The runoff dependence of fluxes and the variation in relative mobility is less in old rocks than in young ones. In old rocks the number of saturated minerals with respect to soil solutions has decreased because of lesser amount of soluble basaltic glass and an increased vegetative cover on old rocks. The saturation state of basaltic minerals is the most important variable for the dissolution and precipitation rate of minerals during weathering in southwest Iceland and is dictated by the pH of the weathering solutions. The overall rate of chemical denudation rate in southwest Iceland is independent of vegetative cover. However, fluxes of Ca, Mg, and Sr increase with increasing vegetative cover at constant runoff.
Glacial cover slows down the overall chemical denudation rates in southwest Iceland.
It increases the probability of high pH weathering solutions by excluding direct and indirect routes for the CO 2 from the atmosphere to the weathering site and by continuously exposing fresh rocks to the incoming solutions. Thus, the relative mobility and fluxes of Ca and Mg slow down during glacial cover and therefore retard the permanent long-term consumption of atmospheric CO 2 . Transient consumption of atmospheric CO 2 by chemical weathering in southwest Iceland is greater than CO 2 degassing from the Icelandic mantle plume. The relative mobility of the least mobile elements during weathering in southwest Iceland is similar to that observed elsewhere in the world under remarkably variable climatic conditions. Icelandic precipitation shows a normal distribution around a mean pH of 5.4.