The Eocene-Oligocene (E-O) climate transition (ca. 34 Ma) marksa period of Antarctic ice growth and a major step from earlyCenozoic greenhouse conditions toward today's glaciated climatestate. The transition is represented by an increase in deep-seabenthic foraminiferal oxygen isotope (18O) values occurringin two main steps that reflect the temperature and 18O of seawater.Existing benthic Mg/Ca paleotemperature records do not displaya cooling across the transition, possibly reflecting a saturationstate effect on benthic foraminiferal Mg/Ca ratios at deep-watersites. Here we present data from exceptionally well preservedforaminifera deposited well above the calcite compensation depththat provide the first proxy evidence for an 2.5 °C oceancooling associated with the ice growth. This permits interpretationof E-O 18O records without invoking Northern Hemisphere continental-scaleice.