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Atmospheric carbon dioxide through the Eocene–Oligocene climate transition


Geological and geochemical evidence1,2,3 indicates that the Antarctic ice sheet formed during the Eocene–Oligocene transition4, 33.5–34.0 million years ago. Modelling studies5,6 suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels () fell below a critical threshold of 750 p.p.m.v., but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear. Here we use the boron isotope pH proxy7,8 on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania9,10 to estimate before, during and after the climate transition. Our data suggest that a reduction in occurred before the main phase of ice growth, followed by a sharp recovery to pre-transition values and then a more gradual decline. During maximum ice-sheet growth, was between 450 and 1,500 p.p.m.v., with a central estimate of 760 p.p.m.v. The ice cap survived the period of recovery, although possibly with some reduction in its volume, implying (as models predict11) a nonlinear response to climate forcing during melting. Overall, our results confirm the central role of declining in the development of the Antarctic ice sheet (in broad agreement with carbon cycle modelling12) and help to constrain mechanisms and feedbacks associated with the Earth’s biggest climate switch of the past 65 Myr.

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Figure 1: Deep-sea oxygen isotope records across the EOT compared with boron isotopes from Tanzania.
Figure 2: Sensitivity of pH and atmospheric carbon dioxide estimates to δ11B for sea water, with modelled atmospheric p CO 2 thresholds for ice growth.
Figure 3: Reconstructed compared with the deep-sea benthic foraminiferal stable isotope record.


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This work was supported by NERC grants to P.N.P., B.S.W. and G.L.F. We thank the Tanzania Petroleum Development Corporation, the Tanzania Commission for Science and Technology and the Tanzania Drilling Project field team for support. We are grateful to T. Elliott for discussions.

Author Contributions P.N.P. led the study and fieldwork, prepared foraminifer samples for isotope analysis and wrote the initial draft. G.L.F. conducted all isotope and trace element analyses and calculations and drafted the figures. B.S.W. contributed to fieldwork and prepared foraminifer samples for trace element analyses. All authors contributed to the final text.

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Correspondence to Paul N. Pearson.

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Supplementary Data

This file consists of Supplementary Table 1 which contains Boron Isotopic Data T. ampliapertura (212-250 mm) from TDP12 and TDP17 across the Eocene-Oligocene Transition and Supplementary Table 2 which contains Mg/Ca Data for samples from TDP12 and TDP17. (XLS 35 kb)

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Pearson, P., Foster, G. & Wade, B. Atmospheric carbon dioxide through the Eocene–Oligocene climate transition. Nature 461, 1110–1113 (2009).

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