Effects of carbonate minerals and exogenous acids on carbon flux from the chemical weathering of granite and basalt

The chemical weathering of silicate rocks can yield bicarbonate which is transported via rivers to the ocean, followed by the deposition of carbonate, acting as a carbon sink on long time scales. The dissolution of carbonate minerals and the participation of exogenous acids (e.g., sulfuric acid and nitric acid) also affect the chemical weathering process. However, their effects have rarely been quantified at the global scale. Here, based on a compilation of time series datasets of hydro-chemistry samples from 3573 monitoring sites and high-resolution hydro-meteorological datasets, we quantified the effects of carbonate minerals and exogenous acids on the carbon fluxes from the chemical weathering of granite and basalt. The calculated true carbon fluxes of the chemical weathering of granite and basalt were approximately 28.72 Tg C/yr and 30.42 Tg C/yr on the global grid scale. Although the effects of exogenous acids to the true carbon fluxes of the chemical weathering from granite and basalt were similar, corresponding to 30% and 28% of the estimated cation fluxes, respectively, the effect of carbonate minerals on the chemical weathering of granite was approximately twice the effect on the chemical weathering of basalt. These discrepancies were caused by the differences in the chemical weathering characteristics and the laws that integrated the different effects of basalt and granite. Our results address the roles of carbonate minerals and exogenous acids in the global carbon cycle and their link to CO2 consumption via the chemical weathering of silicate rocks.