PERMO-CARBONIFEROUS ATMOSPHERIC PCO2, CLIMATE AND GONDWANAN GLACIATION HISTORY

An integration of estimated paleo-atmospheric pCO₂, tropical marine and continental paleotemperatures, and glaciation history from southern Gondwana over a 40 m.y. period of Permo-Carboniferous time reveals a more dynamic transition from the Gondwanan Ice Age to a greenhouse world than previously recognized. An estimation of tropical sea-surface temperatures from a global compilation of δ¹⁸O values of calcitic brachiopods indicates the onset of rising temperatures in the early Sakmarian interrupted by significantly cooler intervals in the early Artinskian, Kungarian and Wordian. Quantitative estimates of paleo-atmospheric pCO₂ were developed over this interval using the δ¹³C values of pedogenic carbonates and goethites and fossil plant material from the Eastern Shelf of the Midland Basin, and Paradox and Orogrande Basins and constrained by Monte Carlo simulations. Best estimates of Late Paleozoic pCO₂ delineate a rise from present-day levels in the early Early Permian (2nd half of the Sakmarian) to values of up to 2500 to 3500 ppmv by end-Artinskian time. Atmospheric CO₂ concentrations declined once again before the close of the Early Permian (Kungarian). Superimposed on this longer-term trend are shorter-term fluctuations in pCO₂ during the early Artinskian and (possibly) end-Carboniferous. Parallel shifts in paleo-atmospheric CO₂ and earth surface temperatures indicate a well-coupled, Late Paleozoic climate-pCO₂ system. Distribution of glacigenic deposits in Antarctica and Australia indicate multiple discrete and short-lived (1 to 4 my) episodes of glaciation and colder modes that appear to coincide with short-lived but large magnitude drops in atmospheric pCO₂, tropical marine temperatures and relative sea-level. Warmer periods separating glaciations appear to have been synchronous with rises in pCO₂, surface temperatures, and relative sea-level. This apparent CO₂-climate-glaciation link suggests that atmospheric CO₂ levels may have been the primary driver for the repeated buildup and retreat of continental ice sheets during the Late Paleozoic.