HYDROGRAPHY AND BIOCHEMICAL INDICATORS OF MICROPLANKTON BIOMASS IN THE BRANSFIELD STRAIT (ANTARCTICA) DURING JANUARY 1994

The relationships between hydrography and spatial distribution of seve ral biochemical indicators of microplankton biomass (chlorophyll, prot ein and ATP) were studied in an area covering the eastern part of the Bransfield Strait and the northern part of the Weddell Sea, during Ant arctic summer (January 1994). Four hydrographic zones were identified: (a) the northern part of the Bransfield Strait, covered by waters of Bellingshausen Sea origin; (b) a Weddell Sea water mass that affected most of the study area; (c) the Weddell-Scotia Confluence waters, obse rved north of Elephant Island; and(d) waters influenced by ice melting , found towards the southeastern part of the sampled area. The highest values of biomass indicators (chlorophyll a, ATP and protein) were fo und in the zones affected by ice-melting processes and in waters from the Bellingshausen Sea. The lowest Values of all biochemical parameter s were found in the Weddell Sea and in the Weddell-Scotia Confluence w aters. A high variability in the hydrographic structure and the distri bution of biochemical indicators was observed. The degree of stabiliza tion of the water column, the depth of the upper mixed layer and the g razing pressure of herbivorous zooplankton played a major role in the development, accumulation and spatial variability of microplankton bio mass.