THE KUROSHIO MOVEMENT AND OCEANIC ENVIRONMENTAL CHANGE FOR THE LAST 150,000 YEARS

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In order to reconstruct the paleoenvironmental changes related to the Kuroshio movement around the Japanese Islands since the last 150,000 years, we have carried out multidisciplinary analysis on about 15 marine sediment cores collected from the surrounding sea areas of Japan. The new results obtained are summarized as follows : 1) From the relative abundance of warm-water planktonic foraminifera in a core off Sanriku district, it has been inferred that the effect of the Kuroshio Current was strong during the oxygen isotopic stages 5._1 and 1, nearly absent during the stages 4 and 2, and sometime observed during the stage 3.2) From faunal and oxygen isotopic analysis of planktonic foraminifera in a core off Kashimanada, it has been revealed that the sea surface temperature(SST)decreased by several to nearly ten degrees Celsius at the last glacial maximum. 3) Compared to the Holocene SST,a decrease of 2-3ﾟC in SST during the last glacial period is revealed by the UK37-index analyzes in several cores off the southern coast of Japan. The accumulation rates of eolian dust (Quartz, Feldspar, Illite), as well as organic carbon content, increased during the last glacial period than in the Holocene. 4) Nannofossil assemblage in one of the southernmost core (30ﾟN) off the southern coast of Japan show fluctuations in accordance with the global climatic change since the last 130,000 years. The biological productivity in this core site, however, does not change so much. This suggests that the influence of the Kuroshio Current did not reach as far north as 30ﾟN during the last 130,000 years. 5) In a core from the Okinawa Trough, the organic carbon and nitrogen isotopic ratios has remained relatively constant since the last 40,000 years. This suggests that the Kuroshio Current has been convected into the Okinawa Trough for the last 40,000 years.