Orbital and CO₂ forcing of late Paleozoic continental ice sheets

Contrasting views of the size, duration, and history of the Gondwanan continental ice sheets have been proposed from late Palcozoic glaciological and sedimentological evidence. To evaluate these differing views, a coupled ice sheet-climate model is used to simulate continental ice sheets under a wide range of late Paleozoic orbital and pCO₂ conditions. The model experiments indicate that orbital variations at PCO₂ concentrations below 2X pre-industrial atmospheric levels (PAL; 280 ppm) produce large changes in late Paleozoic ice volume (∼ 1.3 x 10⁸ km³) and sea level (∼20 to 245 m). Between 2 and 8X PAL Gondwana continental ice is simulated only under the most extreme Southern Hemisphere cold summer orbit, but still produces significant ice volumes (∼8-12 x 10⁷ km³). Our results highlight the important role of atmospheric CO₂ in determining the distribution, volume, and stability of late Paleozoic ice sheets, factors that ultimately impacted sea level, cyclothem deposition, and global climate, and reconcile disparate views of the Late Paleozoic Ice Age.