Abstract
Eight diatom zones are recognized for the uppermost Quaternary piston cores from the Joetsu Basin of the eastern margin of the Japan Sea recovered by a methane hydrate cruise, MD179. They are primarily based on the occurrences of a warm-water marker diatom Fragilariopsis doliolus and a cold-water one Thalassiosira hyperborea and secondarily on that of a new cold-water one Thalassionema umitakae n. sp., and represent major changes of surface water of the Japan Sea. In addition, very fluctuating occurrences of diatom-derived black grains, which might be a proxy of stagnant condition of the sea bottom, first observed in horizons mostly where dark thinly laminated layers are recognized. Because both the diatom zonal subdivision and the occurrence of black grains correlate very well to those of the marine isotope stages, MIS1 through MIS5e recognized by Ishihama et al. (2014) in the same cores examined, it is obvious that they reflect major paleoceanographic changes of the Japan Sea induced by global glacial and interglacial cycles over the last 130 ka. Thalassionema umitakae n. sp. is described in Appendix.
