Suppression of El Niño during the Mid‐Holocene by changes in the Earth's orbit

Abstract

A number of recent reports have interpreted paleoproxy data to describe the state of the tropical Pacific, especially changes in the behavior of the El Niño‐Southern Oscillation (ENSO), over the Holocene. These interpretations are often contradictory, especially for the eastern tropical Pacific and adjacent areas of South America. Here we suggest a picture of the mid‐Holocene tropical Pacific region which reconciles the data. ENSO variability was present throughout the Holocene but underwent a steady increase from the mid‐Holocene to the present. In the mid‐Holocene, extreme warm El Niño events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial Pacific and largely arid coastal regions as in the present climate. This picture emerges from an experiment in which a simple numerical model of the coupled ocean‐atmosphere system in the tropical Pacific was driven by orbital forcing. We suggest that the observed behavior of the tropical Pacific climate over the mid‐ to late Holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics, which dominates extratropical influences.