The Evolution Of Indian Summer Monsoon During Mid Holocene Recorded By A High-resolution Stalagmite From Western Yunnan

The Asian monsoon climate system plays a vital role in the globe water vapor and energy cycle.As an important sub-system of the Asian monsoon,the development of India monsoon not only affected by globe climate change,but also responded to global climate change.Holocene is the period of human being,which is the warmest climate since the last interglacial.The feature of Holocene is mild and stable,Especially,the Holocene optimum is the warmest and humid period of Holocene,but there are also a series of centennial-millennial weak monsoon events,The 8.2ka BP climate change event of early Holocene has the most extensive influence.The study of the Holocene palaeoclimatic record of Indian monsoon region will help to better understand the evolution characteristics of the Indian monsoon and its weak monsoon envents.In this paper,the stalagmite of Sigangli Cave in the southwest of Yunnan province in typical Indian monsoon region was selected as the object of study.By using U/Th dating and oxygen isotope measurements(16230Th ages and 1038 oxygen isotope data),we reconstructed a time series of Indian summer monsoon variability from 5.4 to 8.9 ka BP with an average resolution of 3.7 years,analyzed the development of Indian summer monsoon and the 8.2ka BP climate change event during the Holocene optimum,also discussed the possible driving factors of climate change in this period.The main conclusion are as follows(1)The Variability of The Sigangli Cave ?18O records is explained to be a proxyindex of IASM.Overall,these ?18O profiles appear to be a remarkable change on millennial timescale.The overall change trend of the stalagmite ?18O records was positive,indicating that the Indian monsoon gradually became dry,consistent with the law that the monsoon gradually weakened since the mid-Holocene.(2)By comparing the record of Sigangli Cave stalagmite and other stalagmites inthe Asian monsoon region,it shows that the Asian monsoon subsystems in the Holocene optimum is synchronous.On the orbital scale,The evolution of the Indian monsoon is mainly controlled by the changes of solar insolation in the northern hemisphere.(3)The ?18O records clearly captured the 8.2ka BP climate change event,itoccurred at about 8.31?8.1ka BP The process of change is characterized by a slow start and a relatively sudden end.Analying the change trend of ?18O curves and comparing with the Greenland ice core records,we found that the SGL1220 records basically consistent with the Greenland ice core records within the scope of error.It shows that the Indian monsoon climate is coupled with the northern latitude climate,The climate of the Indian monsoon region is teleconnected with the North Atlantic climate.Compared with the high resolution stalagmite records in the Asian monsoon area,we found that the overall trend of the three records is the same,but there are still differences in the internal structure,fluctuation amplitude and duration of events.The difference may be due to the discrepancy in dating errors or the regional climate response.(4)SGL1220 records are basically consist with the north latitude climate records,solar radiation and Ti content in Cariaco Basin.Spectral analysis on the stalagmite ?18O records reveal that exist?1155??693??20??11 year cycles,which are generally consistent with the solar activity cycle.These periodicities reveals that Indian summer monsoon climate change is directly driven by solar activity.It supports the driving forces that solar radiation affect the north-south movement of ITCZ through the tumble flow in the North Atlantic,thus affecting the strength of the Asian monsoon.