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The isotopic composition of methane in polar ice coresAir 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: (1) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (2) 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 C-13H4 enrichment, although other factors may also contribute.
Document ID
19890034403
Document Type
Reprint (Version printed in journal)
Authors
Craig, H. (California Univ. La Jolla, CA, United States)
Chou, C. C. (California Univ. La Jolla, CA, United States)
Welhan, J. A. (California, University La Jolla, United States)
Stevens, C. M. (California Univ. La Jolla, CA, United States)
Engelkemeir, A. (Argonne National Laboratory IL, United States)
Date Acquired
August 14, 2013
Publication Date
December 16, 1988
Publication Information
Publication: Science
Volume: 242
ISSN: 0036-8075
Subject Category
GEOPHYSICS
Funding Number(s)
CONTRACT_GRANT: NSF DPP-82-18040
CONTRACT_GRANT: W-31-109-ENG-38
CONTRACT_GRANT: NSF DPP-85-21486
CONTRACT_GRANT: NSF ATM-82-17819
CONTRACT_GRANT: NASA ORDER W-16188
Distribution Limits
Public
Copyright
Other