Ecosystem controlled soil-rock pCO2 and carbonate weathering – Constraints by temperature and soil water content

International audienceCarbonate dissolution in soil-groundwater systems depends dominantly on pH, temperature and the saturation state of the solution with respect to abundant minerals. The pH of the solution is, in general, controlled by partial pressure of CO2 (pCO(2)) produced by ecosystem respiration, which is controlled by temperature and water availability. In order to better understand the control of land temperature on carbonate weathering, a database of published spring water hydrogeochemistry was built and analysed. Assuming that spring water is in equilibrium with the soil-water-rock-atmosphere, the soil pCO(2) can be back-calculated. Based on a database of spring water chemistry, the average soil-rock CO2 was calculated by an inverse model framework and a strong relationship with temperature was observed. The identified relationship suggests a temperature control on carbonate weathering as a result of variations in soil-rock pCO(2), which is itself controlled by ecosystem respiration processes. The findings are relevant for global scale analysis of carbonate weathering and carbon fluxes to the ocean, because concentration of weathering products from the soil-rock-system into the river system in humid, high temperature regions, are suggested to be larger than in low temperature regions. Furthermore, results suggest that, in specific spring samples, the hydrochemical evolution of rain water percolating through the soil-rock complex can best be described by an open system with pCO(2) controlled by the ecosystem. Abundance of evaporites and pyrite sources influence significantly the chemistry of spring water and corrections must be taken into account in order to implement the inverse model framework presented in this study. Annual surface temperature and soil water content were identified as suitable variables to develop the parameterization of soil-rock pCO(2), mechanistically consistent with soil respiration rate findings