Palynological study of paleoclimate and paleoceanographic changes in the Eastern South Korea Plateau, East Sea, during the Plio-Pleistocene climate transition

Abstract

A palynological study was performed using the core obtained from the Integrated Ocean Drilling Program (IODP) Expedition 346 Site U1430 in the Eastern South Korea Plateau in the East Sea, to reveal variability of paleoclimate and paleoceanography during the late Pliocene to early Pleistocene climate transition period (56.0–68.0 meters below sea floor [mbsf]). Two pollen and dinocyst zones are established with a boundary at ca. 3.0 Ma. Prior to ca. 3.0 Ma (first pollen and dinocyst zone), long-term oscillation of the East-Asian winter monsoon (EAWM) is indicated by fluctuations in the abundance of pollen taxa, representing cold–dry and cool–wet climates. After ca. 3.0 Ma (second pollen and dinocyst zone), an increase in cold–dry conifer pollen indicates an enhanced and stable EAWM. In addition, the prevalence of the xerophytic herb, Artemisia, increases markedly after 3.0 Ma, suggesting open grassland on the exposed South Yellow Sea shelf during the sea level lowstand under cold–dry climate conditions. Artemisia pollen are interpreted as having been delivered to the coast through fluvial channels in this grassland environment, and subsequently transported to the East Sea by inflow of a weak Tsushima Warm Current (TWC) through the narrow Korea Strait. The TWC intrusion signal is represented by an influx of Tuberculodinium vancampoae, a warm water dinoflagellate species, in the western Pacific region. The high abundances of cold–dry conifer pollen and cold water dinocyst elements after ca. 2.8 Ma suggest an intensified EAWM. Meanwhile, a short-term increase in moisture-loving Tsuga pollen after ca. 2.5 Ma was likely due to soil moisture derived from snowfall caused by evaporation of heated seawater from the weak TWC in the East Sea under cold climate conditions. The palynological studies reported here help verify the linkages between the EAWM, TWC, precipitation and vegetation responses in/around the East Sea region.