Unstable climate for 50,000 years after Chicxulub impact: evidence from Antarctica

The ~ 66 Ma Cretaceous/Paleogene (K/Pg) boundary coincides with a severe mass extinction widely attributed to the Chicxulub impact and consequent abrupt climatic changes. However, it is unclear how long the subsequent climatic disruptions affected terrestrial and marine environments and what caused them. Here, we present magnesium isotope (δ²⁶Mg) and Chemical Index of Alteration data from an expanded section on Seymour Island, Antarctica, where a new cyclostratigraphic age model provides millennial-scale resolution. Pre-boundary weathering indices, including δ²⁶Mg values, record a stable, mild weathering regime. Post-boundary weathering saw a transition to a substantially variable regime with intervals of intense weathering revealed. This environmental instability persisted for at least 43.89 kyr after impact, and may reflect the climatic influence of Deccan volcanism. Thus, whilst the Chicxulub impact can be directly implicated in mass extinction, the recovery interval was substantially affected by Deccan volcanism.