The thermohaline circulation of the Arctic Ocean and the Greenland Sea

Abstract

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 added 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 insulates the ocean and reduces heat loss. This limits density increase, and in the central Arctic Ocean a low salinity surface layer and a permanent ice cover are maintained. Only over the shallow shelves, where the entire water column is cooled to freezing, can dense water form and accumulate to eventually sink down the continental slope into the deep 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 confined to the Greenland continental slope, but polar surface water and ice are injected into the central gyre and create a low density lid, allowing for ice formation in winter. This leads to a density increase sufficient to trigger convection, upwelling and subsequent ice melt. The convection maintains the weak stratification of the gyre and also reinforces 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 Labrador Sea deep water. The dense loop passes through Denmark Strait and the Faroe-Shetland Channel and sinks to contribute to the North Atlantic deep water. Changes in the forcing conditions might alter the relative strength of the two loops. This could affect the oceanic thermohaline circulation on a global scale