Orbital- and millennial-scale paleoceanographic changes in the north-eastern Japan Basin, East Sea/Japan Sea during the late Quaternary

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Two gravity sediment cores (GH99-1239 and GH99-1246) obtained from the north-eastern Japan Basin in the East Sea/Japan Sea were analyzed for the orbital- and millennial-scale paleoceanographic changes. Chronostrati- graphically, core GH99-1239 represents a continuous sedimentary record since 32 ka, based on correlation of distinct lithological markers (i.e. dark layer or TL layer) with those in core GH98-1232 collected nearby. For core GH99-1246, the age model is constructed through correlation of lightness (L � ) values and tephra (Aso-4 and Toya) layers with those in the well-dated Oki Ridge core (MD01-2407), indicating about 134 ka of sedimentation since the latest Marine Isotope Stage (MIS) 6. New geochemical data from both cores corroborate orbital-scale paleoceanographic variation, such that surface-water productivity, represented by biogenic opal and total organic carbon (TOC) contents, increased during MIS 1 and MIS 5; CaCO3 contents do not show such distinct glacial-interglacial cycles, but were influenced by dissolution and preservation rather than foraminiferal production. During the glacial periods when sea ice was prevalent, surface- water productivity was low, and bottom-water conditions became anoxic, as indicated by high total sulfur (TS) contents and high Mo concentrations. The geochemical data further document millennial-scale paleoceanographic variability, corresponding to a series of thin TL layers in response to Dansgaard-Oeschger cycles but irrespective of the glacial or interglacial periods. In particular, thin TL layers formed during MIS 3 are characterized by less TOC (about 1%) and TS (about 0.4%) contents and lower Mo (about 5 p.p.m.) concentration, whereas those during MIS 4 and MIS 5 exhibit more TOC (up to 4%) and TS (up to 5%) contents and higher Mo (up to 120 p.p.m.) concentration. Such a discrepancy is attributed to different degree of surface-water productivity and of bottom-water oxygenation, which is closely related to the sea level position and extent of ventilation. Flux of the East China Sea Coastal Water controlled by millennial-scale paleoclimatic events is the most critical factor in deciding the properties of TL layers in the north-eastern Japan Basin. Our results strongly confirm that TL layers in the Japan Basin also validate the unique feature of basin-wide paleoceano- graphic signals in the East Sea/Japan Sea. Copyright # 2011 John Wiley & Sons, Ltd.