Letter

Nature 461, 1110-1113 (22 October 2009) | doi:10.1038/nature08447; Received 18 May 2009; Accepted 21 August 2009; Published online 13 September 2009

Atmospheric carbon dioxide through the Eocene–Oligocene climate transition

Paul N. Pearson1, Gavin L. Foster2 & Bridget S. Wade3

  1. School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3YE, UK
  2. Bristol Isotope Group, Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
  3. Department of Geology and Geophysics, Texas A&M University, College Station, Texas 77843-3115, USA

Correspondence to: Paul N. Pearson1 Correspondence and requests for materials should be addressed to P.N.P. (Email: pearsonp@cardiff.ac.uk).

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 (Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com) fell below a critical threshold of approx750 p.p.m.v., but the timing and magnitude of Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com 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 Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com before, during and after the climate transition. Our data suggest that a reduction in Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com 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, Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com was between approx450 and approx1,500 p.p.m.v., with a central estimate of approx760 p.p.m.v. The ice cap survived the period of Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com 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 Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com 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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