SPATIAL PATTERNS IN THE LENGTH OF THE SEA-ICE SEASON IN THE SOUTHERN-OCEAN, 1979-1986

The length of the sea ice season summarizes in one number the ice cove rage conditions for an individual location for an entire year. It beco mes a particularly valuable variable when mapped spatially over a larg e area and examined for regional and interannual differences, as is do ne here for the Southern Ocean over the years 1979-1986, using the sat ellite passive microwave data of the Nimbus 7 scanning multichannel mi crowave radiometer. Three prominent geographic anomalies in ice season lengths occur consistently in each year of the data set, countering t he general tendency toward shorter ice seasons from south to north: (1 ) In the Weddell Sea the tendency is toward shorter ice seasons from s outhwest to northeast, reflective of the cyclonic ice/atmosphere/ocean circulations in the Weddell Sea region. (2) Directly north of the Ros s Ice Shelf anomalously short ice seasons occur, lasting only 245-270 days, in contrast to the perennial ice coverage at comparable latitude s in the southern Bellingshausen and Amundsen Seas and in the western Weddell Sea. The short ice season off the Ross Ice Shelf reflects the consistently early opening of the ice cover each spring, under the inf luence of upwelling along the continental slope and shelf and atmosphe ric forcing from winds blowing off the Antarctic continent. (3) In the southern Amundsen Sea, anomalously short ice seasons occur adjacent t o the coast, owing to the frequent existence of coastal polynyas off t he many small ice shelves bordering the sea. Least squares trends in t he ice season lengths over the 1979-1986 period are highly coherent sp atially, with overall trends toward shorter ice seasons in the norther n Weddell and Bellingshausen seas and toward longer ice seasons in the Ross Sea, around much of East Antarctica, and in a portion of the sou th central Weddell Sea.