Abstract/Summary

In each of the last three decades of the 20th century there were unprecedented expansions of sea-ice over the Labrador Sea basin and influxes of cold fresh water into the subpolar gyre (SPG) which have been described as the Great Salinity Anomalies (GSAs). Employing data for sea surface temperature, salinity, and sea-ice cover, we propose that these events were downstream consequences of the expansion and subsequent melting of so-called “Odden” ice formed over the deep basin of the Greenland-Iceland-Norway (GIN) Sea in the 1960s, 1970s, and 1980s and additional to the normal East Greenland shelf sea-ice. We extend previous findings that Odden ice expansions were linked to winter episodes of high atmospheric pressure north of Greenland that directed freezing Arctic winds across the GIN Sea and may also have been associated with increased Arctic sea-ice volume leading to enhanced ice export through Fram Strait. We show that cold water and ice derived from Odden melting in the summer passed through Denmark Strait and along the East Greenland shelf, and accumulated in the Labrador Sea, creating favorable conditions for winter ice formation during particularly cold years in southwest Greenland. Meltwater from Odden and Labrador Sea ice appeared to break out into the SPG in the fall of 1982 and 1984 respectively and this cold water represents the likely source of the 1982–1985 GSA. These findings further our understanding of the physical processes linking ice formation and melt with ocean circulation in this key component of the climate system.