RELATION BETWEEN SOIL AGE AND SILICATE WEATHERING RATES DETERMINED FROM THE CHEMICAL EVOLUTION OF A GLACIAL CHRONOSEQUENCE

Long-term weathering rates (R(LT)) were determined from base cation depletion in soil profiles developed on six granitic glacial moraines varying in age from 0.4 to greater than or equal to 297 ha in the Wind River Mountains, Wyoming. Weathering rates were found to decrease with soil age (t) according to the power-law equation R(LT) = 215 . t((-0.71)), where R(LT) is in meg . m(-2) . yr(-1), and t is in ha. Comparable data from the literature are consistent with this function, and it is similar to power-law, equations describing changes in laboratory weathering rates with time. On the basis of our study, we predict that for a catchment unaffected by anthropogenic inputs and in a steady state with respect to the organic and cation exchange pools, R(LT) should be higher than present-day weathering rates derived from stream fluxes (R(PD)) by a factor of about 3.4.