THE THERMOHALINE CIRCULATION OF THE ARCTIC-OCEAN AND THE GREENLAND SEA

The thermohaline circulation of the Arctic Ocean and the Greenland Sea is conditioned by the harsh, high latitude climate and by bathymetry. Warm Atlantic water loses its heat and also becomes less saline by ad ded river run-off. In the Arctic Ocean, this leads to rapid cooling of the surface water and to ice formation. Brine, released by freezing, increases the density of the surface layer, but the ice cover also ins ulates the ocean and reduces heat loss. This limits density increase, and in the central Arctic Ocean a low salinity surface layer and a per manent ice cover are maintained. Only over the shallow shelves, where the entire water column is cooled to freezing, can dense water form an d accumulate to eventually sink down the continental slope into the de ep ocean. The part of the Atlantic water which enters the Arctic Ocean is thus separated into a low density surface layer and a denser, deep circulation. These two loops exit through Fram Strait. The waters are partly rehomogenized in the Greenland Sea. The main current is confin ed to the Greenland continental slope, but polar surface water and ice are injected into the central gyre and create a low density lid, allo wing for ice formation in winter. This leads to a density increase suf ficient to trigger convection, upwelling and subsequent ice melt. The convection maintains the weak stratification of the gyre and also rein forces the deep circulation loop. As the transformed waters return to the North Atlantic the low-salinity, upper water of the East Greenland Current enters the Labrador Sea and influences the formation of Labra dor Sea deep water. The dense loop passes through Denmark Strait and t he Faroe-Shetland Channel and sinks to contribute to the North Atlanti c deep water. Changes in the forcing conditions might alter the relati ve strength of the two loops. This could affect the oceanic thermohali ne circulation on a global scale