Southward Shift and Intensification of the Intertropical Convergence Zone in the North Pacific Across the Mid-Pleistocene Transition

The Hadley Circulation and associated westerlies strengthened and moved equatorward across the mid-Pleistocene transition (MPT). However, the evolution of the intertropical convergence zone (ITCZ) is still elusive due to the scarcity of long-term hydrological records from regions sensitive to the ITCZ change. Here, high-resolution sea surface salinity estimates derived from surface-dwelling planktic foraminiferal delta 18O and Mg/Ca in Ocean Drilling Program Site 871 reveal a long-term freshening trend in the central equatorial Pacific across the MPT. We attribute this secular reorganization of the precipitation-evaporation balance to the gradual southward migration and intensification of ITCZ in the North Pacific. It is inferred that the long-term evolution of the ITCZ was modulated by the increased meridional sea surface temperature gradients and the enhancements of trade winds across the MPT.