Questo seminario è stato organizzato presso la sede CMCC/INGV di Bologna, via Franceschini 31 (Piano terra, Auditorium – ore 12.00).

Lecturer
Verena Haid, CMCC Foundation, Italy

Abstract
In a warming climate, observations indicate that the sea ice extent around Antarctica has increased over the last decades. Suggested explanations are a) the stabilizing effect of increased mass loss of the Antarctic ice sheet, which freshens the surface waters and reduces vertical heat transport in the ocean and  b) changes and shifts in the atmospheric circulation affecting the sea ice drift. 
We performed a sensitivity study with an eddy-permitting sea ice-ocean model to investigate the sea ice response to alterations of the freshwater addition and wind forcing.  A set of numerical simulations with variations in either amount and distribution of the prescribed surface freshwater flux or the strength of the horizontal wind components of the ERA-Interim forcing. Our results confirm that an increase in fresh water input can increase the sea ice extent. However, a very strong increase of freshwater will eventually invert the trend. The spatial distribution of the freshwater is of great influence. 
It affects sea ice dynamics and can strongly alter regional sea ice concentration and  thickness. Furthermore, additional coastal runoff generally leads to fresher and warmer dense shelf waters. We estimate that the current contribution by increased Antarctic runoff to the observed trend in the sea ice extent is about 15-50%. The influence of the wind on the sea ice is stronger in comparison. Increase of zonal wind speeds easily leads to deep convection in the Atlantic sector and a loss of sea ice area. An increase of southerly winds, causing more coastal polynyas and increased winter sea ice production, leads to thinner sea ice. But region-dependent strengthened southerly and northerly winds, lead to an increase in sea ice volume and extent, underlining the importance of the Amundsen Sea Low. Generally, stronger winds lead to a salinification of the coastal water column, but temperatures on the shelves may rise due to Ekman pumping.