CONSTRAINING EMISSIONS SCENARIOS AT THE CRETACEOUS/PALEOGENE BOUNDARY

The end-Cretaceous mass extinction was marked by the simultaneous emplacement of the Deccan Traps Large Igneous Province and the Chicxulub asteroid impact. Both events resulted in the emission of climate-active volatile gases, which are thought to have caused the demise of non-avian dinosaurs through a combination of ocean acidification, global warming, and cooling on long and short timescales. Key to understanding the kill mechanism of this geologic event is disentangling the timing, duration, and intensity of the emissions, after which we can assess the relative contribution of the volcanism and asteroid impact. Using a parallel Markov Chain Monte Carlo algorithm and the LOSCAR carbon cycle model, we allow the emissions of CO₂ and SO₂ and the export productivity to freely vary over 1.5 million years around the K/Pg boundary. We then compare the model outputs to the proxy values of δ¹⁸O and planktic and benthic δ¹³C, to arrive at an optimal solution. We find export productivity decreases to ~40% of its pre-extinction levels over 500,000 years, and that the CO₂ and SO₂ outputs are highly decoupled, with most outgassing happening after the boundary and no noticeable spike associated with the asteroid impact. This work represents the best guess of the physical and biological changes at the K/Pg using the LOSCAR model and provides a plausible hypothesis for the dinosaur extinction.