ENSO‐Like Modulated Tropical Pacific Climate Changes Since 2.36 Myr and Its Implication for the Middle Pleistocene Transition

Abstract

AbstractEl Niño/Southern Oscillation (ENSO) activity and the Pacific Walker Circulation are controlled by the zonal sea surface temperature (SST) gradient between the western and Eastern Equatorial Pacific (EEP) and the corresponding barometric difference. Variations in the zonal SST gradient since the early Pleistocene have primarily been triggered by changes in the SST in the Eastern Equatorial Pacific. However, the response of the ENSO‐like long‐term state to the cooling of the EEP and its coupling role with tropical Pacific climate changes are still not well established. Here we present a high‐resolution grain‐size record spanning the last 2.36 Myr, obtained from marine core sediment located in the West Philippine Sea in order to decipher the tropical pacific climate changes and reveal its controlling mechanism. By combining our data with other long‐term climatic records from the Equatorial Pacific, we demonstrate that the cooling of SST and enhanced upwelling in the EEP resulted in the development of the Walker Circulation and increased monsoon precipitation in Luzon from 2.2 to 1.6 Myr, from 1.2 to 0.8 Myr, and since 0.2 Myr ago. The progressive cooling of the high‐latitudes in the Quaternary may be responsible for our observation here. A newly identified 100 kyr dominant period between 2.2 and 1.6 Myr in the ENSO‐like modulated Pacific climate records indicates that the ENSO‐like system may play a key role in facilitating or responding to the global climate changes.