Seasonal transitions and water mass formation in the Iceland and Greenland seas

Abstract

The dense waters of the Iceland and Greenland sea gyres are not simply the product of a gradual transition between cold, relatively fresh polar waters on the west and warmer, saline Atlantic water on the east, but instead constitute a unique hydrographic region, bounded by the polar and arctic fronts, which we term the arctic domain. Although deep and bottom water is the best-known water mass formed in the arctic domain, the region also produces a spectrum of dense intermediate water types in winter. Our study concentrates upon water mass formation in the Iceland Sea, where the principal winter product is an intermediate water mass nearly as cold as the deep water, but slightly less saline and therefore always lying above the deep water. The intermediate water mass produced in greatest volume in the Greenland Sea is warmer and more saline, although of nearly the same density as that produced in the Iceland Sea. The principal difference between the seasonal transitions in the Greenland and Iceland seas is that the transition in the Greenland Sea involves slightly more saline water than does that in the Iceland Sea, due to a more pronounced contribution of cooled Atlantic water. Subsequent along-isopycnal mixing of the intermediate water masses produces water which needs only to undergo a final cooling stage to be transformed into new deep and bottom water.