Carbon dioxide in the atmosphere: evidence from Cenozoic and Mesozoic paleosls

Abstract

A diffusion-reaction model for the isotopic composition of soil CO2 and soil carbonate is evaluated. It shows which variables are important under different conditions and shows that under certain circumstances the carbon isotopic composition of soil carbonate can be used to estimate P(CO2) of the atmosphere from late Paleozoic to the present. Preliminary results suggest that P(CO2) was less than about 700 ppmV during the Eocene and since late Miocene because the limiting carbon isotopic composition of soil carbonate was between -11.5 to -12.5 permil relative to PDB. However, early Cretaceous and early Jurassic paleosols have δ13C values between -6.5 and -8.5 permil suggesting that P(CO2) was significantly higher than today, probably on the order of 1500 to 3000 ppmV. -from Author