Cool La Niña During the Warmth of the Pliocene?
R. E. M. Rickaby and
P. Halloran
The role of El NiñoSouthern Oscillation (ENSO) in greenhouse warming and climate change remains controversial. During the warmth of the early-mid Pliocene, we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial Pacific, consistent with the prevalence of a La Niñalike state, rather than the proposed persistent warm El Niñolike conditions. Our Pliocene paleothermometer supports the idea of a dynamic "ocean thermostat" in which heating of the tropical Pacific leads to a cooling of the east equatorial Pacific and a La Niñalike state, analogous to observations of a transient increasing east-west sea surface temperature gradient in the 20th-century tropical Pacific.
Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK.