LATE WINTER MICROBIAL COMMUNITIES IN THE WESTERN WEDDELL SEA (ANTARCTICA)

Microbial communities in the water column and sea ice were studied during the EPOS-cruise on R/V Polarstern in the western Weddell Sea in late winter (October-November 1988). Samples were taken from four transects from heavy pack-ice to open water. The results indicated the important role of protozoans especially in the ice-edge area. Heterotrophic nanoflagellates, dinoflagellates, ciliates and sarcodines showed significant positive correlations with chlorophyll a. Autotrophic picoplankton and autotrophic flagellates, which were probably motile zooids of Phaeocystis pouchetii (up to 3 x 10(6) cells 1(-1)), were most abundant in the areas of low or medium chlorophyll a concentration. Sea ice contained high numbers of heterotrophic organisms, and the distribution of the different groups showed distinct vertical zonation. At two sites, the microbial assembly beneath the ice was clearly influenced by communities from the melting ice.