WEDDELL GYRE - STRUCTURE OF THE EASTERN BOUNDARY

In January-February 1988 a survey in the eastern part of the Weddell Gyre by three U.S.S.R. research vessels showed a complicated hydrographic structure that results from the intensive interaction between the waters of the Weddell Gyre and Antarctic Circumpolar Current. Three types of mesoscale features were found: warm-core eddies of circumpolar origin, with maximum temperature values in the range 1.7-2.1-degrees-C; warm-core eddies formed at the Weddell Front with maximum temperatures of 0.8-1.4-degrees-C; and cold-core features from the Cold Regime of the Weddell Gyre with a maximum deep water temperature of 0.7-degrees-C. The inflow of the Circumpolar Deep Water into the gyre is facilitated by the sharp southward excursion of the Antarctic Circumpolar Current core at about 26-degrees-E due to the topographical constraint of the mid-ocean ridge. Intense warm-core eddies forming at the Polar Front and drifting southward are visible in GEOSAT altimeter data as relatively high sea-level variability. The pure Cold Regime deep water with a maximum temperature <0.5-degrees-C occurs only in isolated patches west of 21-degrees-E.