Early Pleistocene evolution of the Japan Sea Intermediate Water

Abstract

AbstractThe Early Pleistocene fossil record of the Japan Sea reveals that the planktonic foraminifer Globorotalia inflata succeeded in expanding its range from the East China Sea to the Japan Sea during interglacial stages of the Early Pleistocene; however, the species is only found in surface sediment samples from the southwestern‐most part of the sea. Based on the ecology of G. inflata and the water mass structure of the Japan Sea, it appears that its geographical distribution is mainly controlled by the low temperature of the intermediate water, which is caused by the cool‐water mass of Japan Sea Proper Water. The temporal and spatial patterns of G. inflata occurrence indicate that the intermediate water at 200 m depth during interglacial stages between 1.46 and 1.3 Ma was warmest during the Quaternary. This warm intermediate water probably resulted from the influence of the low‐salinity nature of the Tsushima Current due to the large inflow of East China Sea Coastal Water. After 1.3 Ma, the intermediate water at 200 m depth became cooler in a step‐wise manner. This cooling can be explained by an intensification of thermohaline circulation in the Japan Sea associated with strengthening of the East Asian winter monsoon and an increase in salinity due to enlargement of the southern strait. Copyright © 2009 John Wiley & Sons, Ltd.