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

Abstract

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.

No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From 40Ar/39Ar Dates, Magnetostratigraphy, and Biostratigraphy

“…We can also assess the roles of different initial atmospheric pCO 2 concentrations and equilibrium climate sensitivity values. In the early Paleocene, background pCO 2 is estimated to be ~300–600 ppm (Milligan et al, 2019), and equilibrium climate sensitivity in the ice‐free early Paleocene is estimated to be 3°C per pCO 2 doubling (Royer, 2016).…”

Near‐Future pCO2 During the Hot Miocene Climatic Optimum

“…SI is less affected than SD by additional environmental and physiological factors besides p CO 2 , such as irradiance levels, moisture, and leaf expansion (Salisbury, 1927). The stomatal proxy methods are by now well‐established in the paleoclimate literature, having been applied to a plethora of plant taxa from a wide variety of geological, ecological, and climatological backgrounds to reconstruct paleo‐ p CO 2 from the Paleozoic until today, generally showing remarkable intermethod consistency (e.g., Barclay & Wing, 2016; Grein et al, 2013; Kürschner et al, 2008; Li et al, 2019; Londoño et al, 2018; Mays et al, 2015; McElwain & Steinthorsdottir, 2017; Milligan et al, 2019; Montañez et al, 2016; Reichgelt et al, 2013; Royer et al, 2001; Steinthorsdottir et al, 2011, 2013; Steinthorsdottir, Porter, et al, 2016; Steinthorsdottir, Vajda, Pole, & Holdgate, 2019; Steinthorsdottir, Vajda, & Pole, 2019; Steinthorsdottir & Vajda, 2015; Tesfamichael et al, 2017; Wagner et al, 1996; Zhou et al, 2020) and are considered one of four most useful proxies for paleo‐ p CO 2 (Beerling & Royer, 2011).…”

An evaluation of Deccan Traps eruption rates using geochronologic data

“…This was a key message sent by the associated "News and Views" piece in the same issue of Science (Burgess, 2019), and the notion that the U−Pb and 40 Ar/ 39 Ar datasets disagreed substantially has been propagated by subsequent discussion and news coverage on Sci-enceMag.org (Kerr and Ward, 2019;Voosen, 2019). Authors of subsequent papers (Henehan et al, 2019;Hull et al, 2020;Linzmeier et al, 2020;Milligan et al, 2019;Montanari and Coccioni, 2019;Sepúlveda et al, 2019) also seem to conclude that the datasets do not agree on the eruption rates of the Deccan Traps and/or that the dataset of Sprain et al (2019) suggests an inflection in eruption rates of Deccan Traps at the KPB.…”