Global ocean heat content over the past 3 million years

The Pleistocene Epoch is characterized by global cooling and an increase in the intensity and duration of glacial cycles. Regional surface and subsurface ocean temperature records follow distinct trends over this interval, suggesting dynamic changes in zonal and meridional heat transport and ocean circulation. Here we provide a record of global ocean heat content (or mean ocean temperature) over the last 3 million years from ice core noble gas (Xe/Kr) measurements. We find long-term ocean cooling over this interval, a prominent period of cooling coincident with the Plio-Pleistocene transition (~2.7 Ma), and steady temperatures across the mid-Pleistocene transition (1.2-0.8 Ma). Comparisons with a recent global sea surface temperature compilation show broad consistency in long-term cooling, but important differences at the Plio-Pleistocene and mid-Pleistocene transitions. We suggest that the different trends in surface temperature and mean ocean temperature during these intervals are related to a redistribution of heat between the surface and subsurface via changes in deep water formation and upwelling. Our temperature record also permits an estimate of global ice volume changes between 3 and 0.5 Ma through a deconvolution of the benthic foraminiferal δ18O record pointing to a period of enhanced ice sheet growth around the mid-Pleistocene transition.