Sea-ice anomalies observed in the Greenland and Labrador Seas during 1901-1984 and their relation to an interdecadal Arctic climate cycle

Two independent ice data sets from the Greenland and Labrador Seas have been analyzed for the purpose of characterizing interannual and decadal time scale sea-ice extent anomalies during this century. Sea-ice concentration data for the 1953-1984 period revealed the presence of a large positive anomaly in the Greenland Sea during the 1960s which coincided with the ``great salinity anomaly'', an upper-ocean low-salinity water mass that was observed to travel cyclonically around the northern North Atlantic during 1968-1982. This ice anomaly as well as several smaller ones propagated into the Labrador Sea and then across to the Labrador and east Newfoundland coast, over a period of 3 to 5 years. A complex empirical orthogonal function analysis of the same data also confirmed this propagation phenomenon. An inverse relation between sea-ice and salinity anomalies in the Greenland-Labrador Sea region was also generally found. An analysis of spring and summer ice-limit data obtained from Danish Meteorological Institute charts for the period 1901-1956 indicated the presence of heavy ice conditions (i.e., positive ice anomalies) in the Greenland Sea during 1902-1920 and in the late 1940s, and generally negative ice anomalies during the 1920s and 1930s. Only limited evidence of the propagation of Greenland Sea ice anomalies into the Labrador Sea was observed, however, probably because the data were from the ice-melt seasons. On the other hand, several large ice anomalies in the Greenland Sea occurred 2-3 years after large runoffs (in the early 1930s and the late 1940s) from northern Canada into the western Arctic Ocean. Similarly, a large runoff into the Arctic during 1964-1966 preceded the large Greenland Sea ice anomaly of the 1960s. These facts, together with recent evidence of `climatic jumps' in the Northern Hemisphere tropospheric circulation, suggest the existence of an interdecadal self-sustained climate cycle in the Arctic. In the Greenland Sea, this cycle is characterized by a state of large sea-ice extent overlying an upper layer of cool, relatively fresh water that does not convectively overturn, which alternates every 10-15 years with a state of small sea-ice extent and relatively warm saline surface water that frequently overturns.