Simulation of the 9.2-ka BP Weak Asian Summer Monsoon Event

A series of abrupt Asian monsoon events occurred in the Holocene epoch. One such event, a weak monsoon event that took place approximately 9.2 ka ago, has received less attention, and its existence, as well as its underlying genetic mechanisms, remain subjects of debate. In this paper, we present the results (Nanjing Normal University-12ka; NNU-12ka) obtained from a Holocene transient integrated climate simulation test using the Community Earth System Model. We compared the reconstruction data with the Transient Climate Evolution over the last 21,000 years (TraCE-21ka) to explore the spatial and temporal characteristics of the 9.2-ka Asian weak monsoon event and understand its causes. Our primary findings are the following: The solar activity sensitivity test of NNU-12ka reveals a weak Asian monsoon event around 9.6～9.4 ka. During this period, total solar radiation decreased by 0.38 W m⁻², resulting in average summer precipitation in the Asian monsoon region decreasing by 0.17 mm per day. However, our comprehensive forcing test based on TraCE-21ka indicates that glacier meltwater and changes in ice cover did not significantly affect the Asian monsoon during this period. In the NNU-12ka solar activity test, summer precipitation in the Asian tropical monsoon region decreased significantly, while precipitation in Northeast China increased slightly. The weakening of the tropical monsoon is attributed to a sudden drop in solar radiation, which reduced the temperature difference between the land and sea. This led to an increase in Asia’s sea-level pressure, causing abnormal subsidence in the tropical monsoon region. Consequently, the transmission of water vapor to the Asian monsoon region was suppressed, resulting in a weakened monsoon through a dynamic process.