An analysis of the atmospheric processes driving the large-scale winter sea ice variability in the Southern Ocean

The response of the sea ice in the Southern Ocean to the variability of the atmosphere on the period 1979-2004 is investigated using both model and observational data. On the one hand, our results show that in line with previous investigations, the classical modes of atmospheric variability do not explain a large part of the winter sea ice extent variability integrated over the entire Southern Ocean. On the other hand, the regression between the ice extent and the atmospheric pressure displays a pattern with low pressure areas over the South Atlantic, over the Indian Ocean, and on the southwestern part of the Pacific Ocean and a high pressure area over the Antarctic region extending toward both the southeastern Pacific and the region south of Australia. This pattern, which does not correlate significantly with any of the known modes of atmospheric variability, induces changes in the sea ice extent by influencing the air temperature, the ice production, and both the meridional and the zonal ice velocity. However, there is no clear link between the different centers of action of this pattern. Furthermore, the correlation of the sea ice extent between the different sectors is generally low. As a conclusion, we must consider that the sea ice extent in the Southern Ocean over the last 30 years does not behave as a single entity: Its variability is the result of the combination of regional sea ice changes. Each sector should thus be examined separately.