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Flux and distribution of methane (CH4) in the Gunsan Basin of the southeastern Yellow Sea, off the Western Korea Part A Toxic/hazardous substances & environmental engineering

Lee, Jun-Ho, Woo, Han Jun, Son, Seung-Kyu, Kim, Moonkoo, Lee, Dong-Hun, Tsunogai, Urumu, Jeong, Kap-Sik
Journal of environmental science and health 2018 v.53 no.5 pp. 457-466
basins, coasts, methane, seawater, sediments, Korean Peninsula, Yellow Sea
The flux and distribution of methane (CH₄) was investigated in the seawater column at 14 stations in the Gunsan Basin, the southeastern part of Yellow Sea from 2013 to 2015. Here CH₄ is concentrated 2.4–4.7 (3.4 ± 0.7) nM in the surface and 2.5–7.4 (5.2 ± 1.7) nM in the bottom layer. The CH₄ saturation ratios ranged from 65.5% to 295.5% (162.6 ± 68.7), comprising the mean sea-to-air CH₄ flux of 3.8 to 25.3 (15.6 ± 5.5) µM m⁻²d⁻¹. Methane concentration was largely different in the upper and the lower seawater layers that is separated by the thermocline of which depth is variable (20–60 m) depending on the time of sampling. The concentration of seawater dissolved CH₄ is high between the bottom surface of the thermocline layer and the sea floor. Generally it tends to decrease from the south-westernmost part of the basin toward the west coast of Korea. This distribution pattern of CH₄ seems to result from the CH₄ supply by decomposition of organic matters produced in the upper seawater layer that is superimposed by the larger supply from the underlying sediment layer especially beneath the thermocline. The latter is manifested by ubiquitous CH₄ seeps from the seafloor sediments.