Inclusion of the weathering of volcanic rocks in the GEOCARBSULF model

The carbon cycle model GEOCARBSULF is extended by dividing the weathering of silicates into volcanic and non-volcanic rocks. The proportion of volcanic weathering is calculated as a function of time from the oceanic record of Sr-87/Sr-86. The volcanic proportion is then used to modify the equations for calculating atmospheric CO2 by the addition of a new non-dimensional volcanic weathering factor. The effect of uplift and physical erosion on weathering is also modified by using only the distribution over time of the abundance of sandstones and shales, and not Sr isotopic data that had been used previously. Results indicate moderate change from GEOCARBSULF in the distribution of atmospheric CO2 over Phanerozoic time. This includes an increased minimum in CO2 during the Late Ordovician, in agreement with the presence of a continental glaciation at that time, and a shift of maximum Mesozoic values from the Jurassic to the Early Cretaceous.