Sea-surface temperature and salinity changes in the northwest Pacific since the Last Glacial Maximum

The oxygen isotope records of both benthic and planktonic Foraminifera in five piston cores, collected from the region between the Oyashio and Kuroshio Currents near Japan, clearly show the marked latitudinal shifts of these two currents during the past 25 kyr. Under the present hydrographic condition, a clear relationship between the sea-surface temperature (SST) and oxygen isotope differences from benthic to planktonic Foraminifera is observed in this region. Using this relationship, we find decreased SSTs of 12-13 degreesC (maximum 15 degreesC) in the southernmost core site at the Last Glacial Maximum (LGM), indicating the Oyashio Current shifted southward. The SSTs at the southern two core sites abruptly increased more than 10 degreesC at 10-11 ka, suggesting the Kuroshio Current shifted northward over these sites at 10-11 ka. In contrast, the northern two core sites have remained under the influence of the cold Oyashio Current for the past 25 kyr. With the reasonable estimate of bottom-water temperature decrease of 2.5 degreesC at the LGM, the SSTs estimated by this new method give exactly the same SST values calculated from Mg/Ca ratio of planktonic Foraminifera, allowing palaeosea-surface salinities to be reconstructed. The result suggests that the ice volume effect was 1.0 +/- 0.1parts per thousand at the LGM. Copyright (C) 2004 John Wiley Sons, Ltd.