No Evidence for a Large Atmospheric CO2 Spike Across the Cretaceous‐Paleogene Boundary

Abstract

AbstractCurrently, there is only one paleo‐CO2 record from plant macrofossils that has sufficient stratigraphic resolution to potentially capture a transient spike related to rapid carbon release at the Cretaceous‐Paleogene (K‐Pg) boundary. Unfortunately, the associated measurements of stomatal index are off‐calibration, leading to a qualitative interpretation of >2,300‐ppm CO2. Here we reevaluate this record with a paleo‐CO2 proxy based on leaf gas exchange principles. We also test the proxy with three living species grown at 500‐ and 1,000‐ppm CO2, including the nearest living relative of the K‐Pg fern, and find a mean error rate of ~22%, which is comparable to other leading paleo‐CO2 proxies. Our fossils record a ~250‐ppm increase in CO2 across the K‐Pg boundary from ~625 to ~875 ppm. A small CO2 spike associated with the end‐Cretaceous mass extinction is consistent with many temperature records and with carbon cycle modeling of Deccan volcanism and the meteorite impact.