The role of organic carbon weathering in the Late Ordovician glaciation

Enhanced silicate weathering has been traditionally considered a dominant mechanism for atmospheric carbon dioxide (CO2) drawdown, acting as a negative feedback on climate warming over geological time scales. In contrast, weathering of rock organic carbon (OCpetro) may constitute a positive climate feedback, with enhanced OCpetro oxidation amplifying warming by releasing CO2 to the atmosphere and oceans. However, the influence of CO2 emissions from oxidative weathering on ancient climate events is unclear. Here, we use rhenium isotopes to investigate the role of OCpetro weathering in modulating the global carbon cycle during the Hirnantian glaciation. These data indicate that the weathering intensity of sedimentary rocks was reduced during the glaciation, an observation that is consistent with lower CO2 emissions from the reduced oxidative weathering of OCpetro during this critical interval. Our findings highlight the likely contribution of OCpetro weathering to Earth’s carbon cycle and its role in modulating climate during critical periods of Earth’s history.