Addendum to Inclusion of the weathering of volcanic rocks in the GEOCARBSULF model (vol 306, pg 295-302, 2006)

In the paper by Berner (2006a) the compiled data presented by Dessert and others (2001), for different values of the relative weathering rates of basalts versus granites, was missed. (The term granite is used here to refer to all granitoid rocks including gneisses.) It is the primary purpose of this paper to see how usage of different values for the intrinsic weatherability ratio of basalt/granite affects recalculation of the concentration of atmospheric CO2 and values for the fraction of silicate weathering contributed by volcanics (Xvolc). (Intrinsic weatherability refers to weathering rate occurring under the same conditions of climate, exposure, relief, et cetera.) In addition, the paper by Berner (2006a) probably underestimated the value for the present (pre-industrial) rate of Ca-Mg exchange via basalt-seawater reaction to be 0.75 X 10(18) mol/my. This value is improbable in that it produces a Sr/Ca ratio that is about 4 times higher than that actually found in most basalts and is about 6 times lower than the value calculated for basalt-seawater exchange based on river-ocean mass balance (Berner and Berner, 1996). Thus, I also consider here the effect on Xvolc and CO2 of different basalt-seawater reaction rates.