A synthesis of Late Oligocene through Miocene deep sea temperatures as inferred from foraminiferal Mg/Ca ratios

Published benthic foraminiferal Mg/Ca records have been compiled that span the latest Oligocene through Miocene, including new data for the South Atlantic. This synthesis, the first such of Mg/Ca data, necessitates consideration of uncertainties and limitations and provides a general perspective on the evolution of deep-sea temperatures over this period. Published Mg/Ca records show temperature patterns through the Miocene that are consistent with those first synthesized by Kennett (1985) utilizing isotope and other data. Accordingly, the early Miocene was an interval of relative warmth culminatinginaclimaticoptimumat � 16Mathatwascharacterizedbythewarmest(Mg-derived) temperatures of the past 20 million years. After the climatic optimum, palaeotemperatures dropped by 3‐4 � C during the second major advance of Antarctic ice between � 15Ma and 13Ma. For the late Miocene, between 11 and 8.5Ma, a distinct increase in benthic foraminiferal Mg/Ca ratios at two Atlantic sites provides evidence for deep to intermediate water circulation changes. Thereafter, temperatures close to modern are recorded at all sites. Assuming constant seawater Mg/Ca ratios through time, it can be concluded that the early Miocene climate was generally warmer than today and that by the late Miocene temperatures approached modern values.