Carbon Release from Ferrar Large Igneous Province Sustained the Elevated pCO2 Level in the Toarcian Oceanic Anoxic Event

The Toarcian oceanic anoxic event (T-OAE) represents one of the most severe hyperthermal events of the Mesozoic, characterized by rapid global warming, widespread marine anoxia and a prominent negative carbon isotope excursion (CIE). However, the dynamic evolution of carbon sources throughout this event and the role of the Karoo-Ferrar large igneous province (LIP) during the CIE recovery phase remain poorly constrained. Here we present a continuous pCO2 record throughout this period based on phytane carbon isotope data from multiple sections, and reconstruct the carbon emission scenario using iLOSCAR model. We find that pCO2 rose from 450 ppm to ~800 ppm. During the CIE recovery phase and even after the event, pCO2 did not return to pre-CIE background values but remained elevated. Model simulations reveal a three-stage evolutionary pattern of carbon sources. At the onset of the T-OAE, biogenic methane release drove the rapid negative CIE and the surge in pCO2. During the CIE recovery phase, thermogenic carbon released by the Ferrar LIP counteracted the enhanced carbon sink caused by chemical weathering and organic carbon burial, maintaining elevated pCO2 levels. After the CIE, the primary source of carbon release from the Ferrar LIP shifted to predominantly mantle-derived degassing, which sustained high pCO2 levels without significantly affecting the isotopic composition of the surface carbon reservoir. These findings demonstrate that the Ferrar LIP acted as a persistent driver throughout the latter intervals of the T-OAE, profoundly influencing the trajectory of pCO2 evolution and delaying environmental recovery.