The Paleozoic to Mesozoic carbon cycle revisited: The carbon isotopic composition of terrestrial organic matter

[1] Two thousand one hundred forty-eight carbon isotope values for terrestrial organic matter ( plant fossils, coal, bulk terrestrial organic matter) provide a proxy record for temporal changes in the global carbon cycle. delta(13)C(TOM), delta(13)C(carb), and delta(13)C(CO2) allow a full evaluation of carbon transfer in the atmosphere-ocean system as well as between the marine and the terrestrial realm. The temporal evolution of delta(13)C(TOM) parallels respective data sets from marine carbonate carbon, thus reflecting the linkage between both reservoirs via atmospheric carbon dioxide. On the basis of a comparison between measured and predicted isotope records for delta(13)C(TOM), changes in the carbon isotopic fractionation associated with plant metabolism are discernible. This contradicts the notion of an invariable carbon isotopic fractionation associated with C-3 plant metabolism. In light of results from current plant growth experiments, these changes are viewed as dependent on the atmospheric O-2/CO2. Hence delta(13)C(TOM) might serve as a proxy signal for atmospheric composition.