Radiolarians of the Japan Sea

Japan Sea ODP Leg 127 shipboard radiolarian biostratigraphic data are compiled and improved. The sequence of biostratigraphic events determined in sediments above the opal-A/opal-CT transition is illustrated graphically with depth-depth plots. The absence of biostratigraphic indicators from the North and subtropical Pacific and differences between the compositions of the Japan Sea and Pacific radiolarian assemblages suggest that the planktonic populations of the Japan Sea have been partially isolated from the Pacific since the late Miocene. Subtropical fauna in sediments younger than ~1.8 Ma at Site 797 record the occurrence of a paleo-Tsushima current. These same fauna record larger volumes of the paleo-Tsushima current, or warmer intervals during the colder glacial climate regime at Site 794. The variability of Pleistocene assemblage composition and preservation shows that radiolarian dissolution has played a large part in determining what is preserved. Preliminary taxonomic evaluations are made, and the stratigraphic and paleoceanographic implications of radiolarian species are discussed.