Dynamical changes in the tropical Pacific warm pool and zonal SST gradient during the Pleistocene

In the late Pleistocene, the atmospheric carbon dioxide concentration (pCO(2)) is thought to be a primary driving force for tropical sea surface temperature (SST) change because glacial-interglacial changes in tropical Pacific SST covary with pCO(2). However, if the regional radiative effects of pCO(2) were the only agent of change, tropical SST gradients should have remained similar as pCO(2) varied with time. Instead, a new record of SST from the west Pacific shows that tropical SST gradients were different, even reversed, in the past, suggesting an important role for dynamical circulation changes. Specifically, changes in the temperature of upwelled source water, in addition to local pCO(2) forcing, influenced tropical Pacific SST. These dynamical changes, rather than pCO(2), may have shifted the background state of the tropics and even helped set the stage for the mid-Pleistocene transition.