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Science 11 January 2008:
Vol. 319. no. 5860, pp. 189 - 192
DOI: 10.1126/science.1148777
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Reports

Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse

André Bornemann,1,2* Richard D. Norris,1 Oliver Friedrich,1,3 Britta Beckmann,4 Stefan Schouten,5 Jaap S. Sinninghe Damsté,5 Jennifer Vogel,1 Peter Hofmann,4 Thomas Wagner6

The Turonian (93.5 to 89.3 million years ago) was one of the warmest periods of the Phanerozoic eon, with tropical sea surface temperatures over 35°C. High-amplitude sea-level changes and positive {delta}18O excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth. New {delta}18O data from the tropical Atlantic show synchronous shifts ~91.2 million years ago for both the surface and deep ocean that are consistent with an approximately 200,000-year period of glaciation, with ice sheets of about half the size of the modern Antarctic ice cap. Even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets, calling into question the common assumption that the poles were always ice-free during past periods of intense global warming.

1 Scripps Institution of Oceanography, University of California, San Diego, Geosciences Research Division, 9500 Gilman Drive, La Jolla, CA 92093–0244, USA.
2 Institut für Geophysik und Geologie, Universität Leipzig, Talstraße 35, D-04103 Leipzig, Germany.
3 School of Ocean and Earth Science, National Oceanography Centre, European Way, Southampton SO14 3ZH, UK.
4 Institut für Geologie und Mineralogie, Universität Köln, Zülpicher Straße 49a, D-50674 Köln, Germany.
5 Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research, Post Office Box 59, 1790 AB Den Burg, Texel, Netherlands.
6 School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.

* To whom correspondence should be addressed. E-mail: a.bornemann{at}uni-leipzig.de

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