Southern hemisphere monsoonal system during superinterglacial stages: MIS5e, MIS11c and MIS31

Abstract

The current study investigates changes in Austral Summer Monsoon based on numerical experiments conducted with the coupled ICTP-CGCM model. The interannual variability and intensity of the monsoonal system have been analyzed from vorticity indices and air-sea interaction in Africa, Australia and South America. We focus on interglacial stages MIS5e (127 ka), MIS11c (409 ka) and MIS31 (1072 ka). Results show orbitally-driven decreased summer precipitation and slightly shifted monsoon onset and demise with respect to present day conditions. Sensitivity experiments indicate that monsoons are forced not only by the dominant effect of insolation, but also by remote teleconnections, such as the equatorial Atlantic and Pacific ocean basins. During those interglacial stages, cooling occurs in the Southern Hemisphere whereas Northern Hemisphere substantially warms. This induces meridional displacement of oceanic subtropical high pressure systems and the equatorial convergence zone. Regionally, these mechanisms contribute to droughts over the Amazon and northeastern Brazil, northern Australia and southern Africa. Monsoonal rainfall shows different responses to precessional forcing, as well as the relationship between the monsoon and Niño 3.4 differs among the interglacial stages. Results also indicate a weaker influence of the equatorial Pacific Ocean on the Austral summer monsoon for the MIS31 interglacial stage as compared to current climate conditions across Africa and Australia. On the other hand, South America monsoon is strongly influenced by Niño 3.4 and tropical Atlantic.