A 400 million year carbon isotope record of pedogenic carbonate; implications for paleoatomospheric carbon dioxide

A 400 record of atmospheric carbon dioxide levels has been estimated by applying a COsub 2 paleobarometer to a database of 758 analyses of paleosol (fossil soil) carbonates. This database is a compilation of new data and previously published values from the literature. Many new analyses of Mesozoic paleosols are reported, an era poorly represented in the literature. Results indicate that large fluctuations in atmospheric carbon dioxide levels have occurred over the study interval, ranging from the current level up to ten times the current level. Declining pCOsub 2 levels through the middle Paleozoic culminate in low levels in the Early Permian. An abrupt increase in pCOsub 2 in the Early Permian is followed by a decrease prior to the Permo-Triassic boundary. Carbon dioxide levels increase through the Triassic to approx. 3, 000 ppmV, a level maintained through the Jurassic period. Levels lowered through the Cretaceous, dropping to less than 1, 000 ppmV prior to the Cretaceous-Tertiary boundary. Relatively low levels persisted throughout the Cenozoic, with some evidence of higher levels in the Eocene and Oligocene.