가스하이드레이트가 부존하는 퇴적층에서 황산염환원-메탄산화 경계면의 특성

Abstract

Sulfate reduction-methane oxidation interface (SMI) due to anaerobic methane oxidation is an important factor controlling sulfate depletion in the methane hydrate bearing or methane rich sediments. Porewater samples obtained from the two types of sediments (methane hydrate-bearing and free-gas saturated sediments) in the NE Sakhalin slope and Derugin Basin during the 2003 CHAOS expeditions (a joint effort among Japan, Russia, Germany, Belgium and Korea). We measured sulfate and methane concentration and organic matters.Low concentrations of methane (0.001-0.01 ml/l wet sediment) show above subbottom depth of about 2 m. Methane concentrations sharply increase up to 650 ml/l at the deeper depth of 4-6 m, whereas sulfate concentrations in pore waters decrease generally downward from 28.9 mM (near surface) to 0.5 mM (deeper layer). It appears that SMI migrates to upward inside the major gas flare sites, e.g CHAOS Structure (ca. 60 cm below the seafloor), Hieroglyph Structure (200-300 cm below the seafloor) and Kitami Structure (60-170 cm below the seafloor). In the Derugin Basin, where methane concentration is low, the SMI (ca. 300 cm below the seafloor) is deeper than gas seeping area. Consequently, as methane increases explosively, sulfate concentrations decrease sharply, and the depth of the SMI would be affected by both methane supply from the deeper area in the NE Sakhalin slope.