Recent Advances in the Analysis of SAR Data of the Polar Oceans

Abstract

Studies of the behavior of the world’s sea ice cover are particularly important because sea ice, with its associated snow cover, serves as an insulative layer separating the frigid Arctic atmosphere from the relatively warm underlying ocean. In fact, the heat fluxes through typical thick multiyear ice are two orders of magnitude less than fluxes observed under equivalent meteorological conditions through newly formed ice leads. Even though the areal coverage by thin ice is small (several percent) in the Arctic, the integrated flux through this area would be comparable to that through thicker ice. The presence of sea ice cover also changes the surface albedo from a value of 0.15 (for open water) to 0.84 (dry snow on the surface of sea ice). Therefore, decreases in sea ice extent and thickness caused by climatic warming would result in a pronounced positive feedback amplifying the observed change. A warming trend would be expected to result in a decrease in the extent and thickness of sea ice, in turn causing further atmospheric and oceanic warming and thus contributing to even further decreases. It is this sea ice feedback that contributes to the increases in mean annual temperatures that have been projected in simulations changes in global climate (Manabe and Stouffer 1980). In the Greenland Sea, where Arctic sea ice exported through the Fram Strait encounters the warmer North Atlantic water, there is net ice melt. It appears that deep convection - the mixing of surface water with deep ocean water - in the Greenland and Iceland Seas is conditioned by freshwater export from the Arctic Ocean. This melt process may be important in maintaining the stratification of the ocean in this area, thus preventing significant overturning (Aagaard and Carmack 1994). It was hypothesized that at some level of increased export of ice, convection would cease; the northward transport of Atlantic water would decrease; and the climatological ice cover would spread southward. Conversely, if the export were to decrease, a northward movement of the ice cover would be expected due to a weakening of the stratification in the Eurasian Basin.