THE ARCTIC-OCEAN NORDIC SEAS THERMOHALINE SYSTEM

The Arctic Mediterranean Sea is located north of the Greenland-Scotlan d Ridge and allows warm water from lower latitudes to penetrate beyond the Polar Circle. The northward flowing water is cooled in the Norweg ian Sea and its density increases. In the Arctic Ocean the high river runoff and the net precipitation lead to a density decrease in the sur face layers and heat loss at the sea surface results in the formation and maintenance of a permanent sea-ice cover. Brine ejected by freezin g creates dense waters on the Arctic Ocean shelves, which sink as conv ecting boundary plumes into the deeper layers. In the Eurasian Basin t he water column primarily reflects the interaction between the two inf lows from the Norwegian Sea: through Fram Strait and over the Barents and Kara Sea and their different transformation histories. In the Cana dian Basin the water transformations are dominated by the boundary con vection, which makes the Canadian Basin water column different from th at of the Eurasian Basin already at levels shallower than the now know n sill depth of the Lomonosov Ridge. In the Greenland Sea deep-reachin g, open-ocean convection occurs, partly rehomogenising the water colum n. The waters entering the Arctic Mediterranean are thus transformed p artly into a low salinity, cold upper layer, partly into cold, dense d eep waters which all re-cross the Greenland-Scotland Ridge. The dense waters sink into the deep North Atlantic to supply the North Atlantic Deep Water. A reduction of the deep convection in the Greenland Sea ha s recently been inferred and the Greenland Sea deep water renewal pres ently occurs by advection of deep waters from the Arctic Ocean. Observ ed changes in the temperature and salinity of the Greenland Sea Deep W ater are used to estimate the vertical diffusion coefficient in the de ep layers and the renewal time of the deep salinity maximum layer, whi ch originates from deep water outflow from the Eurasian Basin through Fram Strait. A weaker convection in the Greenland Sea is found to infl uence primarily the deep water circulation internal to the Arctic Medi terranean. The supply of dense overflow water from the upper layers in the Greenland Sea and from the other sources is not expected to be re duces. (C) 1997 International Council for the Exploration of the Sea.