Late Quaternary course changes of the Kuroshio Current in the Ryukyu Arc region, northwestern Pacific Ocean

Abstract

The existence of a land bridge connecting the central-southern Ryukyu Arc to Taiwan during the last glacial stage (oxygen isotope stages 2 to 4) and its postglacial disappearance are demonstrated by variations in the planktic δ18O values and the frequency of Pulleniatina in 11 piston cores from the Okinawa Trough region. The upward increase in the Pulleniatina group in the cores signals the progressive inflow of the Kuroshio Current into the Okinawa Trough area, because this group is characteristic of the Kuroshio Current, as revealed here by planktic foraminiferal distribution using 56 surface sediment samples collected from the whole area of this region. The Ryukyu-Taiwan land bridge caused eastward deflection of the Kuroshio Current at the southern end of the Ryukyu Arc. A Pulleniatina minimum event in the period from ~4500 to 3000 yr B.P. is recognized in 10 cores from the Okinawa Trough and one from the northern Ryukyu Trench slope. In contrast to the LGM, the decline of Pulleniatina in this event was not ascribed to cyclic climate changes such as worldwide cooling but to the formation of a barrier between Taiwan and the southern Okinawa Arc. However, this regional event influences largely on the Holocene climate of Japan and its adjacent seas.