Biogenic methane emissions and carbon cycle perturbations during the Toarcian Oceanic Anoxic Event

The carbon cycle is a one of the fundamental components of the Earth system, regulating long-term climate evolution and ecosystem stability. The Early Jurassic Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) represents one of the most severe global crises of the Mesozoic, characterized by pronounced negative carbon isotope excursions (CIEs), global warming, and widespread declines. Despite decades of study, its underlying mechanisms have remained debated, with particular uncertainty surrounding the nature of the carbon source and the mode of its release. This article presents and interprets recently published results based on a newly developed CHEES model, which explicitly couples sediment–water–atmosphere methane cycling. By integrating high-resolution carbon-isotope, p CO2 , and temperature proxy records and applying Bayesian inversion, the study quantitatively reconstructs carbon release during the T-OAE. The results demonstrate that only scenarios involving biogenic methane release (δ13C of –50‰ to –70‰) can simultaneously reproduce the rapid negative CIE, rising p CO2 , and global temperature increase observed during the event. The inversion further indicates that methane was released in five discrete pulses, each on the order of ~200–1100 Gt C, with a minimum cumulative release of ~4700 Gt C. This resulted in a sharp increase in atmospheric CH4 concentrations from ~0.8×10–6 (volume mixing ratio) to ~10–15×10–6 during the event. These methane pulses closely coincide with two major phases of biodiversity loss, highlighting a central role for methane in driving both climatic perturbations and ecological crises. This work not only resolves long-standing debates but also provides a deep-time analogue for evaluating future methane feedback risks.