Sulfur and oxygen isotope ratios constrain riverine sulfate sources and terrestrial pyrite oxidation

Abstract

Pyrite oxidation, coupled with carbonate weathering, can be a source of carbon dioxide (CO2) in the atmosphere over geological timescales. However, this source of CO2 is an important but not entirely understood component of the long-term carbon cycle. The exact identification of the riverine sulfate sources and terrestrial pyrite weathering flux is crucial for a quantitative understanding of this source, but it still faces great challenges. Sulfur and oxygen isotope ratios are widely used to constrain sulfate sources. Here, we reviewed the effect of pyrite oxidation on the carbon cycle and synthesized sulfur isotope and oxygen isotope data for global rivers. We also figured out the fluxes of riverine sulfate caused by pyrite oxidation in various rivers around the world using a Bayesian model that is based on the sulfur and oxygen isotope ratios in riverine sulfates and local end elements. The highest pyrite-derived sulfate fluxes were found in the Mississippi River (198.3 ± 37.8 Gmol SO42-year-1). Higher pyrite oxidation rates occurred in areas with higher runoff rates, and global climate change may have also affected pyrite oxidation rates. This may assist in re-evaluating the role of chemical weathering on the carbon cycle and improve the theory of the carbon cycle.