Palynological implications for the paleoclimate and paleoceanographic reconstruction of the East Sea since the early Pleistocene at IODP site U1430

Abstract

Palynomorphs, including pollen and dinoflagellate cysts from marine sediments, can provide a history of paleoclimate and paleoceanography. We present new palynological profiles based on a core from the Integrated Ocean Drilling Program Site U1430, which was drilled in the Ulleung Plateau East Sea. This core covers the past 2 Ma and spans the Mid-Pleistocene Transition (MPT, 1.2–0.8 Ma) and Mid-Brunhes Event (MBE, ∼0.43 Ma). Terrestrial and marine palynomorph records indicate orbital-scale variations in paleoclimate and paleoceanography, reflecting changes in the interconnections between vegetation, climate, and the ocean. Before the MPT, the high pollen taxa ratio and abundant temperate pollen suggest a relatively warm temperature associated with astronomical forcing-induced insolation changes. At ca. 1.3 Ma, boreal coniferous pollen increased, suggesting intensification of the East Asian winter monsoon (EAWM). The long-term trend of boreal coniferous pollen concentration was similar to that of benthic δ18O. This orbital scale boreal conifer pollen assemblage variation indicates Quaternary EAWM evolution controlled by changes in global ice volume and climatic cooling. The marine palynological data reflect the ocean circulation history of the study area, where sea level fluctuations and tectonic activity played important roles around the marginal sea. The abundance of warm-water dinoflagellate species after ca. 1.9 Ma, including Tuberculodinium vancampoae, indicates Tsushima Warm Current intrusion related to the expansion of the Korea (Tsushima) Strait. Nematosphaeropsis labyrinthus and other cold-water species increased markedly during the MPT, suggesting a low sea surface temperature and weakened vertical mixing of the East Sea due to the cooled climate and sea ice during the MPT. The marked sea level fluctuation associated with the glacial–interglacial cycling after the MBE resulted in an assemblage composition shift from cold to warm water species. Tsuga and Betula thrived during mild winters, primarily influenced by winter insolation. These genera were particularly prosperous in the early Pleistocene, coinciding with a strong intrusion of the Tsushima Warm Current (TWC). Our findings should be considered in developing a comprehensive understanding of the paleoclimate and paleoceanographic history of northern East Asia across the major climate transitions of the Pleistocene.