The Sichuan Stalagmite Record Of The Variability Of The Asian Monsoon Over A Century-decadal Period In 200

The study about the Asian monsoon variability on centennial-decadal scale and its driving mechanism during the past 2,000 years has become a key area in the study of modern climate.Due to the lack of high-resolution geological records with presice dating,the frequency,amplitude and pattern included in the abrupt change of monsoon are still unclear.In this paper,we reconstruct a high resolution Asian monsoon sequence from 230 BC to 1825 AD based on 29 230Th ages,857 groups of oxygen and carbon isotope data of three stalagmites in Heizhugou cave,E'bian province,Sichuan County.The time series covers four typical climate periods including the Rome Warm Period,Dark Ages Cold Period,Medieval Warm Period and the Little Ice Age Period.And the monsoon intensity presents the progress of stronger-weaker-stronger-weaker.Comparing EB ?18O sequence of the stalagmite in Heizhugou Cave with other stalagmite records in Asian monsoon region,we can see that the overall trend of the?18O sequences are consistent on century scale,implying that stalagmite ?18O in Asian caves is controlled by the same climatic factor,which can better reflect the regional change of Asian monsoon precipitation.However,the difference between the ?18O sequences on centennial-decadal scale indicates that ?18O signal may be affected by several factors,such as the difference of share ratio of water vapor source,the spatial difference of monsoon rainfall and so on.Significant 9?11 a,20?25 a cycles in the EB1 and EB5 ?18O sequences are respectively shown by spectral analysis,equivalent to 11 a and 22 a sunspot cycle.The power spectrum and wavelet analysis of EB5 stalagmite record both present 80?100 a variation period,including the Gleissberg cycle of?80 a and the Century cycle of?100 a.The record of stalagmite EB5 is generally consistent with solar activity indicators.And the two events named Late Acient Little Ice Age(LALIA)and Little Ice Age(LIA)correspond well to volcanic eruptions.It reveals that the intensity of Asian monsoon is controlled by the common influence of solar and volcanic activity on short scale.Volcanic eruption may be its triggering mechanism and solar activity is the maintain mechanism.The 8]80 sequence of the stalagmite EB1 clearly records the characteristics of high frequency oscillations during the Little Ice Period(1375?1810 AD).Significant weak monsoon stage at the end of 16th century has become the most severe drought period in the past 500 years in China.The ?18O profile is positively correlated with North Hemisphere temperature.This result further indicates that the Asian monsoon might respond quickly to the climate change of northern high latitude in the period.