Methane carbon isotope fractionation

The carbon isotope fractionation between CO2 and methane and between graphite and methane is a sensitive function of temperature. 

Rather than using the isotopic composition of methane alone James (1983, 1990) and others have demonstrated that carbon isotope fractionations between the hydrocarbon components (particularly propane, iso-butane and normal butane) within a natural gas can be used with distinct advantages to determine maturity, gas-source rock and gas-gas correlations. With increasing molecular weight, from Ci to C4, a enrichment is observed which approaches the carbon isotope composition of the source. 

Abelson PH, Hoering TC (1961) Carbon isotope fractionation in formation of amino acids by photo synthetic organisms, Proc Natl Acad Sci U S A 47 623 Abrajano TA, Sturchio NB, Bohlke JH, Lyon GJ, Poreda RJ, Stevens MJ (1988) Methane -hydrogen gas seeps Zambales ophioUte, PhUlippines deep or shallow origin. Chem Geol 71 211-222... 

Carbonates are generated in all of the zones, but they are consumed only below the third stage. After the depletion of more than 80% of the sulfate, the components of XCO2 become oxidants, leading to the production of methane. It is possible to distinguish between the CO2 produced and the CO2 consumed, determining the extent of carbon isotopic fractionation, particularly associated with the methane production in stage four. 

Whereas isotope selectivity during bacterial oxidation of CH has been measured (8,9), there are few data relevant to TSR. Consequently, laboratory experiments were conducted to measure carbon isotope fractionation accompanying the oxidation of methane, ethane, and propane. 

Barker J. F. and Fritz P. (1981) Carbon isotope fractionation during microbial methane oxidation. Nature 293, 289-291. 

Silverman M. P. and Oyama V. 1. (1968) Automatic apparatus for sampling and preparing gases for mass spectral studies of carbon isotope fractionation during methane metabolism. Anal. Chem. 40, 1833-1877. 

The nonbiological fractionation of carbon isotopes. Horita (2005) has shown in a recent review that abiotic reactions can also produce carbon isotope fractionations and that these fractionations can be as large as those driven by biogenic processes. Particularly important is the production of methane (Sherwood Lollar et al., 2006). In the vicinity of ocean-floor hydrothermal vents, ultramafic rocks containing olivine may react with seawater, and dissolved bicarbonate can become converted to methane. In the presence of a Fe-Ni alloy catalyst carbon isotopes are fractionated as much as 50-60%o at 200° C and 35 to 40%o at 300° C (Horita. Berndt, 1999). This degree of fractionation is very similar to that produced by methanogenic bacteria. 

Rosenfeld, W.D. Silverman, S.R. (1959) Carbon isotope fractionation in bacterial production of methane. Science, 130, 1658-1659. 

Blair N, Leu A, Munoz E, Olsen J, Kwong E, DesMarais D (1985) Carbon isotopic fractionation in heterotrophic nticrobial metabolism. Appl Environ Microbiol 50 996-1001 Boetius A, Ravenschlag K, Schubert CJ, Rickert D, Widdel F, Gieseke A, Amarm R,Jorgensen BB, Witte U, Pfannkuche O (2000) A marine microbial consortium apparently mediating anaerobic oxidation of methane. Nature 407 623-626... 

Elvert M, Suess E, Whiticar MJ (1999) Anaerobic methane oxidation associated with marine gas hydrates Superlight C-isotopes from saturated and unsaturated C20 and C25 irregular isoprenoids. Naturwiss 86 Erez J, Bouevitch A, Kaplan A (1998) Carbon isotope fractionation by photosynthetic aquatic mircroorganisms experiments with Synechococcus PCC7942, and a simple carbon flux model. Canadian J Botany 76 1109-1118... 

Zhang TW, Krooss BM (2001) Experimental investigation on the carbon isotope fractionation of methane during gas migration by diffusion through sedimentary rocks at elevated temperatme and pressure. Geochim Cosmochim Acta 65 2723-2742... 

Steuber T, Buhl D (2006) Calcium-isotope fractionation in selected modern and ancient marine carbonates. Geochim Cosmochim Acta 70 5507-5521 Stevens CM (1988) Atmospheric methane. Chem Geol 71 11-21... 

Alperin M. J., Reeburgh W. S., and Whiticar M. J. (1988) Carbon and hydrogen isotope fractionation resulting from anaerobic methane oxidation. Global Biogeochem. Cycles 2, 279-288. 

I. 0). The isotopic composition of alkanes and of other classes of compounds can also be used as a general source input indicator. Isotopic fractionation resulting from the metabolic pathways involved in the synthesis of biologically produced compounds, when preserved in a dlagenetlc product, is frequently used to differentiate between terrestrial and aquatic sources. Hydrogen and carbon isotopic compositions of biogenic methanes from shallow aquatic environments is discussed in a later chapter of this volume (R. A. Burke and W. M. Sackett). The applicability of carbon isotopic data to tracing the source of deep-sea Mesozoic sediments is discussed by R.M. Joyce and E. S. Van Vleet. 

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