CO2 and sulfuric acid controls of weathering and river water composition

Reactions of CO2 with carbonate and silicate minerals in continental sediments and upper part of the crystalline crust produce HCO3− in river and ground waters. H2SO4 formed by the oxidation of pyrite and reacting with carbonates may produce CO2 or HCO3−. The ratio, ψ, of atmospheric or soil CO2 consumed in weathering to HCO3− produced depends on the mix of CO2 and H2SO4, and the proportions of the carbonates and silicates in the source rock. An average sediment has a CO2 uptake potential of ψ = 0.61. The potential increases by inclusion of the crystalline crust in the weathering source rock. A mineral dissolution model for an average river gives ψ = 0.68 to 0.72 that is within the range of ψ = 0.63 to 0.75, reported by other investigators using other methods. These results translate into the CO2 weathering flux of 20 to 24 × 1012mol/yr.