Using sediment geochemistry to infer temporal variation of methane flux at a cold seep in the South China Sea |
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| Institution: | 1. CAS Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;2. Department of Earth Sciences and Geological Engineering, Sun Yat-Sen University, Guangzhou 510275, China;3. Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China;4. Guangzhou Marine Geological Survey, Guangzhou 510740, China;1. CAS Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;2. CAS Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. State Key Laboratory of Biogeology and Environmental Geology, Wuhan, Hubei 430074, PR China;2. School of Earth Science, China University of Geosciences, Wuhan, Hubei 430074, PR China;3. University of Texas at Austin, Austin, TX 78712, USA;4. Guangzhou Marine Geological Survey, Guangzhou, Guangdong 510769, PR China;5. Qingdao Institute of Marine Geology, Qingdao, Shandong 266071, PR China;1. State Key Laboratory of Biogeology and Environmental Geology, Wuhan, Hubei 430074, PR China;2. School of Earth Science, China University of Geosciences, Wuhan, Hubei 430074, PR China;3. National Institute for South China Sea Studies, Haikou, Hainan 571100, PR China;4. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, Hubei 430074, PR China;5. Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA;6. Guangzhou Marine Geological Survey, Guangzhou, Guangdong 510769, PR China;7. Qingdao Institute of Marine Geology, Qingdao, Shandong 266071, PR China;1. CAS Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;2. Universität Wien, Department für Geodynamik und Sedimentologie, Althanstrasse 14, 1090 Wien, Austria;3. Department of Biology, Hong Kong Baptist University, Hong Kong, China;4. School of Ocean and Earth Sciences, Tongji University, Shanghai, China;5. Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA;6. CAS Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;7. University of Chinese Academy of Sciences, Beijing 100049, China;1. MLR Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, China Geological Survey, Guangzhou 510070, China;2. Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China;3. CAS Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;4. Institute of Geology, University of Hamburg, 20146 Hamburg, Germany;5. Department of Geodynamics and Sedimentology, University of Vienna, 1090 Vienna, Austria;1. Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai, 201306, China;2. CAS Key Laboratory of Ocean and Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China;3. Institute for Geology, Center for Earth System Research and Sustainability, Universität Hamburg, 20146, Hamburg, Germany |
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| Abstract: | Release of methane from the seafloor throughout the world's oceans and the biogeochemical processes involved may have significant effects on the marine sedimentary environment. Identification of such methane release events in marine sediment records can hence provide a window into the magnitude of ancient seeps. Here, we report on analysis of the geochemical composition of samples in a 12.3 m long sediment core (DH-5) collected from a seep site in the South China Sea (SCS). Our aim has been to investigate whether the evidence for the presence of methane release event within sediments is discernible from solid-phase sediment geochemistry. We show that sedimentary total sulfur (TS), δ34S values of chromium reducible sulfur (δ34SCRS) along with total organic carbon (TOC) and total inorganic carbon (TIC) content can be used to infer the presence of methane release events in cold seep settings. At least three methane release events were identified in the studied core (Unit I at 400–550 cm, Unit II at 740–820 cm, and Unit III at 1000–1150 cm). According to the characteristic of redox-sensitive elements (eg., Mo, U and Mn), we suggest that methane flux has been changed from relatively high (Unit I) to low (Unit II and III) rates. This inference is supported by the coupled occurrence of 34S-enriched sulfides in Unit II and III. AMS 14C dates from planktonic foraminifera in Unit I suggest that high methane flux event occurred at ∼15.4–24.8 kyr BP, which probably resulted in locally-focused aerobic methane oxidation. Overall, our results suggest that TS, TOC, TIC and δ34SCRS have potential for identifying present and fossil methane release events in marine sediments. |
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| Keywords: | Cold seep Anaerobic oxidation of methane Sulfur isotope South China Sea |
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