Late Pleistocene Geochemical Stable Isotope Records from IODP Expedition 346 in the Japan Sea/East Sea and East China Sea

Numerous studies have shown that geochemical analyses of sedimentary organic matter (OM) can be used as a geological tool for paleoceanographic and paleoproductivity reconstructions. Expedition 346 of the Integrated Ocean Drilling Program (IODP) was conducted in the Japan Sea/East Sea and East China Sea in 2013 and obtained continuous sedimentary sequences with the overall objective of reconstructing the onset and nature of the East Asian Monsoon (EAM) on orbital and millennial timescales within the last 5 Myr. These sedimentary sequences show distinctive alternations of light and dark colored layers, especially within the last 2.5 Myr, that will enable investigation into the correlation between the EAM and climate dynamics in the Japan, Yamato, and Ulleung basins. In this study, we analyzed 1,750 geochemical samples for %CaCO3, %C, δ13C, %N, and δ15N from three Expedition 346 sampling sites (U1426 and U1427 in the Japan Sea/East Sea, and U1429 in the East China Sea) in order to reconstruct changes in the organic matter sources with the goal of determining the nature of nutrient cycling and deep oceanic circulation during the Late Pleistocene. Carbonate concentration ranges from 0-45%, organic carbon 0.5-6.4%, δ13C -25.8-20‰, %N 0.05-0.4%, and δ15N 3.3-10.5‰. Site U1426 shows the greatest variation in all five geochemical analyses, likely due to its location above the CCD and near complete isolation from the Pacific Ocean and other marginal seas during glacial periods. Site U1429 does not share similar geochemical trends as the other two sites since it is located outside of the Japan Sea/East Sea and does not become isolated during glacial-eustatic sea level changes. Additionally, U1429 is affected by changes in the Kuroshio current and terrigenous inputs from Yangtze River. In all three study sites, interglacial/interstadial periods show increased paleo-productivity than during glacial low stands.