Antarctic Ice Sheet variability across the Eocene-Oligocene boundary climate transition

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Science  10 Mar 2016:
DOI: 10.1126/science.aab0669

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About 34 million years ago (Ma) Earth’s climate cooled and an ice sheet formed on Antarctica as atmospheric CO2 fell below ~750 ppm. Sedimentary cycles from a drill core in western Ross Sea provide the first direct evidence of orbitally-controlled glacial cycles between 34–31 Ma. Initially, under atmospheric CO2 levels ≥ 600 ppm, a smaller Antarctic Ice Sheet, (AIS) restricted to the terrestrial continent, was highly responsive to local insolation forcing. A more stable, continental-scale ice sheet calving at the coastline, did not form until ~32.8 Ma coincident with the first time atmospheric CO2 levels fell below ~600 ppm. Our results provide new insights into the potential of the AIS for threshold behavior, and its sensitivity to atmospheric CO2 concentrations above present day levels.

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