Sedimentation and environment evolution of the Sea of Japan since the Last Glaciation and its driving forces

Sedimentation processes, environmental variations and driving mechanisms of the Sea of Japan since the Last Glaciation are discussed in this paper on the basis of a comprehensive study of three sediment cores retrieved from the southern, central and western parts of the Sea of Japan. The main findings are as follows. (1) Before 8 ka, terrigenous materials in the southern, central and western parts of the Sea of Japan were mainly coming from rivers, westerly wind and sea ice, respectively. The continuous distribution of volcanic materials in the sediments of the western Sea of Japan since 8 ka is probably related to the formation of the Liman Cold Current, which marks the formation of modern surface circulation pattern of the Sea of Japan. (2) The variations in ventilation characterized by oxygen-depletion in the south and central owe its origin to the strong surface stratification, while well-ventilated condition in the western Sea of Japan related to the active winter sea ice formation. With the eustatic sea level rising after the Last Glacial Maximum, cold and salty waters from the northern East China Sea intruded into the Sea of Japan through the Tsushima Strait during the Heinrich Stadial 1, that facilitate the deep ventilation in the south and central Sea of Japan. However, due to the perennial sea ice cover at the western part of the Sea of Japan, the sedimentary oxygenation declined significantly. During the Late Deglaciation and earlier Holocene, the deep ventilation of the Sea of Japan was dampened in the south but well maintained in the central and west. Generally, the deep ventilation in the entire Sea of Japan has been ameliorated since 8 ka due to the invasion of the high-salinity Tsushima Warm Current. Main driving factors controlling the sedimentary processes and environmental changes in the Sea of Japan are sea level changes, East Asian monsoon (and the westerly wind) and the Tsushima Warm Current, but the responses to the three factors are distinct from place to place. Sea level is the first-order factor that constraints the water exchange between the Sea of Japan and surrounding sea waters. The East Asian summer monsoon brings large amounts of freshwater to the Sea of Japan, while the East Asian winter monsoon controls the sea ice formation and thus the deep water convection. Since 8ka, the Tsushima Warm Current, a more important determinant factor, intruded into the Sea of Japan, which enhanced the exchange between surface and deep waters and thus the renewal rate of oxygen in the deep water and sediments.