Multiproxy reconstruction for Kuroshio responses to northern hemispheric oceanic climate and the Asian Monsoon since Marine Isotope Stage 5.1 (∼88 ka)

Abstract

The Kuroshio, a western boundary current in the northwestern Pacific, plays a key role in regulating ocean and climate in East Asia. The evolution of the Kuroshio and its branches has been the focus of paleoceanographic studies. In this study, we applied a multiproxy (grain size, planktonic foraminiferal species, δ18O, alkenone sea surface temperature (SST) and salinity) reconstruction from sediment core CSH1, which is located at the main axis of the Tsushima Warm Current, a branch of the Kuroshio, in the northern Okinawa Trough (OT). This study, extended the paleoceanographic record of the Kuroshio to Marine Isotope Stage (MIS) 5.1 (∼88 ka) from the far northern site in the OT. Planktonic foraminiferal species identified from this core contain warm-water species related to the Kuroshio and cold-water species related to subarctic water mass. The relative abundances of the warm-water species are high during MIS 1 and MIS 5.1, while cold-water species are high during MIS 2. An organic biomarker proxy, alkenone SST measured from core CSH1 ranges between 21 and 25 °C, with higher values during interglacials (MIS 1, 3.3, 5.1) and interstadials and lower values during glacials and Heinrich (H)/stadial events. Sea surface salinity (SSS) and the depth of the thermocline (DOT), reconstructed based on foraminifera isotopes and faunas, indicate dominant Kuroshio responses to an abrupt climate change event recorded in Greenland ice cores and in stalagmites in East China since ∼88 ka. The CSH1 SSS appears to be mainly controlled by the local river runoff and the Kuroshio, while the DOT change seems to be closely related to the strength of the Kuroshio and the latitudinal shift of the subarctic frontal zone. Our records suggest that, during MIS 1 and MIS 5.1, while global sea level was high, the Kuroshio was dominant; while during MIS 2, MIS 3 and MIS 4, with a low sea level, stronger winter Asian Monsoon (AM) and a more southerly subarctic front played important roles in governing the hydrographic characteristics in the OT. Spectral analysis of our multiproxy hydrographic records shows a dominant precessional period at ∼24 ka. Our hydrographic records, such as SST, SSS and DOT, from a site near the modern Tsushima Warm Current show regional responses corresponding mainly to the global sea level, the Kuroshio, AM and subarctic front, factors which are consistently invoked in the interpretations of other regional records from the OT.