The focus of this ABR project, through collaboration with colleagues and students, is several key issues regarding the late Paleozoic Ice Age that remain poorly constrained ? i.e., the true magnitude of CO2 shifts, late Paleozoic climate sensitivity, and the nature of the linkages to regional hydroclimate, soil productivity, ice sheet stability, and major restructuring of paleotropical vegetation. The proposed two-component research plan focuses on a ~9 Myr interval of the end-Carboniferous, in particular a hypothesized ?climate event? during the mid-to-late Pennsylvanian transition. Component 1 will evaluate how paleo-pCO2 varied through this interval, and its role in widespread aridity and major vegetation restructuring. Anticipated products include a cyclothem-scale (~105 yr) stomatal index-based record of paleo-pCO2 using two long-ranging and well understood, wetland seed-fern taxa from the Illinois Basin. Integration of xerphytic walchian conifer cuticles from select cyclothems will permit comparison of SI-based CO2 estimates for wet- and dry-land flora and interglacial-glacial-scale CO2 variability. Compound-specific isotopic analysis (äD and ä13C) of the same fossil cuticles will further constrain the rate of onset and magnitude of paleoaridity in the Illinois Basin and test for causality between pCO2, terrestrial paleotropical aridity, and floral ecological restructuring. A proposed 4-year long-duration, plant growth experiment under controlled atmospheric O2:CO2 ratios and inferred Carboniferous climate conditions will provide novel insight into the fossil-based trends. Integration of results with paleobotanical data and our paleoclimate proxy records will be used to develop an appropriate vegetation-feedback component for our climate modeling efforts. The 2nd research component will develop a cyclothem-scale ä18O apatite record using already collected conodonts (CAI 1-3) from two paleotropical basins for the same end-Carboniferous interval. The objective is to test the hypothesis that periods of CO2-forced global warming also drove ice sheet ablation and a reduction in the amplitude of high-frequency (104-105 yr) glacioeustasy. Through collaboration, we will test the potential of the ?carbonate clumped isotope? method to define sea-surface temperatures of precipitation from a suite of exceptionally well-preserved and diagenetically screened brachiopods from the same geological sections. We anticipate that for the best-preserved brachiopods, this approach should permit reconstruction of Pennsylvanian SSTs and ä18Oseawater, and ultimately the most rigorous evaluation of relative changes in ice volume during the LPIA to date.
