Resolving a Climatic Conundrum: Linking pCO2 Estimates to Oceanographic and Antarctic Climate Records for the Early Icehouse World (34-16 Ma)

An apparent decoupling between recently published oxygen isotopic data and other paleoclimate proxies for the span from 26-16 Ma is resolved by calibration against global sea-level estimates obtained from backstripping continental margin stratigraphy. Calibrated isotopic data compare favorably with stratigraphic and biological data from Antarctica, and with estimates of atmospheric pCO2 throughout the Oligocene to early Miocene (34-16 Ma). They also provide new estimates of ice volume, suggesting that the East Antarctic Ice Sheet grew to as much as 30% greater than the present-day ice volume at glacial maxima during that span. This conclusion is corroborated by seismic and stratigraphic data from the Antarctic margin that suggest that the ice sheet may have covered much of the continental shelf during Oligocene and early Miocene glacial maxima. Palynological data suggest long-term cooling during the Oligocene, with cold near tundra-like environments developing along the coast during glacial minima no later than the late Oligocene. A possible mechanism for this long-term cooling is a decrease in atmospheric pCO2 from the middle Eocene to Oligocene, reaching near pre-industrial levels by the latest Oligocene and remaining at those depressed levels throughout the Miocene.