Paleoceanography http://dx.doi.org/10.1029/2010PA002055 (2011)
Variations in atmospheric CO2 levels between 4.6 and 2 million years ago correspond closely to the extent of glaciation on Greenland, suggests an analysis of marine sediments.
Gretta Bartoli of ETH Zürich and colleagues used the boron isotope composition of foraminiferal shells from the Caribbean Sea to reconstruct atmospheric CO2 concentrations during the period spanning the transition from the warm climate of the Pliocene epoch to the glacial–interglacial cycles of the Pleistocene epoch. They found a broad trend of decreasing CO2 levels, interspersed with more short-lived oscillations. The periods of lower atmospheric CO2 coincided with the appearance of transient ice sheets on Greenland, most notably between 3.43 and 3.32 million years ago. Intriguingly, their CO2 estimates are in line with inferred thresholds for Greenland glaciation.
The transition to permanently low, pre-industrial atmospheric CO2 levels occurred 2.7 million years ago, and may have been linked to the stratification of polar oceans and enhanced marine productivity.
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Newton, A. Pliocene glaciation. Nature Geosci 4, 734 (2011). https://doi.org/10.1038/ngeo1315
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DOI: https://doi.org/10.1038/ngeo1315
