Weakening of the South Asian summer monsoon linked to interhemispheric ice-sheet growth since 12 Ma

Abstract

The evolution and driving mechanism of the South Asian summer monsoon (SASM) are still poorly understood. We here present a 12-Myr long SASM record by analyzing the strontium and neodymium isotopic composition of detrital components at IODP Exp. 359 Site U1467 from the northern Indian Ocean. The provenance investigation demonstrates that more dust enriched in ?Nd from northeastern Africa and the Arabian Peninsula was transported to the study site by monsoonal and Shamal winds during the summer monsoon season. A two-step weakening of the SASM wind since ~12?Ma is proposed based on the ?Nd record. This observational phenomenon is supported by climate modeling results, demonstrating that the SASM evolution was mainly controlled by variations in the gradient between the Mascarene High and the Indian Low, associated with meridional shifts of the Hadley Cell and the Intertropical Convergence Zone, which were caused by interhemispheric ice-sheet growth since the Middle Miocene. The ?Nd record from the IODP Exp. 359 Site U1467 in the northern Indian Ocean, along with climate modeling, reveals a two-step weakening of the South Asian summer monsoon (SASM) wind since 12?Ma. The SASM evolution was mainly caused by interhemispheric ice-sheet growth since the Middle Miocene.