Dear  David,

You can find isotope composition and concentrations of atmospheric CO2  in
a recent paper by
Fung et al. 1997 Global Biogeochemical cycles, vol 11, no4, p.507 with also
plenty of references.

Stefano


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Dr. Stefano Bernasconi
Geologisches Institut
ETH-Zentrum
CH-8092 Zuerich
Switzerland
Tel. ..41-1-632 3693
fax:  ..41-1-632 1080
e-mail: [log in to unmask]
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