Migration of Kuroshio Front and Paleoenvironment during the late Quaternary

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The objective of this study is to reconstruct the paleoenvironmental change of the northwestern Pacific Ocean since the late Quaternary in terms of the migration of the Kuroshio front which is discriminated by the microfossil assemblages and oxygen-carbon isotopes of foraminiferal test. Four marine cores were collected from off the Sugaru Bay, Bousou Peninsula, and Kashima-NAda. The detailed analyses of the cores were performed on microfossil assemblages of nannoplankton, diatoms, radiolarians, and foraminifera, as well as oxygen-carbon isotopes of foraminiferal tests. Consequently, it was revealed that the Kuroshio front had fluctuated as follows:1. The Kuroshio front reached near the region off the Suruga Bay at 14,000 years B.P.2. The front retreated to the southwestern region off the Sugaru Bay between 12,000 and 10,000 years B.P.3. The front passed through the region off the Bousou Peninsula at 10,000 years B.P.4. The front reached near the region off the Kashima-nada between 7,000 and 5,000 years B.P.5. The same oceanographic condition as the present one was established after 5,000 years B.P.In the present study, an important and fundamental study was also carried out concerning the distribution of diatoms and planktonic foraminifera in the sediment trap samples which was recovered from water depth of 8,800 m at the Japan Trench off the Bousou Peninsula.