ENSO-like patterns and its driving mechanism in Western Pacific Warm Pool during the glacial cycles

The Western Pacific Warm Pool (WPWP) region affects the global climate change through El Niño-Southern Oscillation (ENSO) and monsoons, as it receives the most solar radiation and has the warmest surface temperature in the world. Abundant sedimentary records indicate WPWP also experienced ENSO-like events throughout geological history. However, the relationships between ENSO and glacial-interglacial cycles or East Asian Monsoon (EAM), as well as the driving mechanism behind ENSO-like patterns, still remain unclear. In this study, we reconstructed the paleoclimate records since Marine Isotope Stage (MIS) 8 by using oxygen isotope, Mg/Ca ratio from planktonic foraminifera, and clay mineral proxy data obtained from sediment core B10 at WPWP. Combined with previously published paleoenvironment records of tropical region, δ18O data of Chinese cave stalagmite, and sea surface temperature records of the Southern Ocean, we studied the evolution of ENSO-like patterns during glacial-interglacial cycles and their relationship with EAM, and discussed the driving mechanism behind ENSO-like patterns. We found that during the glacial period the thermocline in WPWP became shallower, with the temperature gradient decreasing between the Eastern Equatorial Pacific and WPWP. Meanwhile, weakened East Asian Summer Monsoon (EASM) was accompanied by reduced rainfall, similar to modern El Niño. During the interglacial period, the thermocline in WPWP deepened, the temperature gradient along the equatorial Pacific increased, and EASM strengthened with increased precipitation, which was very similar to modern La Niña. Spectral analysis revealed the sea surface temperature in WPWP followed a significant eccentricity cycle (96 ka). During the interglacial period, increasing solar radiation in tropical region increased the latitudinal sea surface temperature gradient, and led to heat accumulation in subsurface water. The accumulated heat in turn regulated heat transfer to WPWP via subsurface circulation and ultimately controlled the long-term changes in the Walker circulation intensity and ENSO-like patterns in equatorial Pacific. During the glacial period, the southeast trade wind and ocean circulation anomalies caused by the cooling of the Southern Ocean might also regulate the ENSO-like patterns. © 2022 Science Frontiers editorial department. All rights reserved.