GEOCARB III A REVISED MODEL OF ATMOSPHERIC CO2 OVER.pdfVIP

[American Journal of Science, Vol. 301, February, 2001, P. 182–204] GEOCARB III: A REVISED MODEL OF ATMOSPHERIC CO OVER 2 PHANEROZOIC TIME ROBERT A. BERNER and ZAVARETH KOTHAVALA Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520-8109 ABSTRACT. Revision of the GEOCARB model (Berner, 1991, 1994) for paleolevels of atmospheric CO , has been made with emphasis on factors affecting CO uptake by 2 2 continental weathering. This includes: (1) new GCM (general circulation model) results for the dependence of global mean surface temperature and runoff on CO , 2 for both glaciated and non-glaciated periods, coupled with new results for the temperature response to changes in solar radiation; (2) demonstration that values for the weathering-uplift factor fR (t) based on Sr isotopes as was done in GEOCARB II are in general agreement with independent values calculated from the abundance of terrigenous sediments as a measure of global physical erosion rate over Phanerozoic time; (3) more accurate estimates of the timing and the quantitative effects on Ca-Mg silicate weathering of the rise of large vascular plants on the continents during the Devonian; (4) inclusion of the effects of changes in paleogeography alone (constant CO2 and solar radiation) on global mean land surface temperature as it affects the rate of weathering; (5) consideration of the effects of volcanic weathering, both in subduction zones