Reappraisal of Eocene climate patterns in East Asia: A synthetic review

Proxy-based reconstructions and modeling studies have long yielded conflicting patterns for the Eocene East Asian climate, hindering a coherent understanding of its dynamics. The recent discovery of Eocene monsoon-arid climate signatures has reignited debates regarding the spatiotemporal origins and drivers of this system. To resolve these discrepancies, we undertake a synthesis of multi-proxy paleoclimate records from 71 key Eocene sites across China to systematically reevaluate the spatiotemporal evolution of climate patterns in southern, central, and northern China. Our analysis delineates three distinct climatic phases: (1) During the early Eocene, a zonal broad arid-semiarid belt extended across central-southern China (20–40°N), flanked by two humid zones in Hainan Island-southern Tibet (<20°N) and northern China (>40°N), respectively; (2) Subsequently, by the middle Eocene, a humid monsoonal climate advanced northward in southern China (<25°N), while central China remained persistently arid and northern China maintained its humid conditions; (3) During the late Eocene, the humid monsoonal climate in southern China expanded further northward (26–28°N), the eastern part of central China experienced intermittent humid intervals, the western part of central China (northwest China) underwent pronounced aridification, and northern China witnessed a southward expansion of its humid zone into the Bohai Bay Basin. A pivotal climatic reorganization occurred at 41 Ma, characterized by the synchronous intensification of the Asian monsoon in southern China and aridification of the Asian interior, marking the inception of the Asian monsoon-arid system. This study reconciles long-standing inconsistencies by demonstrating that middle–late Eocene humidification in southern China was primarily driven by the intensification of the East Asian (EAM) and South Asian (SAM) monsoons, rather than primarily by latitudinal migrations of the Intertropical Convergence Zone (ITCZ). Central China was predominantly under the influence of subtropical high pressure throughout the Eocene, with episodic monsoonal incursions limited to the late Eocene. Conversely, the hydroclimate of northeast China was predominantly governed by westerlies transporting moisture from the proto-Paratethys Sea, rather than by the EAM. We propose that the evolution of Eocene climate patterns was driven by the combined effects of Tibetan Plateau uplift, the retreat of the proto-Paratethys Sea (a key driver of the climatic shift at 41 Ma), and global cooling. Our findings establish an integrative framework linking tectonic forcing and global change to East Asia's paleoenvironmental evolution, offering pivotal insights into the origins of the modern Asian climate system.