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Science 27 February 2009:
Vol. 323. no. 5918, pp. 1187 - 1190
DOI: 10.1126/science.1166368
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Reports

Global Cooling During the Eocene-Oligocene Climate Transition

Zhonghui Liu,1,2* Mark Pagani,1* David Zinniker,1 Robert DeConto,3 Matthew Huber,4 Henk Brinkhuis,5 Sunita R. Shah,6 R. Mark Leckie,3 Ann Pearson6

About 34 million years ago, Earth's climate shifted from a relatively ice-free world to one with glacial conditions on Antarctica characterized by substantial ice sheets. How Earth's temperature changed during this climate transition remains poorly understood, and evidence for Northern Hemisphere polar ice is controversial. Here, we report proxy records of sea surface temperatures from multiple ocean localities and show that the high-latitude temperature decrease was substantial and heterogeneous. High-latitude (45 degrees to 70 degrees in both hemispheres) temperatures before the climate transition were ~20°C and cooled an average of ~5°C. Our results, combined with ocean and ice-sheet model simulations and benthic oxygen isotope records, indicate that Northern Hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time.

1 Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA.
2 Department of Earth Sciences, University of Hong Kong, Hong Kong, People's Republic of China.
3 Department of Geosciences, University of Massachusetts-Amherst, Amherst, MA 01003, USA.
4 Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907, USA.
5 Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands.
6 Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.

* To whom correspondence should be addressed. E-mail: zhliu{at}hku.hk (Z.L.); mark.pagani{at}yale.edu (M.P.)

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Science. ISSN 0036-8075 (print), 1095-9203 (online)