GEOCARB II: a revised model of atmospheric CO2 over Phanerozoic time

Abstract

Revisions of the parameters in the model of Berner (1991) (henceforth GEOCARB I) for the long term geochemical carbon cycle have been made. Results include the following: 1) increase in the solar constant over the past 570 my has brought about a gradual drop in atmospheric CO2 from values much higher during the early Paleozoic than today; 2) high CO2 values during the Mesozoic and a decrease in CO2 during the Cenozoic are due largely to low Mesozoic relief and Cenozoic mountain uplift combined with decreasing metamorphic/volcanic degassing of CO2 during the Cenozoic; 3) variable degassing, due to changes in seafloor spreading rate, was not a major control on atmospheric CO2 during the Paleozoic; 4) calculated Phanerozoic CO2 is sensitive to the proportion of carbonate deposition in shallow water versus the deep sea as this affects the probability that the carbonate will be deeply buried and thermally degassed. Over Phanerozoic time a major control on global climate has been the CO2 greenhouse effect, and changes in CO2 have been a consequence of a combination of geological, biological, and astronomical factors. -from Author