The crucial role of deep-sourced methane in maintaining the subseafloor sulfate budget |
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Institution: | 1. Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. Institute for Geology, Center for Earth System Research and Sustainability, Universität Hamburg, Hamburg 20146, Germany;4. Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, Guangzhou 510075, China;5. Key Laboratory of Gas Hydrate, Ministry of Natural Resources, Qingdao Institute of Marine Geology, Qingdao 266071, China |
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Abstract: | Methane (CH4) is a powerful greenhouse gas and its largest reservoir on Earth is held in marine sediments. CH4 in marine sediments is mainly stored in gas-hydrate reservoirs and deep sedimentary strata along continental margins, where large amounts of deep-sourced CH4 ascend to different degrees toward the seafloor. However, the amount of deep-sourced CH4 and its role in subseafloor carbon and sulfur cycling remains poorly constrained. We analyzed sulfate (SO42?) profiles of 157 sites along with previous published 85 sites to determine the regional distribution and amount of SO42? reduction for an area of 1.23 × 105 km2 of the northern South China Sea. Then we compared these obtained results with estimates based on sedimentation rates from the same area. Significantly higher regional SO42? flux estimates based on SO42? profiles (4.26 × 10?3 Tmol a?1), compared to lower estimates based on sedimentation rates (1.23 × 10?3 Tmol a?1), reflect abundant ascending deep-sourced CH4. The difference of the regional SO42? flux estimates (3.03 × 10?3 Tmol a?1) represents the amount of SO42? reduced by CH4 through the anaerobic oxidation of CH4 (AOM). Deep-sourced CH4 contributes 71% to total SO42? consumption in the study area, largely exceeding SO42? consumption by organoclastic sulfate reduction. Our findings substantiate that deep-sourced CH4 governs subseafloor carbon and sulfur cycling to a previously underrated extent, fueling extensive chemosynthesis-based ecosystems along continental slope and rise. |
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Keywords: | Deep-sourced methane Sulfate reduction Anaerobic oxidation of methane Sulfate profiles South China Sea |
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