Physical Processes determining the Antarctic Sea Ice Environment

Abstract

The Antarctic sea ice zone undergoes one of the greatest seasonal surface changes on Earth, with an annual change in extent of around 15 × 10 6 km 2 . This ice, and its associated snow cover, plays a number of important roles in the ocean-atmosphere climate system: the high albedo ice cover restricts surface absorption of solar radiation and acts as a barrier to the exchange of mass and energy between the ocean and atmosphere, and salt rejected by the growing ice cover affects the ocean structure and circulation. Additionally, a number of sea ice feedback processes have the potential to play an important role in climate change. The extent to which a sea ice cover modifies ocean-atmosphere interaction is primarily determined by the thickness and concentration of the ice, but these themselves are determined by ocean and atmospheric interaction. The thickness distribution of the pack is determined by both thermodynamic and dynamic processes: most important at the geophysical scale are the dynamic processes of ice drift and deformation, and of lead formation. Compared to the ice cover in the central Arctic Basin, the Antarctic sea ice is highly mobile. Drifting buoy studies show that the Antarctic pack can move at speeds of up to 60 km per day or greater, and that around most of the Antarctic coast, the drift of the pack ice is generally divergent, with divergence rates of 10% or more per day being observed under some circumstances. Consequently there is generally some open water within the Antarctic pack and much of the total ice mass forms by rapid growth within these areas. This influences the crystal structure of the ice and results in a considerable portion of the Antarctic pack (up to 25% in spring-time) having a thickness of less than 0 · 3 m. In general much of the Antarctic sea ice only grows thermodynamically to about 0·5 m thick, with thickness increases beyond that resulting from the deformational processes of rafting and ridge-building.