Coupling of CO_2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years

• Published in: Science
• Main Authors: Tripati, Aradhna K., Roberts, Christopher D., Eagle, Robert A.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Association for the Advancement of Science 2009
• Subjects: Ner; Ice Sheet
• Online Access: https://doi.org/10.1126/science.1178296

The carbon dioxide (CO_2) content of the atmosphere has varied cyclically between ~180 and ~280 parts per million by volume over the past 800,000 years, closely coupled with temperature and sea level. For earlier periods in Earth's history, the partial pressure of CO_2 (pCO_2) is much less certain, and the relation between pCO_2 and climate remains poorly constrained. We use boron/calcium ratios in foraminifera to estimate pCO_2 during major climate transitions of the past 20 million years. During the Middle Miocene, when temperatures were ~3° to 6°C warmer and sea level was 25 to 40 meters higher than at present, pCO_2 appears to have been similar to modern levels. Decreases in pCO_2 were apparently synchronous with major episodes of glacial expansion during the Middle Miocene (~14 to 10 million years ago) and Late Pliocene (~3.3 to 2.4 million years ago). © 2009 American Association for the Advancement of Science. 26 June 2009; accepted 28 September 2009; published online 8 October 2009. We thank K. Caldeira, H. Elderfield, J. Eiler, T. Naish, D. Sigman, anonymous reviewers, and the editor for their comments on this work, which substantially improved the manuscript. We also thank J. Booth, E. Khadun, O. Shorttle, L. Thanalasundaram, and A. Bufe for invaluable assistance with sample preparation; L. Booth, J. Day, and M. Greaves (supported by grant NE/F004966/1) for technical assistance; L. Lisiecki for assistance with the age model; and S. Crowhurst, A. Gagnon, S. John, N. Meckler, B. Passey, N. Thiagarajan, and J. Yu for discussing this work. Support was provided to A.K.T. by UCLA, National Environmental Research Council (NERC) (fellowship NE/D009049/1), and Magdalene College; to C.D.R. by NERC (studentship NER/S/A/2006/14070); and to R.A.E. by a Caltech Chancellors Postdoctoral Scholarship. Samples for this study were obtained from the Godwin Laboratory sample archives and the Ocean Drilling Program.