Geophysical and geochemical observations on actively seeping hydrocarbon gases on the south-eastern Yellow Sea continental shelf |
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| Authors: | Email author" target="_blank">K?S?JeongEmail author J?H?Cho S?R?Kim S?Hyun U?Tsunogai |
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| Institution: | (1) Marine Geoenvironment & Resources Research Division, Korea Ocean Research and Development Institute, Ansan P.O. Box 29, 425-600 Seoul, Korea;(2) Environmental Science Laboratory, South Sea Institute, Korea Ocean Research and Development Institute, 391 Jangmok-Ri Jangmok-Myun Koje-Shi, Korea;(3) Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, N10W8 Kita-Ku, 060-0810 Sapporo, Japan |
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| Abstract: | In the southeastern Yellow Sea, active seepage of hydrocarbon gases has been observed by high-resolution (3.5 kHz) seismic profiling both in 1987 and 2001, occurring through a large number of plumes from the topmost pre-Holocene sedimentary layer. It is strong enough to compensate for current speed, extending vertically up to the sea surface. The gas seepage often appears to be explosive to form craters and diapirs, although pockmarks are rare due to the redistribution of mobile palimpsest sands. In core-top seawater and sediments, the gases are characterized by high amounts of C2, homogenous  13C1 values and a large difference (19.7 on average) between 13C1 (–55.2 to –53.6 PDB) and 13C2 (–36.8 to –32.5 PDB) values. The gases are considered to be generated with a smaller amount of C1 at the early thermal cracking stage of labile source materials, after which the C2 gas is enriched in 13C by diffusion or biological alternation at the generation or accumulation site. The homogenous 13C1 values may be one of the geochemical characteristics of gases acquired at depth which are less altered in the case of rapid diffusive gas migration to the seafloor. |
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