Migration of Kuroshio Front and Paleoenvironment during the late Quaternary

通过微化石组合和有孔虫氧碳同位素测试，重建西北太平洋晚第四纪以来黑潮锋面迁移的古环境变化。4个海洋岩心分别采集于sugu湾、Bousou半岛和Kashima-NAda海域。对岩心进行了纳米浮游生物、硅藻、放射虫和有孔虫的微化石组合的详细分析，并对有孔虫的氧碳同位素进行了测试。结果表明，黑潮锋的波动情况如下：黑潮锋在公元前14000年到达骏河湾附近。在公元前1万2千到1万年之间，锋面撤退到苏格鲁湾的西南地区。在公元前1万年，锋面穿过了布苏半岛附近的地区。锋面在公元前7000年到5000年之间到达鹿岛附近。与现在相同的海洋学条件是在5000年b.p.p之后建立的。本研究还对从Bousou半岛日本海沟8800 m水深的沉积物捕集器样品中的硅藻和浮游有孔虫的分布进行了重要的基础研究。

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.