Paleoceanographic history around the Tsugaru Strait between the Japan Sea and the Northwest Pacific Ocean since 30 cal kyr BP

The paleoceanographic history around the Tsugaru Strait since 30.0 cal kyr BP was reconstructed using ecological and biogeographical habitats of diatom species and Q-mode factor analysis of diatom flora in six piston cores. At 30.0–17.5 cal kyr BP, a fall in sea level and the intensification of the Oyashio Current caused erosion of submarine sediments near the shore in the eastern area of the Strait and led to deposition of the third and second sequences of thinly laminated layers (TL3 and TL2) in the Japan Sea. At 17.5–11.5 cal kyr BP, cooling intensified around the Strait, producing an inflow of Oyashio water into the Japan Sea through the Strait. At 15.5–14.5 cal kyr BP, a cold-water mass around the Strait developed from subarctic sea-ice to arctic waters. At 13.0–11.2 cal kyr BP, the Younger Dryas cooling was clearly recorded by the increasing of oceanic cold-water diatom species in the eastern area of the Tsugaru Strait but not in the Japan Sea. At 15.5–13.0 cal kyr BP and 11.25–10.25 cal kyr BP, the warming around the Younger Dryas resulted in the deposition of thinly laminated layers off Shimokita in the eastern area of the Strait. At 9.5 cal kyr BP, the Oyashio Current water intruded into deep depths in the mixed water region off Sanriku. At 9.5–7.0 cal kyr BP, the fluctuation of 1.5-kyr intervals in the strength of the Tsushima Warm Current system in the Japan Sea was initiated.