¹Christopher K. Junium,²Aubrey L. Zerkle,³James D. Witts,¹Linda C. Ivany,⁴Thomas E. Yancey,⁵Chengjie Liu,²Mark W. Claire
Proceedings of the National Academy of Science of the USA (PNAS) 119 (14) e2119194119 Link to Article [https://doi.org/10.1073/pnas.2119194119]
¹Department of Earth and Environmental Sciences, Syracuse University, Syracuse, NY13244
²School of Earth and Environmental Sciences,Centre for Exoplanet Science, University of St Andrews, StAndrews KY16 9AL, United Kingdom
³School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom
⁴The College of Geosciences, Texas A&MUniversity, College Station, TX 77483
⁵Ellington Geological Services, Houston, TX 77043

Sulfate aerosols have long been implicated as a primary forcing agent of climate change and mass extinction in the aftermath of the end-Cretaceous Chicxulub bolide impact. However, uncertainty remains regarding the quantity, residence time, and degree to which impact-derived sulfur transited the stratosphere, where its climatic impact would have been maximized. Here, we present evidence of mass-independent fractionation of sulfur isotopes (S-MIF) preserved in Chicxulub impact ejecta materials deposited in a marine environment in the Gulf Coastal Plain of North America. The mass anomalous sulfur is present in Cretaceous–Paleogene event deposits but also extends into Early Paleogene sediments. These measurements cannot be explained by mass conservation effects or thermochemical sulfate reduction and therefore require sulfur-bearing gases in an atmosphere substantially different from the modern. Our data cannot discriminate between potential source reaction(s) that produced the S-MIF, but stratospheric photolysis of SO₂ derived from the target rock or carbonyl sulfide produced by biomass burning are the most parsimonious explanations. Given that the ultimate fate of both of these gases is oxidation to sulfate aerosols, our data provide direct evidence for a long hypothesized primary role for sulfate aerosols in the postimpact winter and global mass extinction.