How old is the Asian monsoon system?—Palaeobotanical records from China

Abstract

The recent discovery of monsoon records in early Miocene raised a question of the time when the East Asian monsoon system initiated. A distinguishing feature of the modern monsoon system is its geographic distribution which disturbs the zonal pattern indigenous to the planetary climate system, and the appearance of the monsoonal climate pattern in the geological records should signify the onset of the monsoon system. Here we present the results of a compilation of palaeobotanical and lithological data from 125 sites over China, that has revealed two completely different patterns of climate zones: the Palaeogene pattern with a broad belt of aridity stretched across China from west to east, and the Neogene pattern with the arid zone restricted to northwest of China which has persisted until today. The reorganization of the climate system around the Oligocene/Miocene boundary provides evidence for the establishment of the modern East Asian monsoon. Since then, the Neogene has witnessed significant variations of the monsoon system, including enhancement of aridity and monsoon intensity at about 15–13 My, around 8 My and 3 My. The new data do not support the onset of the Asian monsoon system around 8 My. Rather, the new data led to a hypothesis that the transition to the monsoon climate system in East Asia occurred in the latest Oligocene.