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 εNd 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 εNd 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.

南亚夏季风 (SASM) 的演变和驱动机制仍然知之甚少。我们在这里通过分析 IODP Exp 碎屑成分的锶和钕同位素组成，展示了 12 Myr 长的 SASM 记录。359 来自印度洋北部的 U1467 站点。来源调查表明，在夏季季风季节，来自非洲东北部和阿拉伯半岛的更多富含 εNd 的尘埃被季风和沙马尔风输送到研究地点。根据 εNd 记录，提出了自 ~12 Ma 以来 SASM 风的两步减弱。这种观测现象得到了气候模拟结果的支持，表明 SASM 的演变主要受马斯克林高地和印度低地之间梯度的变化控制，