동해 퇴적물 중 유기화합물 (디플로텐) 검출과 고해양학적 의미

Abstract

Two piston cores (06GHSA P1 and 06GHSA P6) from the Ulleung Basin of the East Sea were examined for the presence of organic compounds (diploptene in particular), and carbon isotopic variations were also analyzed to determine their origins. More than 70 samples from the two cores were analyzed using gas chromatography–mass spectrometry, and 23 samples were selected for carbon isotope analysis based on isotope ratio mass spectrometry. Data from the core records showed that organic compounds occurred in the two cores, showing high vertical fluctuation in the 06GHSA P6 core during the Last Glacial Maximum. The diploptene concentration ranged from 1.7 to 632.1 ng/g (average 87 ng/g) in core 06GHSA P6 and from 1.4 to 42.2 ng/g in core 06GHSA P1 (average 20.1 ng/g). An especially elevated concentration of diploptene was observed in core 06GHSA P6 during glacial periods. Carbon isotope values in the diploptene ranged from –56.33 to –60.23 per mil, suggesting that this diploptene was in part derived from methanotrophic bacteria, which decomposed methane in the water column and sediment. Thus, the occurrence of diploptene derived from bacterial activity and the carbon isotopic values of diploptene may indicate potential methane seepage during the glacial period in core 06GHSA P6. This implies that a potential dissociation of gas hydrate during glacial periods is observed in the foraminiferal isotopic record and methanotrophic processes in the southern part of Ulleung Basin, East Sea.Reasons for the occurrence of diploptene may include paleoceanographic environmental changes such as in sea level during the glacial period. Unlike the Santa Barbara basin in which the episodic light carbon isotopic signals were interpreted as the reason for the warm intermediate water inflow, in the East Sea, the lowered sea level and climatic changes during glacial period may have reduced the stability of the methane hydrate.