Spatial and temporal variation of geochemical properties and paleoceanographic implications in the South Korea Plateau (East Sea) during the late Quaternary

Abstract

Geochemical (opal, total organic carbon (TOC), and CaCO 3) analyses of three sediment cores from the South Korea Plateau in the East Sea (Japan Sea) revealed that the late Quaternary (<190 kyr BP to the present) paleoceanographic conditions are characterized by the orbital variations of geochemical properties that have recorded the changes of surface- and bottom-water conditions. Chronostratigraphy of the sediment cores was accomplished by the direct correlation of L * values to the well-dated core MD01-2407 in Oki Ridge, supplement to the AMS 14C dates, well-known lithostratigraphic and tephrostratigraphic markers. Biogenic opal concentrations are high during Marine Isotope Stage (MIS) 1 and MIS 5.5, and low during the glacial period, suggesting that diatom production was enhanced during the warm period when the surface-water exchange between the East Sea and adjacent marginal seas was active. In contrast, glacial opal paleoproductivity appears to have been depressed, probably because of insufficient nutrient availability, resulting from limited vertical ventilation. Overall TOC contents follow the orbital variations; high during the interglacial and relatively low during the glacial time. However, high-resolution TOC fluctuations are independent of opal concentration, which may be attributed more to the preservation of organic matter rather than to the surface-water production. The high TOC contents in the thin dark mud (i.e., TL) layers may be due to the enhanced surface-water production as well as the intensified bottom-water anoxia. On the other hand, high CaCO 3 contents associated with the TL layers during the glacial and stadial period may be attributed to the reduced dissolution. The temporal variations of these geochemical properties are likely to follow the global orbital cycles, indicating the significant changes of surface- and bottom-water properties due to the eustatic sea-level fluctuations between the interglacial and glacial period. The comparable values of these geochemical properties among the sediment cores suggest that the spatial paleoceanographic conditions in the South Korea Plateau were consistent and uniform during the late Quaternary, in spite of a little local discrepancy in amounts of properties and timing of events.