Carbon cycling within the sulfate-methane-transition-zone in marine sediments from the Ulleung Basin Public Deposited

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  • The significance of the various carbon cycling pathways in driving the sharp sulfate methane transition (SMTZ) observed at many locations on continental margins is still a topic of debate. Unraveling these processes is important to our understanding of the carbon cycle in general and to evaluate whether the location of this front can be used to infer present and past methane fluxes from deep reservoirs (e.g., gas hydrate). Here we report the pore water data from the second Ulleung Basin Gas Hydrate Expedition (UBGH2) and on the results of a box model that balances solute fluxes among different carbon pools and satisfies the observed isotopic signatures. Our analysis identifies a secondary methanogenesis pathway within the SMTZ, whereby 25 to 35% of the dissolved inorganic carbon (DIC) produced by the anaerobic oxidation of methane (AOM) is consumed by CO₂ reduction (CR). To balance this DIC consumption, a comparable rate of organic matter degradation becomes necessary, which in turn consumes a significant amount of sulfate. The fraction of sulfate consumed by AOM ranges from 70 to 90%. Whereas a simple mass balance would suggest a one to one relationship between sulfate and methane fluxes; our isotopic considerations show that methane flux estimates based solely on sulfate data may be in error by as much as 30%. Furthermore, the carbon cycling within the SMTZ is fueled by a significant contribution (10-40%) of methane produced by organic matter degradation just below the SMTZ. Therefore AOM rates cannot necessarily be used to infer methane contributions from gas hydrate reservoirs that may lay tens to hundreds of meters below the SMTZ.
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  • Hong, W. L., Torres, M. E., Kim, J. H., Choi, J., & Bahk, J. J. (2013). Carbon cycling within the sulfate-methane-transition-zone in marine sediments from the Ulleung Basin. Biogeochemistry, 115(1-3), 129-148. doi:10.1007/s10533-012-9824-y
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  • 115
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  • 43468
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  • This project was made possible with the funding support from Korea Institute of Geosciences and Mineral Resources (KIGAM) (GP2012-026) and US Department of Energy, National Energy Technology Lab under RES contract (DE-FE0004000).
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