CHEMOTAXONOMIC ANALYSIS OF PHYTOPLANKTON DISTRIBUTION IN THE INDIAN SECTOR OF THE SOUTHERN-OCEAN DURING LATE AUSTRAL SUMMER

An analysis of chlorophyll alpha and of taxon-specific pigments, as me asured by High Performance Liquid Chromatography (HPLC), revealed the abundance, composition and fate of phytoplankton in the Indian sector of the Southern Ocean, during the late austral summer of 1994 (ANTARES 2 cruise). In the study area (49 degrees S-67 degrees S, 62 degrees E ), four different sub-systems are presented from south to north: the C oastal and Continental Shelf Zone (CCSZ), the Seasonal Ice Zone (SIZ), including the Antarctic Divergence (AD), the Permanent Open Ocean Zon e (POOZ) and a frontal system, the Polar Frontal Zone (PFZ). The phyto plankton biomass was low everywhere, never exceeding 0.45 mg Chl alpha m(-3). The highest biomass was found in the CCSZ, in the AD and in th e PFZ. Diatoms were the dominant phytoplankton in the CCSZ, in the SIZ and in the AD; nanoflagellates dominated in the POOZ and in the PFZ. An analysis of physical and chemical factors indicated their influence on phytoplankton abundance, composition and fate. Thus, a high diatom biomass was found in areas where silicic acid was most abundant and w here the euphotic zone was deeper than the wind-mixed layer. According to the concentrations of chlorophyll alpha and its degradation produc ts (phaeopigments) in the water and in sediment traps (200 m), grazing pressure appeared to differ between south and north. The export rate was generally low, less than 0.3 % per day, and was maximum at the AD and in the CCSZ. A relationship appears to exist between the autotroph ic biomass structure and the resulting flux of particulate organic mat erial out of the photic zone, i.e. the diatom-dominated system (CCSZ a nd SIZ) exported more than the nanoflagellate-dominated system (PFZ).