Sea surface temperature reconstruction for the Pliocene-Pleistocene climate transition

When comparing new sea surface temperature (SST) records between the western and eastern equatorial Pacific spanning the last 3.2 Ma, we found that the zonal temperature gradient over the entire tropical Pacific irreversibly increased by 3 to 4 °C from 2.2 to 2.0 Ma. Here, we suggest a pronounced increase in atmospheric circulation from a weak to a strong zonal Walker circulation (WC) during the early Pleistocene. Evidence from other oceanic areas also suggests a strengthening in the meridional Hadley circulation (HC) during the same time period. Therefore, we also suggest that the invigoration of both atmospheric circulation patterns was intimately coupled during the Plio-Pleistocene transition, and likely linked to a shrinkage in the zonal extension of the tropical to subtropical warm-sphere associated with a prominent increase in the pole to equator temperature gradient. Our conclusion refutes assumptions that the intensification of atmospheric circulation in the tropics and subtropics significantly contributed to the initiation of continental ice sheet formation at high latitudes, since the onset of extensive Northern Hemisphere Glaciation (NHG) occurred ~2.75 Ma ago, in the late Pliocene. Instead, the development of a stronger atmospheric circulation ~2.2-2.0 Ma ago could have significantly contributed to the Plio-Pleistocene climate cooling.