CHARCOAL EVIDENCE THAT RISING ATMOSPHERIC OXYGEN TERMINATED EARLY JURASSIC OCEAN ANOXIA

Oceanic Anoxic Events (OAEs) represent periods in Earth’s history of major disruption to the global carbon cycle. During an OAE organic carbon burial rates increase due to abundant primary productivity within surface waters, leading to anoxic bottom waters and enhanced organic preservation. Numerical models predict that increased organic carbon burial across an OAE could drive a rise in atmospheric oxygen which may be capable of ultimately terminating ocean anoxia after ~1 million years. However, such model estimates remain untested. Wildfire is highly responsive to changes in atmospheric oxygen therefore we would anticipate that fire activity should vary across an OAE. Here we test this hypothesis by tracing variations in the abundance of fossil charcoal across the Toarcian OAE (T-OAE), occurring ~183 Ma. Our results reveal a sustained ~800 kyr enhancement of fire activity beginning ~1 Myr after the onset of the T-OAE and which peaks during its termination. We hypothesize that this major enhancement of fire, was primarily driven by increased atmospheric oxygen and therefore provides the first fossil based evidence suggesting OAEs are terminated by fire-feedbacks to rising atmospheric oxygen.