The mid-Pliocene (3.3-3.0 million years ago) is an important possible analogue to future, warmer-than-present climates. This interval is the most recent period in Earth's history of sustained global warmth, when atmospheric CO2 concentrations were comparable to the early 21th century, global ice volume was reduced and sea-levels were significantly higher than at present. Relatively few deep ocean temperature records exist from this time interval, but some available data suggest that large differences in temperatures existed between different deep ocean basins. This is in contrast to the modern ocean, which is relatively isothermal across the various basins at similar depth. In order to verify the possibility of a large temperature gradient between the deep Pacific and deep North Atlantic oceans, we generated new benthic foraminiferal carbonate clumped isotope (Δ47) and Mg/Ca bottom water temperatures from Pacific ODP Site 849 and North Atlantic IODP Site U1308. We find that the deep North Atlantic was significantly warmer (by 4°C) and likely more saline than the deep Pacific throughout our study interval, suggesting inefficient heat and salt transport from the Atlantic into the deep Pacific at this time. Our records also cover the enigmatic Marine Isotope Stage (MIS) M2 glacial event at 3.3 Ma, which represents the largest positive oxygen isotope excursion of the Pliocene prior to the intensification of Northern Hemisphere glaation.This event has been cited as a possible failed attempt at establishing Northern Hemisphere glacial-interglacial cycles. The amplitute of cooling observed in our temperature records suggest that much of the observed change in benthic δ18O can be attributed to cooling of the deep ocean rather than a substantial growth of ice on land. This data set contains final calculated bottom water temperatures from Δ47 from both study sites; Mg/Ca, Mn/Ca and Fe/Ca ratios and calculated Mg/Ca bottom water temperatures from both study sites and new stable isotope data from Site U1308.
