Freshwater Fluxes East of Greenland

The northern North Atlantic features areas of strong surface cooling which sets up a southward flow of sinking cold, dense waters in the deep ocean. A northward flow of warm surface waters replaces the sinking southbound waters; a loop often termed the meridional overturning circulation (MOC). The associated northward heat transport is an important moderator of the high latitude climate along the flow. It is a major concern that excessive amounts of freshwater added to the northern North Atlantic could alter the dense water formation and associated ocean density contrasts driving this part of the MOC (Häkkinen 1999; Haak et al. 2003). The region has been undergoing a remarkable freshening since the mid-1960s (Curry and Mauritzen 2005; Curry et al. 2003; Dickson et al. 2002). Sources of freshwater input are runoff from Greenland, net precipitation, and export of freshwater from the Arctic in the form of sea ice and melt water through Fram Strait and the Canadian Archipelago. In the late 1960s a major freshening event contributed with as much as half of the extra freshwater required to account for the observed 1965–1995 freshening (Curry and Mauritzen 2005). The event was labeled the Great Salinity Anomaly (GSA) (Dickson et al. 1988), and appeared as extraordinarily fresh water circulating in the Subpolar gyre during the 1970s. The freshwater release has been attributed to an anomalous export of sea ice through Fram Strait during the late 1960s (Häkkinen 1993; Karcher et al. 2005). Pulses of excess freshwater and sea ice appear to have been emitted from the Arctic also after the GSA; both the 1980s and 1990s featured appearances of low salinity water in the Subpolar gyre (Belkin 2004). Karcher et al. (2005) attributed the salinity anomaly of the 1990s to a large release of liquid freshwater from the Arctic through Fram Strait.