Ruminant methane delta(13C/12C) values: relation to atmospheric methane

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Science  06 Mar 1981:
Vol. 211, Issue 4486, pp. 1044-1046
DOI: 10.1126/science.7466376


The delta(13C/12C)--values of methane produced by fistulated steers, dairy cattle, and wethers, and dairy and beef cattle herds show a bimodal distribution that appears to be correlated with the plant type (C3 or C4, that is, producing either a three- or a four-carbon acid in the first step of photosynthesis) consumed by the animals. These results indicate that cattle and sheep, on a global basis, release methane with an average delta(13C/12C) value of -60 and -63 per mil, respectively. Together they are a source of atmospheric methane whose delta(13C/12C) is similar to published values for marsh gas and cannot explain the 20 per mil higher values for atmospheric methane.