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Science 16 December 1988:
Vol. 242. no. 4885, pp. 1535 - 1539
DOI: 10.1126/science.242.4885.1535
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Articles

The Isotopic Composition of Methane in Polar Ice Cores

H. Craig 1, C. C. Chou 1, J. A. Welhan 1, C. M. Stevens 2, and A. Engelkemeir 3

1 Isotope Laboratory, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093
2 Chemistry Division, Argonne National Laboratory, Argonne, IL 60439
3 Chemical Technology Division, Argonne National Laboratory, Argonne, IL 60439

Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that (i) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (ii) that the carbon-13 to carbon-12 ratio of atmospheric CH4 in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent 13CH4 enrichment, although other factors may also contribute.

Submitted on August 11, 1988
Accepted on October 25, 1988


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Unexpected Changes to the Global Methane Budget over the Past 2000 Years.
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Ice-core record of atmospheric methane changes: relevance to climatic changes and possible gas hydrate sources.
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Biomass Burning in the Tropics: Impact on Atmospheric Chemistry and Biogeochemical Cycles.
P. J. Crutzen, P. J. Crutzen, and M. O. Andreae (1990)
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Gravitational Separation of Gases and Isotopes in Polar Ice Caps.
H. Craig, H. Craig, Y. Horibe, and T. Sowers (1988)
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