The Chicxulub Impact Event and Atmospheric Sulfur

[Life]

Baby, it's cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous

Abstract

Sixty-six million years ago, the end-Cretaceous mass extinction ended the reign of the dinosaurs. Flood basalt eruptions and an asteroid impact are widely discussed causes, yet their contributions remain debated. Modeling the environmental changes after the Chicxulub impact can shed light on this question. Existing studies, however, focused on the effect of dust or used one-dimensional, noncoupled atmosphere models. Here we explore the longer-lasting cooling due to sulfate aerosols using a coupled climate model. Depending on aerosol stratospheric residence time, global annual mean surface air temperature decreased by at least 26°C, with 3 to 16 years subfreezing temperatures and a recovery time larger than 30 years. The surface cooling triggered vigorous ocean mixing which could have resulted in a plankton bloom due to upwelling of nutrients. These dramatic environmental changes suggest a pivotal role of the impact in the end-Cretaceous extinction.

Key Points

• We use a coupled climate model to investigate the effects of sulfate aerosols and carbon dioxide from the Chicxulub impact
  
• We find severe cooling suggesting a major role of the impact in the mass extinction event
• Surface cooling of the ocean results in vigorous mixing which could have caused a plankton bloom

Citation: Brugger, J., Feulner, G., & Petri, S. (2017). Baby, it's cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous. Geophysical Research Letters, 44(1), 419-427.

Link: agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL072241

[Life]

Massive perturbations to atmospheric sulfur in the aftermath of the Chicxulub impact

Significance

Sulfur isotopes confirm a key role for atmospheric sulfur gases in climatic cooling, mass extinction, and the demise of dinosaurs and other global biota after the Chicxulub bolide impact at the Cretaceous–Paleogene boundary. The sulfur isotope anomalies are confined to beds containing ejecta and, in the immediately overlying sediments, are temporally unrelated to known episodes of volcanism that also bracket this event, further addressing the controversial role of the Deccan Traps in the extinction.

Abstract

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.

Citation: Junium, C. K., Zerkle, A. L., Witts, J. D., Ivany, L. C., Yancey, T. E., Liu, C., & Claire, M. W. (2022). Massive perturbations to atmospheric sulfur in the aftermath of the Chicxulub impact. Proceedings of the National Academy of Sciences, 119(14), e2119194119.

Link: www.pnas.org/doi/full/10.1073/pnas.2119194119#executive-summary-abstract