Carbon cycling within the upper methanogenic zone of continental rise sediments; An example from the methane-rich sediments overlying the Blake Ridge gas hydrate deposits

摘要: Data from piston cores collected Carolina Rise and Blake Ridge, many DSDP/ODP sites indicate that extreme 13C-depletion of methane ΣCO2 occurs within the uppermost methanogenic zone continental rise sediments. We infer 13C-depleted is generated near top when carbon ΣCO2, produced by microbially-mediated anaerobic oxidation, recycled back to through CO2 reduction. Interstitial water gas samples were in 27 cores, 16 which penetrated sulfate reduction into methane-bearing sediments Ridge. Isotopic measurements (δ13CCH4, δ13CCO2, δDCH4, δDH2O) this microbial origin, Methane form two distinct isotopic pools. (1) a seafloor seep site shows mean δ13CCH4 value − 69 ± 2%., mirroring values found at ≥ 160 mbsf nearby DSDP site. (2) Twenty, areally-separated (sample depth, 10 25 mbsf) have ranging −85 −103%., δ13CCO2 as negative −48%.. The very low δ13C pools highlight importance cycling sulfate-methane boundary.