Hydrographic changes of the Kuroshio Current in the upper reach area during the past 6000 years

A 6000 year record of planktonic foraminiferal (G. ruber) Mg/Ca ratio and δ18O of Site ORI715-21 (22.7°N, 121.5°E ; 760 m water depth) at centennial resolution off the east coast of Taiwan was obtained. Age model was constructed by NN AMS radiocarbon dating points. The planktonic foraminifera δ18O profile shows a generally depleted trend from -2.4 to -2.8 permil, but Mg/Ca ratio shows a relative stable pattern with an average of ~28 degree C. δ18O values of sea- water were then calculated and show a decreasing trend from ~0.4 to ~0.0 permil during the last 6,000 years. These records indicate a stable sea surface temperature but decreasing salinities in the upper reach area of the Kuroshio current. The results are comparable to that of the Southern Okinawa Trough (MD01-2403) in showing similar pattern. The decreasing trend of SSS appears to be coincident to the tropical and temperate records of the Pacific Ocean but in difference from the East Asian Monsoon (EAM) records indicated by the Chinese speleothem δ18O records, which shows a weakening trend for the last 6,000 years.