Anti-Phase Strengthening of the South and East Asian Summer Monsoons During the Early Pliocene Driven by Southern Hemisphere Ice Volume

The East and South Asian summer monsoons affect billions of people but a multitude of potential variables have precluded definitive attribution of their controlling mechanisms and hindered models of their evolution in an anthropogenically warmed climate. Atmospheric CO₂ concentrations were higher than modern during the early Pliocene and provide a potential analog for future climate. Therefore, understanding East and South Asian summer monsoons during the early Pliocene is instructive to understanding their forcing mechanisms and future variation. Here we report the first evidence for an anti-phasing trend between the East and South Asian summer monsoons during early Pliocene time based on multiple lines of evidence. Comparison of our results with the paleoceanography records suggests that the strengthening of South Asian summer monsoons and weakening of East Asian summer monsoons during the early Pliocene were likely driven by the increase of Antarctic ice volume.