Atmospheric CO2 drawdown during the Emeishan flood basalt volcanism.

The conventional model linking large igneous provinces (LIPs) to atmospheric CO2 concentrations (pCO2) predicts elevated CO2 during volcanic emplacement, leading to biotic crises. However, this generalization requires testing. Here, we reconstruct pCO2 variations throughout the Emeishan LIP emplacement (~260 Ma) using carbon isotopes from chlorophyll-derived compounds. Our high-resolution record reveals that pCO2 declined from ~ 700 ppm to ~ 350 ppm during the early and main flood basalt phases, then increased during subsequent silicic eruptions. This pattern coincides with pre-eruptive crustal uplift driven by mantle plume impingement. We propose that CO2 consumption associated with enhanced erosion and weathering of kilometer-thick Yangtze craton carbonates from regional uplift might have temporarily exceeded the CO2 contribution from magmatic degassing. This is supported by geochemical data indicating that the Emeishan basalt is particularly CO2-poor. Our findings demonstrate that LIP environmental impact begins before the main eruptive phase, highlighting that tectonic-magmatic interactions can produce more complex CO2 patterns than previously recognized. This may explain why some LIPs caused extinctions, whereas others did not.