Quote:
Originally Posted by AstralTraveller
For me it is more appropriate to quote the change in the 13C/12C ratio of atmospheric CO2 since I started working in stable isotopes. The ratio has decreased by 0.24 permil (parts per thousand) in that time. The reason the atmosphere is becoming isotopically lighter is that fossil fuel has a much lower 13C content than CO2 from natural sources - principally the ocean.
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Out of interest, what is the typical delta-C of fossil fuels? Rubisco fractionates by about -28 per mil, is that pretty much what you see? Or is it shifted significantly from that? We can use the fractionation in plants to estimate the long-term stomatal condutance (well the Ci/Ca ratio anyway), it would be fascinating if you could do that on geological timescales!