Article abstract
Nature Geoscience 1, 329 - 334 (2008)
Published online: 13 April 2008 | doi:10.1038/ngeo179
Subject Category: Palaeoclimate and palaeoceanography
Stepwise transition from the Eocene greenhouse to the Oligocene icehouse
Miriam E. Katz1,2, Kenneth G. Miller2, James D. Wright2, Bridget S. Wade3,4, James V. Browning2, Benjamin S. Cramer5 & Yair Rosenthal2,3
Abstract
In the largest global cooling event of the Cenozoic Era, between 33.8 and 33.5 Myr ago, warm, high-CO2 conditions gave way to the variable 'icehouse' climates that prevail today. Despite intense study, the history of cooling versus ice-sheet growth and sea-level fall reconstructed from oxygen isotope values in marine sediments at the transition has not been resolved. Here, we analyse oxygen isotopes and Mg/Ca ratios of benthic foraminifera, and integrate the results with the stratigraphic record of sea-level change across the Eocene–Oligocene transition from a continental-shelf site at Saint Stephens Quarry, Alabama. Comparisons with deep-sea (Sites 522 (South Atlantic) and 1218 (Pacific)) 
18O and Mg/Ca records enable us to reconstruct temperature, ice-volume and sea-level changes across the climate transition. Our records show that the transition occurred in at least three distinct steps, with an increasing influence of ice volume on the oxygen isotope record as the transition progressed. By the early Oligocene, ice sheets were 
25%
larger than present. This growth was associated with a relative sea-level decrease of approximately 105 m, which equates to a 67 m eustatic fall.
- Department of Earth and Environmental Science, Rensselaer Polytechnic Inst., Troy, New York 12180, USA
- Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey 08854, USA
- Institute of Marine and Coastal Science, Rutgers University, 71 Dudley Road, New Brunswick, New Jersey 08901, USA
- Department of Geology and Geophysics, Texas A&M University, College Station, Texas 77840, USA
- Department of Geological Sciences, 1272 University of Oregon, Eugene, Oregon 97403-1272, USA
Correspondence to: Miriam E. Katz1,2 e-mail: katzm@rpi.edu
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