Miocene paleoceanography around the North Pacific based on the activities of past primary producers and benthic organisms

对分布在日本太平洋一侧的新近纪和第四纪剖面的微体化石和遗迹化石以及相关的深海岩心沉积物进行了定性分析，以确定北太平洋表层环流系统的变化和深海环境的变化，以及对气候变化的意义。在长石地区发现了两个具有特征的超微化石和硅藻分类群，这使我们能够监测西北太平洋周围海洋锋面的运动。植物区系的变化可能与北太平洋环流的变化密切相关。例如，在大约0.85 Ma时，西北太平洋的一种凉爽而富含营养的表层洋流--大洋流--突然侵入日本岛屿周围的太平洋一侧。Oyashio流强烈侵入的时间恰好与中更新世过渡的初始事件(MPT；0.90~0.60 Ma)相吻合，对应于晚更新世向高频冰量波动的过渡时间(如Raymo，1990)。这意味着西北太平洋海洋锋面系统受全球气候变化的控制，气候变化发生在中更新世中期的高纬度地区。同时，底栖生物的活动和钙质凝固层的发育变得更加强烈，这表明北太平洋副热带环流发生了变化，深海环流也发生了变化。在中新世，也发现了同样的现象，因此，初级生产者的通量变化影响了海洋气候变化。

The qualitative analyses of microfossils and trace fossils from the Neogene and the Quaternary sections distributed in the Pacific side of Japan and related deep sea core sediments were performed to determine changes in surface circulation systems in the North Pacific and changes of deep sea environments, and implications for climatic changes. Stratigraphic occurrences of two characteristic taxa of nannofossils and diatoms in the Choshi area allow us to monitor the movement of the oceanographic front around the NW Pacific. Floral changes can be strongly related to the circulation changes around the North Pacific Ocean. For example, at approximately 0.85 Ma, the Oyashio Current, a cool and nutrient-rich surface current in the NW Pacific, suddenly invaded into the Pacific side around the Japanese islands. The timing of this strong invasion of the Oyashio Current coincides with the initial event of the mid-Pleistocene Transition (MPT;0.90〜0.60Ma), corresponding to the transition time to high frequnecy ice volume fluctuation during the late Pleistocene (e.g.Raymo,1990). This means that the oceanographic frontal system along the NW Pacific has been controlled by global climate change occurred in the high latitude during the middle Pleistocene. At the same time, activities of benthic organisms and developments of calcareous concretion layers had become stronger and thus, these results suggest that the subtropical gyre circulation in the North Pacific region had changed and deep sea circulations also altered. During the Miocene, same phenomena were also found and thus, flux changes of primary producers affected ocean climatic changes.