Sea ice variability and trends in the Weddell Sea for 1979-2006

Sea ice concentration in the Weddell Sea is subject to regional climate variability. The magnitude and origin of local trends in the sea ice coverage were studied using the bootstrap algorithm sea ice concentration data from the NSIDC for 1979-2006. The impact of atmospheric forcing such as air temperature, wind speed, and cloud coverage, gained from NCEP/NCAR reanalysis, on sea ice was assessed by analyzing correlation coefficients between the respective atmospheric component and the satellite-observed sea ice concentrations. It was found that sea ice concentrations increased in the eastern and decreased in the western Weddell Sea, predominantly in the marginal sea ice zone. There, and in coastal regions, temperature variability is strongly anti-correlated to the variability of sea ice concentration. In the central Weddell Sea, warmer air masses and the redistribution of sea ice, induced by an observed shift of the prevailing westerly winds towards the south, are suggested as reasons for the positive correlation between air temperatures and sea ice concentration in this region. Sea ice concentration trends are well connected to trends in the air temperature and wind fields, but sea ice drift trends, analyzed using the Polar Pathfinder sea ice motion vectors, differ from those in the wind field. These differences are to some extent interpretable when considering sea ice deformation changes. \nModelling the state and trends of the sea ice cover with the Finite Element Sea ice - Ocean Model (FESOM) showed that sea ice thicknesses predominantly indicate the same tendencies as the simulated sea ice concentrations, which results in an increase of the total sea ice volume by 1 % per decade in the Weddell Sea.