Evaluating global soil weathering data through a solute production framework

The silicate weathering feedback, thought to be Earth’s primary long-term climate regulator, is hypothesized to be most active in rapidly uplifting mountainous settings, dissolving freshly-exposed silicate rocks to draw down elevated atmospheric pCO2 concentrations. Silicate weathering rates are influenced by the interaction of many environmental factors, including temperature, lithology, hydrology, vegetation, and erosion, but disentangling the influence of each on a site-by-site and global basis yields conflicting conclusions and therefore remains an active area of research. Silicate weathering rates are estimated from both soil and dissolved solutes; however, competing theoretical frameworks, centered around solid-phase and aqueous-phase geochemical data, have yet to be reconciled. In this study, we assessed the influence of erosion, lithology, and hydrology on global weathering and analyzed weathering rates from soils through the lens of a solute production weathering framework. To examine the correlation between environmental factors and silicate weathering, we expanded existing global soil compilations to include additional published soil weathering rates and extracted site-specific environmental parameters from global reanalysis, satellite remote-sensed, and regional meteorological raster datasets. To reduce variability in weathering due to mineralogy, we calculated sodium fluxes as a proxy for Na-plagioclase weathering, resulting in a strengthened relationship between mineral-specific weathering fluxes and erosion. Normalizing for mean annual precipitation, we observe potential hydrologic controls on fluid residence time limiting solute production, indicating that all soils in the weathering compilation classify as kinetically limited according to the solute production framework. To assess how soil weathering rates align with conceptions of solute generation, we superimpose soil data onto the Maher and Chamberlain (2014) solute production model, testing the fit of model scenarios against soil weathering trends. We find that scenarios including a flow path length dependence on regolith thickness, controlled by erosion and precipitation rates, best capture denudation and weathering trends, yielding the highest predictive power in capturing modeled Na weathering concentrations. Although a shortage of weathering rate data in areas with high denudation rates limits our ability to assess the best fit model scenario with certainty, our analysis highlights the coupled role of hydrology and erosion as primary drivers of silicate weathering in soils globally.