T280 Geobiology of Critical Transitions: Integrating Fossils, Proxies, and Models II

Wednesday, 4 November 2015
8:00 AM - 12:00 PM
Room 325/326

DYNAMIC SHIFTS IN GLACIAL-INTERGLACIAL ATMOSPHERIC CO2 AND TROPICAL VEGETATION DURING EARTH’S LAST ICEHOUSE

Paper number: T280-10
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Abstract

The Carboniferous—early Permian (325 to 260 Myr) has long been considered a sustained period of low CO2 coupled with rising pO2 to a Phanerozoic maximum (26 to 30%) in the early Permian. Such low CO2 estimates suggest very low radiative forcing given 3% lower solar luminosity at that time, a condition that may have been magnified by pO2-induced higher atmospheric density. The implication of this reduced radiative forcing on the late Paleozoic climate system is strongly debated, in large part due to poorly constrained atmospheric CO2 estimates. We present an integrated pedogenic carbonate and fossil cuticle reconstruction of atmospheric CO2 through 16 million years of the latter half of the Pennsylvanian and earliest Permian developed using a cyclothem series in the Illinois Basin as well as a subset of samples from the Appalachian and Donets basins. Overall, reconstructed CO2 falls below the modeled threshold (560 ppm) for late Paleozoic glacial inception, well within the range of ice sheet stability during the LPIA (up to 840 ppm). The suborbital resolution record reveals CO2 variations between ~200 and 700 ppm with an apparent long eccentricity pacing. Short-term CO2 fluctuations are superimposed on a 106-yr CO2 trend that varies in-step with major sea level changes and glacial advances and retreats inferred from Donets Basin and Midcontinent stratigraphic trends.

Comparison of the CO2 reconstruction and inferred sea level with published paleobotanical records for tropical Pangaea suggests a mechanistic relationship between CO2, glaciation, and major shifts in lowland vegetation, highlighting the important role terrestrial carbon storage likely played in creating the hierarchy of atmospheric CO2 fluctuations. Specifically, substantial changes in floral composition of paleotropical lowlands within eccentricity glacial-interglacial cycles occurred coincident with 200 to 300 ppm fluctuations in CO2. Additionally, three ecologic thresholds in the Pennsylvanian were coincident with major CO2 shifts suggesting a strong role for CO2-forcing of these ecologic events, whether indirectly through its influence on climate or directly through physiological consequences for photosynthesis and plant viability.