor t has almost negligible effects on the total ice volume. All the experiment s exhibit a marked geographical contrast in the ice-cover response, with a much larger sensitivity in the western sector of the Southern Ocean than in the eastern sector. Our results suggest that snow-related processes are of secondary importance for determining the sensitivity of the Arctic sea ice to environmental changes but that these processes could have an important part to play in the response of the Antarctic sea-ice cover to future, or c urrent, climatic changes.