Current Research in EEPS Seminar: Dr. Isabel Montañez – University of California, Davis
Reconstructing the Earth System in Deep Time
Earth system science, the study of our planet as an integrated set of subsystems that drive planetary function, is a modern holistic approach to understanding rapidly evolving issues such as climate change, ecosystem stress, and environmental degradation. An Earth system approach is transferable to the geologic past, i.e., the deep time, made possible by the advent of high precision radioisotope dating, the potential for astronomically calibrating stratigraphic intervals, and the application of Earth System (climate) Models and process-based ecosystem models to deep time studies. In this talk I present our efforts over the past 15 years to develop a ‘whole-Earth’ reconstruction during the Late Paleozoic Ice Age (LPIA), ~300 Ma. The ubiquitous presence of cyclothems, the fundamental stratigraphic unit for this time, throughout paleotropical successions coupled with single-zircon U-Pb CA-TIMS ages documents eccentricity scale cyclicity and the potential for orbital tuning of stratigraphic and geochemical proxy records. We use this paleotropical chronostratigraphic framework to reconstruct onlap-offlap history, to build and correlate terrestrial and marine proxy records, and to better understand spatial and temporal variability in paleo-surface seawater composition and climate conditions through the LPIA. A multi-proxy record of atmospheric CO2 over 40 million years reveals CO2 variability between ~160 and 750 ppm with fluctuations in-step with major sea level changes inferred from cyclothems and glacial advances and retreats constrained by high-latitude geologic records. Comparison of the CO2 reconstruction with paleobotanical records for tropical Euramerica indicates coincidence between CO2 change and repeated restructuring of Pangaean tropical forests on the eccentricty to million-year scales. Integration of plant fossil data with process-based ecosystem modelling permits us to constrain the paleo-physiology/functioning of these extinct plants and to suggest possible ecosystem-scale vegetation-climate-CO2 feedbacks that would have influenced water and carbon cycling. For the higher latitudes, integration of high-precision U-Pb ages with detrital zircon U-Pb geochronology for successions in west-central Gondwana (Argentina, Brazil, and southern Africa) provides an evolving view of the glaciation history of southern Gondwana and its mechanistic link to climate in the lower latitudes.