PALEOCEANOGRAPHIC EVOLUTION OF THE JAPAN SEA

Multidisciplinary studies on nearly continuous hemipelagic sequences r ecovered from the deeper parts of the Japan Sea during ODP Leg 127/128 in 1989 yielded new information on the paleoceanographic conditions o f the sea since its establishment as a deep marginal basin of signific ant size approximately at 20 Ma. By synthesizing these new information on surface and bottom water conditions, CCD, biogenic silica accumula tion, and paleogeography, it is possible to reconstruct changes in pal eo-ocean circulation within the sea. It is also possible to specify th e ultimate cause of such changes by comparing their timing and nature with those of global paleoceanographic as well as local tectonic event s.The result of our synthesis suggests that the Japan Sea has been res ponding to the high frequency changes of global surface conditions in very sensitive manner throughout its history. However, the mode of its response changed from time to time. The changes in response mode have been strongly influenced by such factors as sill depth, position of c hannels, and the degree of closure of the sea, which were controlled e ither by local tectonism or global eustatic sea level changes.