Impacts without Impact: Climatic Stability Across the Late Eocene Impact Horizons

There are approximately 200 known impact craters on Earth, yet the extent to which large extraterrestrial impacts influence climate and life remains uncertain. In this talk, we examine two major impact events that occurred less than 25,000 years apart in the late Eocene, forming the Popigai (northern Siberia) and Chesapeake Bay (eastern North America) structures, the largest known impacts of the Cenozoic era. To evaluate potential palaeoceanographic changes associated with these events, we conducted high resolution (~11 kyr) multispecies planktonic and benthic foraminiferal oxygen (δ18O) and carbon (δ13C) stable isotope records spanning ~360 kyr (35.85–35.49 Ma) from Deep Sea Drilling Project (DSDP) Site 94 in the Gulf of Mexico. This study is the first to apply both planktonic and benthic foraminiferal stable isotopes, building upon earlier benthic and bulk carbonate isotope work. No palaeoclimatic anomalies or δ¹³C excursions are observed across the impact horizons. However, ~100 kyr prior to the impacts (at ~35.75 Ma), the records show a 0.75‰ negative δ¹⁸O shift in planktonic foraminifera alongside a 0.25‰ positive shift in benthic foraminifera, indicating a ~2 °C surface ocean warming and ~1 °C deep water cooling. Importantly, this signal predates the impact events and is not temporally aligned with the impact horizons. Thus, despite the close succession of two large extraterrestrial impacts, within a short space of time (~25 kyr), the results suggest that the palaeoclimatic response was insignificant.