Eocene monsoon prevalence over China: A paleobotanical perspective

Proxy-based quantitative estimates of Eocene climates can be made from marine isotope records for ocean conditions or fossil plants for terrestrial environment. However, our understanding about Eocene terrestrial climates is derived mainly from North America and Europe, and little is known about East Asia. Previous qualitative paleoclimate studies briefly revealed three climatic regimes across China during the Eocene with a planetary wind-dominated subtropical to tropical arid zone in the central part (i.e., the subtropical highs), which was flanked by the subtropical climate zone in the north and tropical climate zone in the south. But such a pattern of paleoclimatic zonation still requires a test from quantitative study. Based on analyses of 66 plant assemblages, carefully selected from 37 fossil sites throughout China, we here report the first large-scale quantitative climatic results and discuss the Eocene climatic patterns in China. Our results demonstrate that the Eocene monsoonal climate must have been more or less developed over China, judging from the presence of apparent seasonality of both temperature and precipitation revealed by our quantitative estimation. This appears not to support the previously claimed Eocene planetary wind-dominated climate system, at least in the region of eastern China. In addition, the research indicates that, with a slight declining trend of MAT during the Eocene, the winter temperature substantially dropped in tropical southern China during the middle to late Eocene interval. This might be related to the development of a weak Eocene Kuroshio Current in the southwestern Pacific, and/or a significantly enhanced paleo-winter monsoon from Siberia. ► We quantitatively calculated the Eocene terrestrial climates of China. ► Seasonal climate changes over the country indicate the development of Eocene monsoon. ► Mean annual temperature of the tropics slightly declined throughout the Eocene. ► Dramatic drop of winter temperature of the tropics occurred in the late Eocene.