DIATOM ASSEMBLAGES IN SURFACE SEDIMENTS OF THE ROSS SEA - RELATIONSHIP TO PRESENT OCEANOGRAPHIC CONDITIONS

Fifty four surface sediment samples from the western and central Ross Sea were examined to determine relationships between modem oceanograph ic conditions and surface sediment diatom assemblages. A centered R mo de principal components analysis demonstrates four geographically dist inct assemblages. The assemblage just north of the Ross Ice Shelf in t he central Ross Sea is most closely associated with Stephanopyxis spp. (a heavily silicified diatom abundant during the Pliocene), and may r esult from a combination of winnowing/reworking, and modern flux of pr imarily non-siliceous algae. The algal assemblage in the western part of the central Ross Sea is most closely associated with Thalassiosira gracilis (an open water diatom), and reflects early seasonal pack ice break up during the late spring inception of the Ross Sea polynya. The algal assemblage north of Drygalski Ice Tongue, in the western Ross S ea, is most closely associated with Fragilariopsis curta (a diatom com mon in stratified ice edge zones), suggesting that water column seedin g by species melting out of coastal sea ice is important in this area. The assemblage south of Drygalski Ice Tongue is most closely associat ed with resting spores of Thalassiosira antarctica (a diatom associate d with coastal waters). Although the habitat of T. antarctica requires future research, we speculate that sea ice conditions unique to area B support an autumnal T. antarctica bloom.