Terrestrial biomarkers in the sediment of the East Sea (Japan Sea) since the MIS 11: implications for paleoproductivity and paleoclimatic changes

Abstract:

Terrestrial biomarkers such as n-alkanes and cholesterol were analyzed to infer the variations of paleoproductivity and the corresponding paleoclimatologic information from the sediment of the Korean Plateau, East Sea (Japan Sea) since the Marine Isotope Stage (MIS) 11 (ca. 400 ka). Previous studies of SST variation have shown that glacial-interglacial scale changes were quite variable with the maximum range of 26^oC in MIS 7, and the minimum range of 12^oC during MIS 2 and 6. The distribution of terrestrial n-alkanes signatures is characterized by the occurrence of high odd number frequency with a minor contribution of specific compound (nC₂₇ only). Average Chain Length (ACL) and Carbon Preferences Index (CPI), both of which are derived from n-alkane combination, show similar shifting between glacial and interglacial periods. This suggests that paleovegetation communities had been changed in responding to paleoclimatological variations, and the input amount of terrestrial compound was strongly linked with paleoclimatologic changes. In particular, depleted values of δ¹³C_org during MIS 2, 8 and 10 were coincident with lower nitrogen isotope values indicating local paleoceanographic effects such as paleoproductivity changes. Decoupling between δ¹³C_org and δ¹⁵N_org during MIS 1, 3, 5, 7 and coupling of the two during MIS 8 and 11 can be observed, which appear to be interpreted as local productivity changes. In particular, high abundance of cholesterol and C₂₁ n-alkanes, which were derived from diatom, increased during interglacial periods. Therefore, alkenones, SST and n-alkanes signatures coincide with δ¹³C_org and δ¹⁵N_org variations during glacial-interglacial cycles and further strongly associated with cholesterol abundance suggesting that the paleoenvironmental conditions in East Sea during glacial-interglacial periods were sensitive not only to global climate changes but also to local paleceanographic variations. Surface water circulation around the Korea Plateau associated with eustatic sea-level changes may have been linked with paleoproductivity changes, at least on the Korea Plateau of the East Sea (Japan Sea) since the last MIS 11.