Reconstruction of Quaternary paleoenvironment in the Indian and Western Pacific Oceans based upon floral analysis of calcareous nannofossils.

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Calcareous nannoflora in four cores, three from the tropical to temperate regions of the eastern Indian Ocean and one from off-coast of SE Australia, were analyzed to reconstruct Quaternary paleoceanographic history of the Indian and Western Pacific Oceans. Followings are the major results of this investigation.1) Relative abundances of three lower-photic taxa fluctuated synchronously, thus the stratigraphic change in Florisphaera profunda, which is generally the only species preserved in deep sea sediment, was proven to be an accurate indicator of the strata stability in euphotic water.2) The percentage abundance of F.profunda indicates a ca. 100 kyr cyclicity of the monsoonal strength corresponding to the orbital eccentricity, and the significant reduction in F.profunda abundance indicates significant weakening of the monsoon during the interglacial periods.3) Influence of the Leeuwin Current lessened greatly during the glacial periods, and the reduction in F.profunda abundance in two mid-latitude cores taken from off-coast of the western Australia indicates a lower lower-photic temperature which was resulted by an increased influence of the Western Australian Current.4) The Leeuwin Current flows continuously at the northern margin of the Southern Ocean for the last 14 kyr, and the complete disappearance of tropical taxa confirmed the disappearance of the current during the past glacial periods.