ENSO-like evolution of the tropical Pacific climate mean state and its potential causes since 300ka

The tropical Pacific Ocean plays a significant role in climate change, and the El Niño-Southern Oscillation (ENSO) is considered to be closely related to extreme climate phenomenon worldwide. However, the evolution of the ENSO-like patterns in the tropical Pacific during the Pleistocene glacial cycles remains controversial. In this study, we present geochemical indices and a transient model simulation to explore the ENSO-like evolution during the glacial-interglacial cycles and its driving mechanisms. Our results indicate that during the interglacial periods, the Western Pacific Warm Pool (WPWP) is characterized by the modern El Niño-like conditions with relatively decreased precipitation and weakened East Asian Summer Monsoon (EASM). By contrast, the mean state of WPWP during glacial periods is more similar to the modern La Niña-like conditions, with increased precipitation and the intensified of EASM. Spectral analyses showed that the WPWP hydrodynamics were controlled by the earth's orbital parameters through their impacts on ocean circulations. Combined with published data, we find that expansion of water masses formed in the Southern Ocean would change the deep-water redox conditions, subsurface water upwelling and surface productivity in the WPWP, and ultimately influence the ENSO-like conditions through CO2-related Walker Circulation on glacial-interglacial cycles.