The applicability of paired Mg/Ca and (sub 18) O/ (sub 16) O measurements is explored on benthic foraminifera from Southern Ocean site 747 to paleoceanographic reconstructions on pre-Pleistocene timescales. The focus is on the late Oligocene through Pleistocene (27-0 Ma) history of paleotemperatures and the evolution of the (sub 18) O values of seawater. Absolute paleotemperature estimates depend on assumptions of how Mg/Ca ratios of seawater have changed over the past 27 Myr, but relative changes that occur on geologically brief timescales are robust. Results indicate that at the Oligocene to Miocene boundary (23.8 Ma), temperatures lag the increase in global ice-volume deduced from benthic foraminiferal 18O values, but the smaller-scale Miocene glaciations are accompanied by ocean cooling of 1 degrees C. During the mid-Miocene phase of Antarctic ice sheet growth water temperatures cool by 3 degrees C. Unlike the benthic foraminiferal (sub 18) O values. The onset of significant Northern Hemisphere glaciation during the late Pliocene is synchronous with an 4 degrees C cooling at site 747. The Mg/Ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes, which can lead to misinterpretations of the (sub 18) O record. (modified journ. abst.)