RESOLVING VEGETATION-CO2-CLIMATE FEEDBACKS DURING THE LAST ICEHOUSE — AN ELT COLLABORATIVE APPROACH

Decades of study of the late Paleozoic icehouse (LPIA) reveal its dynamic glacial, sea-level, and climate history including growing evidence that glacial-interglacial transitions, at a hierarchy of time-scales (10⁵ yr to millions of years), may have been coupled to changes in atmospheric pCO₂. Here we use a multi-proxy approach (pedogenic carbonate paleobarometry, fossil leaf stomatal index, and a plant physiology-based model) to reconstruct paleo-CO₂ variability over the late Carboniferous. Paleo-CO₂ estimates (~300 to 900 ppmv) are comparable to the anticipated shift in CO₂ from preindustrial to projected levels under a spectrum of energy-economic models — levels that greatly exceeded those of the Cenozoic icehouse. Integration of paleo-CO₂ with sedimentologic, paleosol and fossil plant proxy records have the potential to provide unique insight into how physical, chemical and terrestrial ecosystem processes and associated feedbacks in the Earth system functioned during an icehouse under evolving atmospheric CO₂ concentrations.

Our late Paleozoic climate models suggest that vegetation-CO₂-climate feedbacks had the potential to push the climate system between glacial and interglacial states and to strongly modify the climate regime within these states. Documented shifts in the composition of paleotropical flora between inferred glacial and interglacial states within eccentricity-paced cycles and on million-year time-scales further support a key role of vegetation-CO­₂-climate feedbacks in climate transitions. This Earth-Life Transitions collaborative research integrates empirical, plant growth chamber experimental, and modeling approaches over a spectrum of time- (10¹ to 10⁶ yr) and spatial-scales (leaf-to-canopy-to-global climate system) to critically evaluate the roles of CO₂- and orbital-forcing and vegetation-climate feedbacks in promoting glacial-interglacial transitions during the LPIA. The nature of this hypothesis-driven research and preliminary results will be overviewed in this presentation.