Based on coupled climate model experiments, we suggest an antiphase relationship between the two major coastal upwelling zones in the Atlantic Ocean off northwestern and southwestern Africa. We describe this as an 'upwelling seesaw'. The state of the coastal upwelling seesaw is controlled by variations in the oceanic meridional heat transfer between South and North Atlantic. In particular, we suggest that the Pliocene closure of the Central American Seaway induced a large-scale redistribution of heat in the Atlantic Ocean, leading to an intensification (weakening) of upwelling off southwest (northwest) Africa.