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Wang M.,CAS Qingdao Institute of Oceanology | Wang M.,State Key Laboratory of Gas Hydrates | Wang M.,Yangtze University | Cai F.,CAS Qingdao Institute of Oceanology | And 14 more authors.
Science China Earth Sciences | Year: 2015

The anaerobic oxidation of methane (AOM) has strongly developed at Core A, Site 79 of the middle Okinawa Trough, East China Sea, and a large amount of authigenic pyrite is preserved in the surface sediment. In this study, we analyze the characteristics of the authigenic pyrite and its sulfur isotopic values. The authigenic pyrite is stripy and tubular, and there were foraminifera compartments filled with pyrite. The pyrite is extracted using chromium reduction, and the values of δ34S are found to lie between -41.20‰ and 8.92‰ V-CDT. The bulk pyrite tends to be more enriched in 34S with increasing depth. Particularly, the δ34S value of the pyrite lies between -32.73‰ and -41.20‰ V-CDT above 278 cmbsf, but it quickly increases below this depth (-21.49‰–8.92‰ V-CDT). At the same time, the total sulfur content of the pyrite shows an abrupt increase above 100 cmbsf but is otherwise stable between 1.04% and 0.55% below 100 cmbsf. The stable and negative values of δ34S and the decreasing values of total sulfur above 278 cmbsf indicate reduced AOM activities in 17.18–5.3 ka. In addition, the increasing δ34S and pyrite content indicate strong AOM development and methane seep below 278 cmbsf in 18.8–17.18 ka. In particular, the highest positive value of δ34S occurring in 18.78 ka indicates the most intense AOM activity. The shallow sulfate-methane interface (SMI) and high methane flux below marine sediments also strongly support this activity. © 2015, Science China Press and Springer-Verlag Berlin Heidelberg. Source

Li Q.,State Key Laboratory of Gas Hydrates | Li Q.,CAS Qingdao Institute of Oceanology | Cai F.,State Key Laboratory of Gas Hydrates | Cai F.,CAS Qingdao Institute of Oceanology | And 13 more authors.
Science China Earth Sciences | Year: 2015

Anaerobic oxidation of methane and sulfate reduction was studied in the pore waters of four cores at two stations of the middle Okinawa Trough. Pore water vertical distributions of sulfate, methane, sulfide, total alkalinity, ammonium, and phosphate were determined in this study. Our results show strong linear sulfate concentration gradients of 6.83 mmol m−1 in Core A and 5.96 mmol m−1 in Core C, which were collected from two stations. Concurrent variations of methane, total alkalinity and hydrogen sulfide all exhibit steep increases with depth at both cores, which indicate active methane seep activities around two stations. Pore water ammonium and phosphate concentrations reveal minor influences of organic matter degradation on sulfate reduction at two stations. Sulfate methane interface (SMI) was extrapolated from linear sulfate profiles in methane seep cores. Shallower SMI depths (A: 4.9 mbsf; C: 5.4 mbsf) indicate strong methane fluxes and active anaerobic oxidation of methane in the underlying sediments. © 2015, Science China Press and Springer-Verlag Berlin Heidelberg. Source

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