Ice concentration in the Southern Ocean for the years 1978 to 1997, results from the PELICON Project

Sea ice is an integral part of the climate system of the high latitude regions. Up to now, control of its occurrence and extent, especially its interannual and long-term variability, has proved difficult to isolate or quantify, especially in the data devoid regions of the Southern Ocean. The consequences of climate change induced, for example, by the continued increase of greenhouse gases, on the occurrence of sea ice, is even less certain, although the theory at least suggests that sea ice extent changes could be expected to have a positive feedback role, i.e. that reduced ice extent could be expected to enhance warming at high latitudes. The interaction of sea ice with the polar ocean and atmosphere can be summerized as follows: - The snow covered sea ice reflects the solar illumination much stronger compared to open water areas. Therefore, changes in the horizontal coverage of sea ice (ice concentration) would be related to changes of the surface reflectivity. In the polar winter, sea ice isolates the ocean from the cold polar atmosphere and reduces the heat transfer by one or two orders. Both has a strong impact on the radiation balance. - Sea ice growth and melting has a signinficant influence on the circulation of the oceans. The formation of sea ice increases the water density of the ocean boundary layer due to rejection of brine. This results in an unstable stratification of the ocean layer and deep water formation can occure. The opposite behaviour can be observed when sea ice melts. The additional freshwater causes the ocean to form a stable boundary layer