The Significance of Sulphuric Acid Induced Chemical Weathering on Long Term Fluxes of CO2 Between the Atmosphere-Ocean and Rocks: Evidence From River Chemistry and Carbon Isotopes in the Canadian Cordillera.

It has been proposed that a negative feedback between silicate chemical weathering rates and climate has maintained relatively constant surface temperatures over much of the Earth's history by modulating geological fluxes of CO₂. Attempts to validate this hypothesis have focused on quantifying rates and relative proportions of carbonate versus silicate weathering. Here we demonstrate that quantification of chemical weathering induced by sulphuric acid is also required to accurately calculate the CO₂ flux between the atmosphere-ocean and geological reservoirs. Carbonic acid is formed by the dissolution of CO₂ in water. Sulphuric acid is formed by the chemical weathering of sulphide minerals. Silicate dissolution by carbonic acid causes a net transfer of CO₂ to the geological reservoir. Carbonate dissolution by carbonic acid causes no net transfer of CO₂ between the two reservoirs over geological timescales (>100,000 y). Silicate weathering by sulphuric acid does not involve carbon. However, importantly carbonate dissolution by sulphuric acid causes a net transfer of CO₂ from the geological reservoir to the atmosphere-ocean reservoir. River chemistry and isotopic data from major drainages in the Canadian Cordillera, including the Fraser, Skeena and Nass rivers are used to calculate weathering rates of silicate, carbonate, and sulphide minerals and the related CO₂ fluxes for the different geomorphological regions of the Canadian Cordillera. The magnitude of the CO₂ flux due to carbonate dissolution by sulphuric acid is shown to be highly significant and therefore should be included in carbon balance models.