Paleoceanographic Variation inferred from the carbon and nitrogen isotope of organic matters in the East Sea since the last 400 kyr

Abstract

Carbon and nitrogen isotope of organic matter, and total organic carbon (TOC) and inorganic carbonate content of a piston core taken from the East Sea (Japan Sea) were investigated to understand the paleoceanographic variations since the last 400 kyr. Oxygen isotope signals of foraminifera shows large fluctuation, ranging from MIS (Marine Isotope Stage) 1 to MIS 11 with a distinctive glacial-interglacial variation. Comparison of oxygen isotopic records during the 400 kyr reveals that paleoceanographic changes in the East Sea were quite different from those of open oceans. The oxygen isotope data during the MIS 2, 6, and 8 consistently show depleted signatures, indicative of surface-water freshening. The content of biogenic carbonate, TOC and carbon and nitrogen isotope of organic matter (δ13C and δ15N) were determined and used to interpret paleoenvironmental changes. Based on the isotopic composition of δ13C and δ15N, which showed extreme temporal variation since MIS 11 influx of large amount of terrestrial organic matters from the neighboring continent during MIS 2, 8 and 10 can be implied. However, during MIS 6, it did not show any significant terrestrial input suggesting that the paleoceanographic condition during MIS 2, 8, 10 and 6 is different in terms of carbon isotope source. In particular, depleted values of δ13C during MIS 2, 8 and 10 were coincident with lower nitrogen isotoe last 400 kyr. Oxygen isotope signals of foraminifera shows large fluctuation, ranging from MIS (Marine Isotope Stage) 1 to MIS 11 with a distinctive glacial-interglacial variation. Comparison of oxygen isotopic records during the 400 kyr reveals that paleoceanographic changes in the East Sea were quite different from those of open oceans. The oxygen isotope data during the MIS 2, 6, and 8 consistently show depleted signatures, indicative of surface-water freshening. The content of biogenic carbonate, TOC and carbon and nitrogen isotope of o