Changes In Indian Summer Monsoon Over The Last Thousand Years Recorded By High-resolution Stalagmites From Western Yunnan,China

Indian monsoon?also known as southwest monsoon?is an essential component of the Asian monsoon system and the primary source of precipitation in southwest China.Therefore,Indian monsoon is crucial to the development of social economy and the ecological environment in this region.The change and driving mechanism of summer monsoon?precipitation?over the past thousand years is an essential reference for assessing regional future precipitation response under the background of global warming.There are many reconstructed records of Indian summer monsoon over the past thousand years,but there are still many divergences in understanding its evolutionary characteristics and driving mechanism.The reason is that the sample has a large age error,fewer existing records,and insufficient resolution.About recent thousand years of the high-resolution stalagmites recorded are seldom distributed from Yunnan in China,especially in the typical Indian monsoon area in western Yunnan.Choosing this area as the research area can make up for the deficiency of climate records in Indian monsoon area,furthering understand the evolution characteristics of Indian monsoon area about the century-decadal scale in recent thousand years,predict the future climate change in this area and provides a scientific basis.Based on 21 ²³⁰Th ages and 813 oxygen isotope data from two stalagmites SGL1and SGL4 in Sigangli Cave,Yunnan Province,this paper reconstructs the evolution process of Indian summer monsoon over the past 1400 years in southwestern China and discusses its possible driving mechanism.The main conclusions are as follows:?1?The oxygen isotope of stalagmites in Sigangli Cave reflects the variation of the intensity?amount?of Indian summer monsoon?precipitation?.The oxygen isotope time series of stalagmites SGL1 and SGL4 reconstructed the summer monsoon precipitation change about the past 1400 years in this area.The oxygen isotope of stalagmites SGL4showed significant interdecadal fluctuation characteristics.?2?At the century scale,the oxygen isotope of SGL4 stalagmites recorded the process of climate change from strong to weak in the Medieval Warm Period to Little Ice Age in Indian summer monsoon.Compared with other high-resolution stalagmite records in the same monsoon area,the oxygen isotope variation of SGL4 stalagmites in Sigangli Cave of Yunnan Province is consistent with the oxygen isotope records of Qunf Cave,Sahiya Cave,Jhumar-Dandak Cave and Shenqi Cave,but the trend is opposite in1300-1400AD.?3?At the interdecadal scale,four significant weak monsoon events?1010-1098AD,1280-1330AD,1600-1730AD,1750-1830AD?have similar fluctuations with those in the Jhumar-Dandak Cave,but have significant differences with other oxygen isotope records of stalagmites in the Indian monsoon region.It is believed that these events may be the result of precipitation,which shows that summer monsoon precipitation of spatial variability in the northwest,central and northeastern regions of India and the southwest of China.?4?Comparing the oxygen isotope records of the Sigangli Cave and the East Asian Summer Monsoon?EASM?area in the Sigangli Cave and the East Asian Summer Monsoon?EASM?in the Indian monsoon region,we can find the monsoon trend in the western Yunnan and East Asian summer monsoon regions in the past millennium.Generally consistent,and similar in the century-decadal scale.?5?The SGL4 of stalagmites in Sigangli Cave has recorded the detailed process from warm and wet to cold and dry during the Indian summer monsoon from Medieval Warm Period to Little Ice Age,and recorded the weak monsoon events in different degrees during the minimum solar activity period.Combined with power spectrum analysis and compared with the reconstructed solar activity record(TSI,¹⁰Be),Northern Hemisphere temperature change?NH-temp?record and ENSO index,We consider solar activity to be the main driver of the Indian summer monsoon in the last thousand years.