The change in redox condition of the Japan Sea since its birth based on trace element geochemistry of sediment cores and sulfur isotope ratio of framboidal pyrite.

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Framboidal pyrite spherules were isolated from high sulfur layrs of a piston core (KH77-3-L4') sample collected from the Japan Basin of the Japan Sea and sulfur isotope ratios of the pyrite-sulfur was measured. The sulfur isotope ratios show as low as-50* indicating the syngenetic formation of framboidal pyrite under euxinic bottom waters and its validity to distinguish the formation of framboidal pyrite under euxinic bottom waters and its validity to distingnish the formation of framboidal pyrite between syngenetic formation under euxinic bottom waters and diagenetic formation through diagenetic sulfate reduction. The C-14 ages of organic carbon were measured at high organic carbon layrs of the core by accelerator mass spectrometry. Twenty seven major and trace element contents were also measured for the core by neutron activation analysis in addition to organic carbon, nitrogen and sulfur. Based on the precise vertical profiles of these chemical parameters, especially of those of redox sensitive elements, the changes of redox conditions of the deep water of the Japan Sea were estimated for the last 35000 years.Organic carbon, nitrogen, total sulfur and 27 major and trace elements were analyzed for 123 samples from and Deep-sea Drilling Core, Leg 127 Site 795 Core, from the Japan Basin of the Japan Sea. Framboidal pyrite spherules were also isolated and the their sulfur isotope ratios were measured. Based on these chemical parameters, the changes in redox conditions of the deep water since the birth of the Japan Sea, ca.15 Ma ago, were estimated. According to these results, the cyclic changes between highly oxic and highly reducing conditions have become significant since 2.4 Ma ago.