Mediterranean heat injection to the North Atlantic delayed the intensification of Northern Hemisphere glaciations

The intensification of the Northern Hemisphere glaciations at the end of the Pliocene epoch represents one of the most substantial climatic shifts during Cenozoic. Paradoxically, sea surface temperatures in the high latitude North Atlantic Ocean increased between 2.9–2.7 Ma, against a background of global cooling and declining atmospheric pCO₂. To investigate the origin of this high latitude warming, we obtained sedimentary geochemical proxy data from the Gulf of Cadiz to reconstruct the variability of Mediterranean Outflow Water, an important heat source to the North Atlantic. In fact, we find evidence for enhanced production of Mediterranean Outflow Water during the mid-Pliocene to late Pliocene. We argue that the injection of this warm water on intermediate levels drove a sub-surface heat channel into the high-latitude North Atlantic where it warmed the sea surface. We further used Earth System Models to numerically constrain the impact of enhanced Mediterranean Outflow Water production on the northward heat transport within the North Atlantic. In accord with the proxy evidence, the numerical model results show the formation of a sub-surface channel that funneled heat from the subtropics into the high latitude North Atlantic. We further suggest that warming of the North Atlantic realm by this mechanism might have substantially delayed ice sheet growth at the end of the Pliocene.