NOAA/WDS Paleoclimatology - Paleo-pCO2 Database Early Cenozoic Stomata CO2 Data

Currently, 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.