Classification of water masses in the area investigated during the 1981 FIBEX Expedition and two winter expeditions at the "H. Arctowski" Station using the method of Empirical Orthogonal Functions (EOF) is presented. Four basic water masses (warm and cold Bellinghausen Sea surface waters, surface Weddell Sea waters, Circumpolar Warm Deep Water (CWDW) and the transitional zone) were observed in the area and a significant dependence of water masses distribution ón depth was found. A strong winter increase in the Weddell Sea waters influence was recorded.
On the basis of T/S measurements water masses were differentiated and geostrophic currents were drawn. It was stated, that the Weddell Sea waters filled a major part of Bransfield Strait from the southeast to Trinity Island on the west. Waters originating from Bellingshausen Sea occurred in the western and northern part of the research area and along the southern coasts of Shetlands. The direction of the geostrophic current is from the southwest to the northeast with a branch in the south at the top of the Antarctic Peninsula.
Net of temperature, salinity and dissolved oxygen content measurements were made in situ at 24 stations in Admiralty Bay with the use of automatic analyzer Martek MK IV. Results proved a presence of two water masses located horizontally one over the other, with the boundary at depth of 15—35 m. The main, lower mass consists of homogenous waters inflowing from the Bransfield Strait. The upper, thin and much differentiated layer is formed through interaction of the main underlying water mass with meltwaters from glaciers and sea ice. It is probably formed along the whole archipelago and carried by surface currents into the bay where it is subjected to further modifications. Local salinity and temperature extremes are associated with glacier water runoff; local dissolved oxygen maxima seem to be connected with phytoplankton distribution. Strong currents occurring in te bay due to water circulation may cause local, short term and sometimes considerable fluctuations in values of parameters recorded at individual stations.
Four water masses were distinguished in the upper water layer between Elephant Island and the South Orkneys. Measurements of temperature, salinity, concentrations of dissolved oxygen and silicates were used for the analysis of the hydrological situation and to recognise the origin of water masses. For additional information, nitrates and chlorophyll concentrations were used. Drake Passage and Bransfield Strait waters occupied the western part of the investigated area, from surface to 150 m depth. Below, the Circumpolar Warm Deep Waters (CWDW) were found. The region east of 53.5°W was occupied by winter Weddell Sea water. Above this, a 45 m thin layer of summer modification of Weddell Sea Surface Water was found between 49°W and the South Orkneys. The highestchlorophyll α concentrations were found in this modified water.