Changes in marine-plankton diatom assemblages due to formation and development of Circum-Antarctic Current

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A time series of 65 sediment trap samples deployed in the western North Pacific Ocean, representing 48-month changes in diatom flora, seven DSDP (Deep Sea Drilling Program) cores from the Ocean, and 20 sea water and sea-ice samples from Lutzow-Holm Bay of Antarctica were analyzed.Temporal and spatial distribution of a single cosmopolitan diatom species, Thalassionema nitzschioides, and its varieties were found to be linked with the history of differentiation and distribution surface water masses due to changes in the ocean circulation system.In DSDP-ODP (Ocean Drilling Program) cores, T.nitzschioides is common in all late Paleogene to Quaternary sequences but not in cores from modern high-latitude Antarctic seas, over which Circum-Antarctic Current flows. Temporal variations of diatom abundance and species composition at Ocean Drilling Program Site 1095 cored on the continental rise along the Pacific side of Antarctic Peninsula were used to investigate the history of Polar Front migrations. The increases in abundance of T.nitzschioides at 5.7, 5.2-4.7 and 4.4-3.7 Ma, suggest a migration of Polar Front or Antarctic Convergence, a major boundary of plankton provinces in the modern Southern Ocean, to this site.These results suggest that temporal and spatial distribution of T.nitzschioides and its varieties is a new proxy for delineating the evolution of plankton provinces in relation to changes in distribution of surface water masses in the geologic past.