An atmospheric p CO ₂ reconstruction across the Cretaceous-Tertiary boundary from leaf megafossils

Abstract

The end-Cretaceous mass extinctions, 65 million years ago, profoundly influenced the course of biotic evolution. These extinctions coincided with a major extraterrestrial impact event and massive volcanism in India. Determining the relative importance of each event as a driver of environmental and biotic change across the Cretaceous-Tertiary boundary (KTB) crucially depends on constraining the mass of CO2 injected into the atmospheric carbon reservoir. Using the inverse relationship between atmospheric CO2 and the stomatal index of land plant leaves, we reconstruct Late Cretaceous-Early Tertiary atmospheric CO2 concentration (pCO2) levels with special emphasis on providing a pCO2 estimate directly above the KTB. Our record shows stable Late Cretaceous͞Early Tertiary background pCO2 levels of 350 -500 ppm by volume, but with a marked increase to at least 2,300 ppm by volume within 10,000 years of the KTB. Numerical simulations with a global biogeochemical carbon cycle model indicate that CO2 outgassing during the eruption of the Deccan Trap basalts fails to fully account for the inferred pCO2 increase. Instead, we calculate that the postboundary pCO2 rise is most consistent with the instantaneous transfer of Ϸ4,600 Gt C from the lithic to the atmospheric reservoir by a large extraterrestrial bolide impact. A resultant climatic forcing of ؉12 W⅐m ؊2 would have been sufficient to warm the Earth's surface by Ϸ7.5°C, in the absence of counter forcing by sulfate aerosols. This finding reinforces previous evidence for major climatic warming after the KTB impact and implies that severe and abrupt global warming during the earliest Paleocene was an important factor in biotic extinction at the KTB.

Correlated terrestrial and marine evidence for global climate changes before mass extinction at the Cretaceous–Paleogene boundary

“…Second, the fossil fern has not been found in other stratigraphic horizons so as to allow calibration of its stomatal indices to baseline values. Therefore, the fossil stomatal data (20) appear to us to be reliable indicators neither of high nor low pCO 2 during the earliest Paleocene.…”

“…Paleobotanical reports have suggested long-term cooling across the K-P in Asia (16), no temperature change (10) or a major temperature increase soon after the boundary (17) in the Raton Basin of New Mexico and Colorado, and latest Cretaceous warming followed by a cooler Paleocene in North Dakota (18). Fine-scale correlations between continental and marine temperature records near the K-P have previously not been attempted (5,19), though such data would help to assess the global extent of warming and cooling events as well as the correlation of partial pressure of CO 2 (pCO 2 ) and temperature (20,21). Detection of climatic shifts just before the K-P would refine understanding of the mass extinction event by making it possible to distinguish the effects of climate change from those of bolide impact on biodiversity.…”

Severity of ocean acidification following the end-Cretaceous asteroid impact

“…Beerling et al (16) used data (the stomatal index of land plant leaves) and a box model; they suggested that atmospheric pCO 2 increased from 350 to 500 to 2,300 ppmv across the K/Pg boundary [although such a rise is not seen in other proxy data (17)], from which they inferred an instantaneous transfer of ca. 4,600 Pg C from rocks to the atmosphere.…”

Angiosperms Helped Put the Rain in the Rainforests: The Impact of Plant Physiological Evolution on Tropical Biodiversity1

“…With the transition to a hothouse climatic regime during the Permian, seasonally dry conditions spread throughout the tropics to produce more savannah-like vegetation, and everwet conditions were limited to islands and narrow coastal areas of continents provided with significant maritime precipitation (Ziegler et al, 2003). Predominance of rainfall seasonality and tropical aridity persisted through most of the Mesozoic until the expansion of high precipitation conditions beginning in the early Late Cretaceous and reaching a maximum extent in the Eocene (Parrish et al, 1982;Parrish, 1987;Upchurch & Wolfe, 1987;Vakhrameev, 1991;Morley, 2000;Beerling & Woodward, 2001;Ziegler et al, 2003;Ufnar et al, 2008).…”