Charcoal evidence that rising atmospheric oxygen terminated Early Jurassic ocean anoxia

The Toarcian Oceanic Anoxic Event (T-OAE) was characterized by a major disturbance to the global carbon(C)-cycle, and depleted oxygen in Earth’s oceans resulting in marine mass extinction. Numerical models predict that increased organic carbon burial should drive a rise in atmospheric oxygen ( p O 2 ) leading to termination of an OAE after ∼1 Myr. Wildfire is highly responsive to changes in p O 2 implying that fire-activity should vary across OAEs. Here we test this hypothesis by tracing variations in the abundance of fossil charcoal across the T-OAE. We report a sustained ∼800 kyr enhancement of fire-activity beginning ∼1 Myr after the onset of the T-OAE and peaking during its termination. This major enhancement of fire occurred across the timescale of predicted p O 2 variations, and we argue this was primarily driven by increased p O 2 . Our study provides the first fossil-based evidence suggesting that fire-feedbacks to rising p O 2 may have aided in terminating the T-OAE. Numerical models predict that during an oceanic anoxic event (OAE), increased organic carbon burial drives a rise in atmospheric oxygen leading to the event’s termination. Here, the authors present evidence suggesting that the Toarcian OAE was terminated by rising oxygen and associated fire-feedbacks.