Quaternary deep sea temperature histories derived from benthic foraminiferal Mg/Ca

We have generated benthic foraminiferal Mg/Ca records from eastern tropical Atlantic core M16772 (3.9 km) and eastern tropical Pacific core TR163-31P (3.2 km) to assess the potential for using benthic Mg-paleothermometry to reconstruct Quaternary bottom water temperature histories. Variations in Mg/Ca records from both the Atlantic and Pacific show a significant correlation with climatic oscillations of the last 330 kyr. Shell Mg/Ca peaks during interglacial episodes, with marine isotope stage (MIS) 5e Mg/Ca nearly matching Holocene values in both cores. Lower Mg/Ca values occur during glacial intervals. To estimate temperatures from downcore Mg/Ca, we have augmented the published Cibicidoides sp. Mg/Ca–temperature dataset [Rosenthal et al., Geochim. Cosmochim. Acta 61 (1997) 3633–3643] with new data to include the temperature range of deep waters. Applying the 10.9% change in Mg/Ca per °C defined by the expanded calibration to the deep Atlantic data implies glacial–interglacial shifts in deep water temperature of 2–4°C over the last 300 kyr. Temperature estimates are comparable to deep Atlantic temperature changes proposed by Labeyrie et al. [Nature 327 (1987) 477–482]. There is greater uncertainty in deriving temperatures from the tropical Pacific core due to a limited Uvigerina spp. core top calibration set; however, glacial–interglacial temperature oscillations appear to be on the order of 2–3°C. In addition, core TR163-31P records clear millennial-scale Mg/Ca and δ18O oscillations in MIS 3 corresponding to temperature fluctuations of >0.5°C. Additional calibration studies are needed to address potential secondary effects on Mg/Ca.