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Geology; March 2008; v. 36; no. 3; p. 251-254; DOI: 10.1130/G24584A.1
© 2008 Geological Society of America
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Cooling and ice growth across the Eocene-Oligocene transition

Caroline H. Lear1, Trevor R. Bailey2, Paul N. Pearson3, Helen K. Coxall3 and Yair Rosenthal4

1 School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3YE, UK
2 Geology Department, Amgueddfa Cymru–National Museum Wales, Cathays Park, Cardiff CF10 3NP, UK
3 School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3YE, UK
4 Institute of Marine and Coastal Sciences and Department of Geology, Rutgers, The State University of New Jersey, 71 Dudley Road, New Brunswick, New Jersey 08901, USA

The Eocene-Oligocene (E-O) climate transition (ca. 34 Ma) marks a period of Antarctic ice growth and a major step from early Cenozoic greenhouse conditions toward today's glaciated climate state. The transition is represented by an increase in deep-sea benthic foraminiferal oxygen isotope ({delta}18O) values occurring in two main steps that reflect the temperature and {delta}18O of seawater. Existing benthic Mg/Ca paleotemperature records do not display a cooling across the transition, possibly reflecting a saturation state effect on benthic foraminiferal Mg/Ca ratios at deep-water sites. Here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an ~2.5 °C ocean cooling associated with the ice growth. This permits interpretation of E-O {delta}18O records without invoking Northern Hemisphere continental-scale ice.

Key Words: Eocene • Oligocene • climate • ice sheets • temperature • Cenozoic






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