Emission Uncertainties of Soot from an Asteroid Impact at the Cretaceous-Paleogene Mass Extinction Event

An asteroid impact in Chicxulub, Mexico was coincident with the Cretaceous-Paleogene (K-Pg) extinction event (66 Ma). The K-Pg boundary iridium layer contains a large amount of soot, which is consistent with global fires ignited by heating from the reentry of impact debris. A large amount of soot emitted above the tropopause could block the sunlight from reaching the surface and shut down photosynthesis for many months. Concurrently, extreme cooling on land and in the ocean could hasten the extinction of many species. By analyzing proxy data from the fossils of fish and insects, several recent studies reveal that the impact occurred during boreal spring and summer. However, debates about the amount, timing, and duration of soot emissions remain.

Here, we use the Community Earth System Model (CESM) to investigate the effects of seasonal timing and duration of soot emission by emitting soot in either the winter or summer over the course of a day or 2-weeks. We run each simulation for a decade to explore the differences in radiation and surface temperature responses. Our preliminary results show extreme surface light reduction and cooling, regardless of the timing and duration of soot emission. However, the timing and duration of emissions can have regional effects on the severity of the impact winter. Furthermore, these emission differences alter the relative ratio of fine to coarse soot, which can be directly compared with geologic records to constrain soot emission scenarios. In our presentation, we will also explore the potential importance of organic coating on the soot, which can alter the atmospheric residence time of the soot and the severity of the impact winter.