Cenozoic Deep-Sea Temperatures and Global Ice Volumes from Mg/Ca in Benthic

A deep-sea temperature record for the past 50 million years has been produced from the magnesium/calcium ratio (Mg/Ca) in benthic foraminiferal calcite. The record is strikingly similar in form to the corresponding benthic oxygen isotope (d18O) record and deÞnes an overall cooling of about 12¡C in the deep oceans with four main cooling periods. Used in conjunction with the benthic d18O record, the magnesium temperature record indicates that the Þrst major ac-cumulation of Antarctic ice occurred rapidly in the earliest Oligocene (34 million years ago) and was not accompanied by a decrease in deep-sea temperatures. Earth’s climate is widely understood to have undergone dramatic changes over the past 100 million years (My) from the so-called mid-Cretaceous “greenhouse ” to the late Cenozoic “icehouse ” (1, 2). The long-term cooling over this period is thought to have resulted from a combination of factors that altered the amoun