Cold-water ostracod fossils from the southern and eastern margins of the Japan Sea

Abstract

The past work regarding the distribution of three representative fossil cold-water ostracod genera in surface sediment of the continental shelf along the southwestern to eastern margin of the Japan Sea is reviewed and summarized. The highest number of cold-water specimens is from the lower continental shelf off Yamaguchi Prefecture, northeast of the Tsushima Strait in the southwestern part of the Japan Sea. These fossils are considered to be the evidence of the southward expansion of their distributional limit during the postmiddle Pleistocene glacial interval, to a latitudinal limit of approximately 10° farther south than the Recent distributional limit of these genera. The presence of these fossil ostracods indicates the prevalence of water similar to the Japan Sea Central Water as far south as the northeast of the Tsushima Strait during the glacial period. This suggests that the summertime water temperature on the upper continental shelf during the glacial period was approximately 10°C lower and salinity 0.5‰ lower than Recent temperatures and salinities. The ostracod data suggest that a cold-water mass different from the Oyashio water was present in the southwestern Japan Sea during the post-middle Pleistocene glacial period.