Pore-water geochemistry in methane-seep sediments of the Makran accretionary wedge off Pakistan: Possible link to subsurface methane hydrate |
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| Authors: | Xianrong Zhang Jianming Gong Zhilei Sun Jing Liao Bin Zhai Libo Wang Xilin Zhang Cuiling Xu Wei Geng |
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| Institution: | 1.Key Laboratory of Gas Hydrate of Ministry of Natural Resources, Qingdao Institute of Marine Geology, Qingdao 266071, China2.Evaluation and Detection Technology Laboratory for Marine Mineral Resources, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China |
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| Abstract: | Cold seeps are pervasive along the continental margin worldwide, and are recognized as hotspots for elemental cycling pathway on Earth. In this study, analyses of pore water geochemical compositions of one ~400 cm piston core (S3) and the application of a mass balance model are conducted to assess methane-associated biogeochemical reactions and uncover the relationship of methane in shallow sediment with gas hydrate reservoir at the Makran accretionary wedge off Pakistan. The results revealed that approximately 77% of sulfate is consumed by the predominant biogeochemical process of anaerobic oxidation of methane. However, the estimated sulfate-methane interface depth is ~400 cm below sea floor with the methane diffusive flux of 0.039 mol/(m2·a), suggesting the activity of methane seepage. Based on the δ13CDIC mass balance model combined with the contribution proportion of different dissolved inorganic carbon sources, this study calculated the δ13C of the exogenous methane to be ?57.9‰, indicating that the exogenous methane may be a mixture source, including thermogenic and biogenic methane. The study of pore water geochemistry at Makran accretionary wedge off Pakistan may have considerable implications for understanding the specific details on the dynamics of methane in cold seeps and provide important evidence for the potential occurrence of subsurface gas hydrate in this area. |
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| Keywords: | Makran accretionary wedge methane-seep pore water geochemistry anaerobic oxidation of methane |
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