Decadal sea-ice variability over the Weddell Sea in a coupled GCM

Yushi Morioka1, Liping Zhang2, Thomas L Delworth3 and Swadhin K Behera1, (1)JAMSTEC/APL, Yokohama, Japan, (2)NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, NJ, United States, (3)NOAA/GFDL, Princeton, NJ, United States
Weddell Sea, one of the Antarctic Seas, plays an important role in regulating long-term global climate through generation of the Antarctic Bottom Water. Sea-ice cover over the Weddell Sea significantly affects the water mass formation and circulation, but physical processes underlying low-frequency variability such as decadal sea-ice variability are not fully understood. Analysis of observational data and 300-yr simulation output using a coupled general circulation model (SINTEX-F2) reveals that decadal sea-ice variability over the Weddell Sea is strongly linked to zonal wind variability induced by remote forcings such as the Southern Annular Mode (SAM) and the Interdecadal Pacific Oscillation (IPO). It is found that remotely induced easterly wind anomalies over the Weddell Sea tend to suppress upwelling of subsurface warm water and lower sea-surface temperature (SST), leading to sea-ice increase. However, another 300-yr simulation output, in which the interannual sea-surface temperature outside the Weddell Sea and the South Atlantic is suppressed by nudging the model’s SST to monthly climatology, shows that local air-sea-ice interaction plays more active role in generating decadal sea-ice variability over the Weddell Sea. Enhanced evaporation associated with sea-ice decrease over the Weddell Sea is found to generate cyclonic atmospheric circulation anomalies while increasing near-surface salinity. This helps strengthen the Weddell gyre and enhance horizontal advection of cold water from the outside of the Weddell Sea, leading to sea-ice increase. These results suggest that local air-sea-ice interaction as well as remote forcing is important for generation of decadal sea-ice variability over the Weddell Sea.