Seasonality in the ocean-sea ice-atmosphere response to Southern Ocean freshwater input
Ariaan Purich
Antarctic ice sheets and shelves are melting, adding freshwater to the Southern Ocean and changing the ocean circulation. Coupled climate models do not represent ice sheets or shelves, neglecting important climate impacts. Using the Southern Ocean Freshwater Input from Antarctica (SOFIA) multimodel ensemble, we investigate the seasonality of the ocean-sea ice-atmosphere response to an idealised freshwater addition of 0.1 Sv around the Antarctic margins. Southern Ocean freshening is commonly associated with surface cooling, evident in all months but strongest in summer. Sea ice coverage increases accordingly, however the strongest sea ice increase is seen in winter. All models simulate consistently surface-intensified tropospheric cooling and lower-stratospheric warming south of 35˚S. Tropospheric cooling is largely attributed to sea ice expansion and hence albedo increase in winter. This cooling yields a downward displacement of the tropopause, reduced stratospheric water vapor content and ultimately induces warming around 200 hPa. Further, an enhanced southward eddy heat flux explains warming at 10-100 hPa during austral winter. Despite a temporally and spatially uniform prescribed freshwater flux in the SOFIA ensemble, seasonality in the SST response, sea ice cycle and atmospheric dynamics result in a distinct seasonal pattern in the response to freshwater input around the Antarctic margins.
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