Testing for supply-limited chemical erosion in field measurements of soil production and chemical depletion

Abstract:

Quantifying the controls on chemical erosion rates in eroding landscapes is of wide interest because chemical erosion influences nutrient supply, landscape evolution, soil production, and Earth’s long-term climate. Several field studies have suggested that chemical erosion rates increase in proportion to the rates that minerals are supplied to the regolith, a condition known as supply-limited chemical erosion. This condition, if broadly applicable, implies strong tectonic control of silicate weathering rates and hence Earth’s long-term climate. While it is plausible that chemical erosion rates should scale with supply rates, attempts to test whether chemical erosion rates are in fact supply-limited at any given site are hampered by several difficulties. For instance, the quantities that are most frequently used to test for supply limitation (i.e., rates of chemical erosion and denudation in regolith-based studies, and fluxes of sediment and solutes in river-based studies) are artifactually correlated, which complicates attempts to regress one variable against another. Here we present a statistical method for testing for supply-limited chemical erosion, and we apply this method to a number of published datasets. Our results suggest that many datasets are inadequate for determining whether chemical erosion in regolith is or is not supply-limited, largely because the uncertainties on the regression parameters are large. This in turn suggests that new measurements across a wide range of supply rates are needed to determine the strength of tectonic controls on chemical erosion, and, ultimately, to test hypotheses about feedbacks between surface processes, silicate weathering, and the long-term evolution of Earth’s climate.