As a crucial part of the Asian monsoon stretching from tropical India to temperate East Asia, the Indian monsoon (IM) contributes predominant precipitation over Asian continent. However, our understanding of IM’s onset, development and the underlying driving mechanisms is limited. Increasing evidence indicates that the IM began in the Eocene or even the Paleocene and was unexceptionally linked to the early rise of the Tibetan Plateau (TP). These were challenged by the heterogeneous and diachronous uplift of the TP and all the reported records were confined to tropical zone under tropical monsoon driven by the Intertropical Convergence Zone (ITCZ) that is irrelevant to the TP. Therefore, reliable paleoclimatic records from the extra-tropical IM region is crucial to reveal how the tropical IM expanded to subtropical and temperate zones and what driving factors might be related to it. Here we present robust Eocene paleoenvironmental records from central Yunnan (~26°N) in subtropical East Asia. The multiproxy results of two sites demonstrate a consistent sudden switch from a dry environment in the early Eocene to a seasonally wet one at 41 Ma, suggesting a jump of the tropical IM to the southern subtropical zone at 41 Ma. The full collision of India with Asia, and the resulting changes in paleogeography at 41 Ma (closure of the Neotethys sea, retreat of the Paratethys seas, fast northward movement of the southern margin of the TP and rise of the central TP), aided by synchronous Antarctic cooling, might have worked together to drive the IM enhancement and northward expansion.

作为从热带印度延伸到温带东亚的亚洲季风的重要组成部分，印度季风（IM）贡献了亚洲大陆的主要降水。然而，我们对 IM 的发生、发展和潜在驱动机制的了解是有限的。越来越多的证据表明 IM 始于始新世甚至古新世，并且与青藏高原 (TP) 的早期崛起毫无例外地相关联。这些受到了 TP 的异质性和历时隆升的挑战，所有报告的记录都局限于热带季风下的热带地区，该热带季风由与 TP 无关的热带辐合带 (ITCZ) 驱动。所以，来自温带 IM 区域的可靠古气候记录对于揭示热带 IM 如何扩展到亚热带和温带以及可能与之相关的驱动因素至关重要。在这里，我们展示了亚热带东亚云南中部 (~26°N) 的始新世古环境记录。两个站点的多代理结果表明，从始新世早期的干燥环境突然转变为 41 Ma 的季节性潮湿环境，表明热带 IM 在 41 Ma 跃迁至南亚热带。印度与亚洲的全面碰撞，以及由此产生的 41 Ma 古地理变化（新特提斯海关闭，副提斯海退缩，TP 南缘快速向北移动和 TP 中部上升），由同步南极降温，