Surface-water evolution of the eastern East China Sea during the last 36,000 years

Planktic foraminifera have been studied in two high-resolution cores raised from the continental slope of the eastern East China Sea (ECS) to reconstruct the surface-water history. AMS C-14 dating on fifteen horizons revealed that the two cores KH82-4-14 and RN80-PC3 contain continuous records of the last 36 and 17 thousand cal. years, respectively. Thirty-one planktic foraminiferal species which are commonly found in the present western North Pacific and the ECS are recognized in down-core samples. Three faunal phases (III, II and I) distinguished by characteristic planktic foraminiferal assemblages suggest three major paleoenvironmental stages of the surface water of the eastern ECS since 36,000 yr B.P.: (1) a stage influenced by coastal water from 36,000 to 19,500 yr B.P.; (2) a stage also influenced by coastal water and extremely low salinity from 19,500 to 10,500 yr B.P.; and (3) a stage controlled by the modem open-sea water related to the Kuroshio with both higher temperature and higher salinity since 10.5-8.5 thousand years B.P. Oxygen isotope records of the planktic foraminiferal species G. bulloides show that the three planktic foraminiferal faunal phases correspond to the last glacial, deglacial and postglacial stages, respectively. The planktic foraminiferal assemblage during the deglacial stage which is represented by high percentages of G. quinqueloba, is quite different from those during the glacial and postglacial stages, linked to a large amount of river discharge from the Chinese continent. A negative oxygen isotope excursion in G. bulloides during the same period is highly correlated to the 'G. quinqueloba anomaly', also indicating a decrease in surface-water salinity. Furthermore, the sedimentation rate of core KH82-4-14 during 19-15 thousand years B.P. is much higher than the rates during the glacial and postglacial stages, suggesting a great increase in the supply of terrigenous material, related to an increased river and sediment discharge during the early deglaciation. The coastal-water-influenced stage of the eastern ECS terminated gradually at 10.5-8.5 thousand years B.P. since the warm Kuroshio Current and its branches flowed in the eastern ECS as today. The formation of the postglacial surface-water circulation pattern in the eastern ECS was closely related to the flow patterns of the Kuroshio current. (C) 1999 Elsevier Science B.V. All rights reserved.