EVIDENCE FOR A ROBUST CO2- CLIMATE LINK DURING THE LATE PALEOZOIC GONDWANAN ICE AGE

Integration of paleo-atmospheric pCO₂ and paleo-temperature reconstructions derived from the stable isotope compositions of pedogenic minerals, contemporaneous permineralized fossil plant matter, and marine carbonates, with paleoprecipitation and paleoweathering trends inferred from paleosol morphologies indicates a relatively robust CO₂-Climate link during the latest Carboniferous through early Middle Permian that may provide insight into the nature of the final stages of the late Paleozoic Gondwanan Ice Age.

Paleo-atmospheric pCO₂  and paleoclimate proxy records were developed for a ~30 million year interval of the latest Carboniferous (late Stephanian) through Early Permian (Kungarian) using fossil soils developed within Permo-Carboniferous alluvial deposits of the Midland and Paradox basins, southwestern U.S., and published late Paleozoic tropical marine carbonate d¹⁸O compositions. Atmospheric pCO₂ estimates suggest that minimum values similar to present-day CO₂ levels were reached during the latest Asselian and earliest Sakmarian after dropping from moderate levels (>500 to 1200 ppmv) in the latest Carboniferous.  Moderate latest Carboniferous CO₂ levels were coincident with elevated mean annual surface temperatures and intensified precipitation during the latest Carboniferous to earliest Permian (Asselian).  A stepped, long-term rise in paleo-atmospheric pCO₂ levels from the earliest Permian minimum to maximum levels of 1500 ppmV and possibly up to 2500 ppmV by latest Early Permian-early Middle Permian time was temporarily arrested in the earliest Artinskian by a superimposed short-term fall in CO₂ levels to values of 500 ppmV ±300 ppmV.  This short-term fluctuation in pCO₂ lasted 1 to 2 m.y. and coincides with a short-lived shift to decreased mean annual temperatures recorded in both marine and terrestrial proxies and with evidence for increased net soil moisture budgets. Comparison of paleoatmospheric pCO₂ and paleo-temperature records with independent evidence for the nature and timing of Gondawanan glaciation supports recently developed models for discrete and relatively short-lived (m.y. time-scale) glacial intervals rather than protracted glaciation during this portion of the late Paleozoic.