CO2 drawdown following the middle Miocene expansion of the Antarctic Ice Sheet

The development of a permanent, stable ice sheet in East Antarctica happened during the middle Miocene, about 14 million years (Myr) ago. The middle Miocene therefore represents one of the distinct phases of rapid change in the transition from the "greenhouse" of the early Eocene to the "icehouse" of the present day. Carbonate carbon isotope records of the period immediately following the main stage of ice sheet development reveal a major perturbation in the carbon system, represented by the positive delta C-13 excursion known as carbon maximum 6 ("CM6"), which has traditionally been interpreted as reflecting increased burial of organic matter and atmospheric pCO(2) drawdown. More recently, it has been suggested that the delta C-13 excursion records a negative feedback resulting from the reduction of silicate weathering and an increase in atmospheric pCO(2). Here we present high-resolution multi-proxy (alkenone carbon and foraminiferal boron isotope) records of atmospheric carbon dioxide and sea surface temperature across CM6. Similar to previously published records spanning this interval, our records document a world of generally low (similar to 300 ppm) atmospheric pCO(2) at a time generally accepted to be much warmer than today. Crucially, they also reveal a pCO(2) decrease with associated cooling, which demonstrates that the carbon burial hypothesis for CM6 is feasible and could have acted as a positive feedback on global cooling. Citation: Badger, M. P. S., C. H. Lear, R. D. Pancost, G. L. Foster, T. R. Bailey, M. J. Leng, and H. A. Abels (2013), CO2 drawdown following the middle Miocene expansion of the Antarctic Ice Sheet, Paleoceanography, 28, 42-53, doi:10.1002/palo.20015.