Recent trends in the 13C/12C ratio of atmospheric carbon dioxide

THE 13C/12C ratio of atmospheric carbon dioxide has decreased by approximately 0.6‰ over 22 yr according to new direct measurements reported here. Our results offer a way of establishing whether 13C/12C ratios of tree rings1–6 are representative of atmospheric 13CO2 variations. We have carried out both isotopic (at Groningen) and concentration (at La Jolla) measurements of atmospheric CO2 on air samples obtained during 1977 and 1978 at three widely spaced locations: La Jolla, California (33°N, 117°W), Fanning Island (4°N, 159°W) and the South Pole. Sampling, instrumental, and analytical procedures closely matched a similar study carried out 22 yr earlier by Keeling7,8.

[1]  R. Weiss,et al.  Production of atmospheric nitrous oxide by combustion , 1976 .

[2]  C. D. Keeling,et al.  The effects of atmospheric NO2 on the measured isotopic composition of atmospheric CO2 , 1963 .

[3]  M. Baxter,et al.  Atmospheric carbon dioxide levels as indicated by the stable isotope record in wood , 1974, Nature.

[4]  H. Oeschger,et al.  A box diffusion model to study the carbon dioxide exchange in nature , 1975 .

[5]  R. Revelle,et al.  Energy and Climate , 1977, Environmental Conservation.

[6]  R. Francey,et al.  Climatic implications of stable carbon isotopes in tree rings , 1976, Nature.

[7]  Charles D. Keeling,et al.  The concentration and isotopic abundances of carbon dioxide in rural and marine air , 1961 .

[8]  S. Rasool.  Chemistry of the lower atmosphere , 1973 .

[9]  Charles D. Keeling,et al.  The concentration and isotopic abundances of atmospheric carbon dioxide in rural areas , 1958 .

[10]  M. Stuiver.  Atmospheric Carbon Dioxide and Carbon Reservoir Changes , 1978, Science.

[11]  Carl Ekdahl,et al.  Atmospheric carbon dioxide variations at the South Pole , 1976 .

[12]  Carl Ekdahl,et al.  Atmospheric carbon dioxide variations at Mauna Loa Observatory, Hawaii , 1976 .

[13]  C. D. Keeling.  The Carbon Dioxide Cycle: Reservoir Models to Depict the Exchange of Atmospheric Carbon Dioxide with the Oceans and Land Plants , 1973 .

[14]  H. Craig.  Isotopic standards for carbon and oxygen and correction factors for mass-spectrometric analysis of carbon dioxide , 1957 .

[15]  H. Freyer,et al.  Dendrochronology and 13C content in atmospheric CO2 , 1974, Nature.