Mass balance of {sup 13}C and {sup 12}C in an organic-rich methane-producing marine sediment
Journal Article
·
· Geochimica et Cosmochimica Acta
- North Carolina State Univ., Raleigh, NC (United States)
- Univ. of North Carolina, Chapel Hill, NC (United States)
The sedimentary budgets of {sup 12}C and {sup 13}C were determined for the well-characterized coastal site of Cape Lookout Bight, North Carolina, USA. Degradation of organic carbon with a {delta}{sup 13}C value of -19.2 {+-} 0.2{per_thousand} proceeds via sulfate reduction and methanogenesis. Neither process detectably alters the {sup 13}C/{sup 12}C composition of the solid phase organic fraction that is ultimately buried. The remineralized carbon ({Sigma}CO{sub 2} plus CH{sub 4}) has an annual mean {delta}{sup 13}C of -18.7 {+-} 2.2{per_thousand}, indicating that the breakdown of solid phase organic material to dissolved intermediates does not discriminate between {sup 13}C and {sup 12}C. The dominant carbon isotope effect expressed during the diagenesis of the organic matter is associated with methanogenesis. Methane produced at this site has a measured annual mean {delta}{sup 13}C value of -58.9 {+-} 1.4{per_thousand}. The {Sigma}CO{sub 2} is enriched in {sup 13}C (-11.0 {+-} 1.2{per_thousand}) because of the preferential synthesis of {sup 12}CH{sub 4}. The relative rate of production of the {Sigma}CO{sub 2} and CH{sub 4}, which is controlled by the depositional flux of metabolizable organic carbon, along with the fractionation factor associated with methanogenesis and the isotopic composition of the source carbon, determine the {sup 13}C/{sup 12}C content of the two diagenetic endproducts. 75 refs., 9 figs., 4 tabs.
- OSTI ID:
- 577438
- Journal Information:
- Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 20 Vol. 60; ISSN 0016-7037; ISSN GCACAK
- Country of Publication:
- United States
- Language:
- English
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