Solar-forcing-induced spatial synchronisation of the East Asian summer monsoon on centennial timescales

Spatial patterns in centennial-scale variations of the East Asian summer monsoon (EASM) during the Holocene are poorly constrained due to the lack of high-resolution records with detailed chronologies, especially in southern China. Here we present high-resolution (similar to 35-yr) proxy records spanning the last 7500 years from a well-dated sediment core (YJ Core) from the northern inner shelf of the South China Sea. Al, Ti and Fe variations were employed as indicators of terrigenous influx and K/Al ratios were used as a tracer of chemical weathering to document variations in the intensity of the EASM. The results show a series of centennial-scale weak EASM events, which are generally synchronous with those inferred from other geologic archives from monsoonal regions in the eastern and southern China. Moreover, these events are synchronous with periods of weak solar activity, and the spectral analysis demonstrates that the EASM and solar activity share some general cyclicity patterns. We therefore suggest that solar activity is a fundamental driving force for the spatial synchronisation of the EASM on centennial timescales across the monsoon region.