Asynchronous variation in the East Asian winter monsoon during the Holocene

The East Asian winter monsoon (EAWM) is one of the most active components of the global climate system. Climate anomalies associated with the EAWM differ between extratropical and tropical regions due to the EAWM's meridional extent. Spatial differences in the EAWM variability on centennial and millennial time scales during the Holocene have not been well understood. This study describes Holocene spatiotemporal features of the EAWM based on comparisons of proxy records and climate simulations. The analysis specifically compared four proxy records located throughout China to assess the EAWM's spatial variability during the Holocene. These records indicate a stronger EAWM during the early Holocene than that during the late Holocene. The EAWM also shows a rapid, asynchronous decline from northwestern to southeastern China. The EAWM declined in northwestern China from 10 to 7.5 ka B.P., whereas the decline did not occur in southern China and the eastern Tibetan Plateau until 6–4.5 ka B.P. Coupled equilibrium and transient simulations of climate evolution during the Holocene indicate that the decline of the EAWM from 10 to 7.5 ka B.P. was probably caused by melting of Northern Hemisphere (NH) ice sheets and enhanced Atlantic meridional overturning circulation (AMOC). The decline of the EAWM from 6 to 4.5 ka B.P. over the eastern Tibetan Plateau and southern China is related to an abrupt increase in sea surface temperatures (SSTs) of the tropical western Indian Ocean. We therefore argue that the regional shift in EAWM intensity was probably related to a distinguishing response to high-latitude (NH ice sheets and AMOC) and low-latitude (tropical SSTs) forcings