TY - JOUR
T1 - The δ13C of biogenic methane in marine sediments
T2 - The influence of C(org) deposition rate
AU - Blair, Neal
N1 - Funding Information:
Many thanks to Chris Martens, Jeff Chanton, Marc Alperin, Dan Albert, Cheryl Kelley, Sue Boehme, Bob Aller and many others for their helpful discussions, field assistance and data, without which this study would not have been possible. Special thanks go to George Claypool for pointing out the importance of carbonate precipitation to this problem. This study was supported by grants from NASA (NAGW-838), NSF (OCE-8812907, OCE-9115709, OCE-9301793) and the NOAA National Undersea Research Program at Wilmington, NC.
PY - 1998/10/26
Y1 - 1998/10/26
N2 - The δ13C of biogenic methane produced in marine sediments ranges from - 110 to - 55‰. The isotopic composition of the methane (δ13C(CH)4) is constrained by the fraction of metabolized organic carbon converted to CH4. The flux of labile organic carbon into the seabed (J(MOC)) and the availability of oxidants (A(OX)), such as O2 and SO4(=), dictate that fraction, i.e., proportionately more methane should be produced as the ratio J(MOC)/A(OX) increases. Chemical, physical (e.g., sediment resuspension) and biological (bioturbation and bioirrigation) processes determine A(OX). Given that δ13C(CH)4 is always less than δ13C of the metabolizable organic carbon, δ13C(CH)4 should increase when J(MOC) and the portion of metabolized carbon converted to methane increase. A positive linear correlation (r2 = 0.92) is observed between δ13C(CH)4 and J(MOC) for a database containing four continental margin sites. When the pore water sulfate gradient (ΔSO4=/Δdepth) is used as a surrogate for J(MOC), the data set is extended to 15 locations spanning all latitudes. A linear relationship between the sulfate gradient and δ13C(CH)4 (r2 = 0.98) for shelf/slope environments suggests that either J(MOC) or J(MOC)/A(OX) is the master variable that controls the 13C/12C content of the biogenic methane. Carbonate precipitation and/or a methanogenic back reaction may obscure the correlation in deep-sea sediments. Evidence for the relationship between δ13C(CH)4 and J(MOC) appears to be preserved in Miocene-age dolomitic deposits.
AB - The δ13C of biogenic methane produced in marine sediments ranges from - 110 to - 55‰. The isotopic composition of the methane (δ13C(CH)4) is constrained by the fraction of metabolized organic carbon converted to CH4. The flux of labile organic carbon into the seabed (J(MOC)) and the availability of oxidants (A(OX)), such as O2 and SO4(=), dictate that fraction, i.e., proportionately more methane should be produced as the ratio J(MOC)/A(OX) increases. Chemical, physical (e.g., sediment resuspension) and biological (bioturbation and bioirrigation) processes determine A(OX). Given that δ13C(CH)4 is always less than δ13C of the metabolizable organic carbon, δ13C(CH)4 should increase when J(MOC) and the portion of metabolized carbon converted to methane increase. A positive linear correlation (r2 = 0.92) is observed between δ13C(CH)4 and J(MOC) for a database containing four continental margin sites. When the pore water sulfate gradient (ΔSO4=/Δdepth) is used as a surrogate for J(MOC), the data set is extended to 15 locations spanning all latitudes. A linear relationship between the sulfate gradient and δ13C(CH)4 (r2 = 0.98) for shelf/slope environments suggests that either J(MOC) or J(MOC)/A(OX) is the master variable that controls the 13C/12C content of the biogenic methane. Carbonate precipitation and/or a methanogenic back reaction may obscure the correlation in deep-sea sediments. Evidence for the relationship between δ13C(CH)4 and J(MOC) appears to be preserved in Miocene-age dolomitic deposits.
KW - Biogenic methane
KW - Marine sediments
KW - δC
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U2 - 10.1016/S0009-2541(98)00102-8
DO - 10.1016/S0009-2541(98)00102-8
M3 - Article
AN - SCOPUS:0032456494
VL - 152
SP - 139
EP - 150
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
IS - 1-2
ER -
