Assessment of shallow methane (CH4) gas using stable carbon and hydrogen isotopes in the sediments of the Gunsan Basin, eastern-central Yellow Sea, off the southwest of Korea

Abstract

In the Gunsan Basin, eastern-central Yellow Sea (YS), gas seepages were observed from the uppermost sedimentary layer charged locally with gases that are important indicators of marine resources, environmental changes, and geo-hazards. Methane (CH4) among the gases is the most abundant organic compound in the Earth’s atmosphere, where it acts as a greenhouse gas and thus has implications for global climate change. Headspace CH4 was determined in surface and core sediments in order to understand the C- and H- isotopes signatures in the Gunsan Basin that were collected onboard R/V Onnuri and Eardo in 2013 to 2015. The surface sediments contain 0.2 to 16.9 &micro M CH4 that are mostly produced by microbial fermentation of organic materials in shallow depth, as indicated by the light values of δ13CCH4 (&#8211 70.2~-50.7‰ VPDB). CH4 is actively seeping mainly in the western central part of the Gunsan Basin where the underlying sedimentary layers are thick and heavily faulted. In the cores, CH4 is concentrated 1 to 20 μM through the core depths without any relationships to grain size, organic matter contents. Largely different from those, δ13CCH4 ranges in &#8211 62.0~-18.0‰ VPDB (δ2DCH4 range in &#8211 296.0~-144.0‰ VSMOW), that is, strongly mixed CH4 of thermogenic and biogenic origins in the core sediments. The CH4 flux at the sediment-water interface (SWI) using Fick’s first law of diffusion was calculated 2~2ane (CH4) among the gases is the most abundant organic compound in the Earth’s atmosphere, where it acts as a greenhouse gas and thus has implications for global climate change. Headspace CH4 was determined in surface and core sediments in order to understand the C- and H- isotopes signatures in the Gunsan Basin that were collected onboard R/V Onnuri and Eardo in 2013 to 2015. The surface sediments contain 0.2 to 16.9 &micro M CH4 that are mostly produced by microbial fermentation of organic materials in shallow depth, as indicated by the light values of δ13CCH4 (&#8211 70.2~-50.7‰ VPDB). CH4 is actively seeping mainly in the western central part of the Gunsan Basin where the underlying sedimentary layers are thick and heavily faulted. In the cores, CH4 is concentrated 1 to 20 μM through the core depths without any relationships to grain size, organic matter contents. Largely different from those, δ13CCH4 ranges in &#8211 62.0~-18.0‰ VPDB (δ2DCH4 range in &#8211 296.0~-144.0‰ VSMOW), that is, strongly mixed CH4 of (중략)