Rock organic carbon oxidation CO2 release offsets silicate weathering sink

Mountain uplift and erosion have regulated the balance of carbon between Earth's interior and atmosphere, where prior focus has been placed on the role of silicate mineral weathering in CO2 drawdown and its contribution to the stability of Earth's climate in a habitable state1-5. However, weathering can also release CO2 as rock organic carbon (OCpetro) is oxidized at the near surface6,7; this important geological CO2 flux has remained poorly constrained3,8. We use the trace element rhenium in combination with a spatial extrapolation model to quantify this flux across global river catchments3,9. We find a CO2 release of Formula: see text megatons of carbon annually from weathering of OCpetro in near-surface rocks, rivalling or even exceeding the CO2 drawdown by silicate weathering at the global scale10. Hotspots of CO2 release are found in mountain ranges with high uplift rates exposing fine-grained sedimentary rock, such as the eastern Himalayas, the Rocky Mountains and the Andes. Our results demonstrate that OCpetro is far from inert and causes weathering in regions to be net sources or sinks of CO2. This raises questions, not yet fully studied, as to how erosion and weathering drive the long-term carbon cycle and contribute to the fine balance of carbon fluxes between the atmosphere, biosphere and lithosphere2,11.