Assessing the impact of mid-Holocene insolation on the atmosphere-ocean system

A sequence of numerical simulations was performed in order to assess the role of early- to mid-Holocene orbital forcing on the coupled atmosphere-ocean system. Results from both an atmosphere-only general circulation model (GCM) forced by specified sea surface temperatures and a coupled atmosphere-ocean GCM consistently suggest a stronger south Asian monsoon and a strengthened Pacific Walker circulation. The latter feature interacts dynamically with the equatorial ocean in the coupled model to produce enhanced Pacific upwelling, a more pronounced cold tongue, and an even stronger monsoon. Results suggest that the climate of the equatorial Pacific was more similar to the La Nina phase of the modern Southern Oscillation rather than the El Nino phase.