Evolution Of Asian Summer Monsoon During The Last 1500 Years Recorded By High-Resolution Stalagmite From Shijiangjun Cave,Guizhou

Climate change is closely related to the living environment of human beings,the development of the world economy and the progress of society.Under the influence of global warming,extreme climate events will become more frequent,which will profoundly affect people's life and social development.The Asian monsoon can be regarded as a key link connecting the global high-middle-low latitude climate change and is an important part of the global climate system.Due to the influence of the Asian summer monsoon,the alternation of drought and flood disasters in Southwest China is frequent,which has a profound impact on the ecological environment and socio-economic development.Southwest China is a well-known karst landform area in China and even in the world,with karst caves widely distributed.However,Southwest China was far away from the traditional political and economic centers.The historical documents of Southwest China are scarce,especially historical documents on climate,which have caused many inconveniences to the researchers of palaeoclimate.In addition,modern monitoring records are too short to accurately reflect climatic factors and environmental changes in a particular area.Therefore,we reconstructed the climate change during the past 300-1800 A.D by using high-precision dating and high-resolution multi-index records of stalagmite SJJ-300 from Shijiangjun Cave in Guizhou,Southwest China.It is of significance to understand the complexity of climate change,the ecological evolution of karst areas and the prevention of drought as well as flood disasters in the future in southwest China.The main conclusions of this research are as follows:(1)During the Little Ice Age,the?¹⁸O record of SJJ-300 stalagmite indicted six significant weak summer monsoon events:1340-1380,1445-1480,1520-1540,1600-1630,1650-1670 and 1695-1730 A.D,which basically corresponded to the weak summer monsoon events recorded in the Dandak and Jhumar caves in India.Furthermore,on the decadal to centennial time scale of the Little Ice Age,the Asian summer monsoon recorded by SJJ-300 stalagmitic?¹⁸O and the Indo-Australian summer monsoon recorded by Dandak and Jhumar cave in India showed a consistent weakening trend.It was inconsistent with the"see-saw"pattern in the northern and southern Hemispheres,indicating that the Asian summer monsoon and Indo-Australian summer monsoon were controlled by the same climate system.During the Little Ice Age,the low temperature in the Northern Hemisphere and the positive phase of PDO and ENSO weakened the Asian-Australian summer monsoon and reduced the precipitation in the entire Asian-Australian monsoon region.(2)The?¹⁸O and?¹³C records of SJJ-300 stalagmite showed a positive correlation from 300 to 1800 A.D,and the overall change trend of them was consistent.The?¹⁸O and?¹³C records of SJJ-300 stalagmite in the period 300-900 A.D showed good co-variability,and the response of oxygen and carbon isotopes to climate change was synchronous.During the Medieval Warm Period(1000-1200 A.D),the values of?¹⁸O in stalagmite SJJ-300 gradually turned negative and ASM increased.However,the values of?¹³C in the stalagmites from Shijiangjun Cave and Furong Cave showed a gradually positive trend,which indicated that the main factor affecting the ecological environment change in this region during 1000-1200 A.D was not the climate conditions,but human activities.The?¹³C record of SJJ-300 stalagmite was more positive after 1300 A.D of Little Ice Age.The decrease of temperature,the weakening of ASM and the enhancement of human activities may further aggravate the process of rocky desertification in the karst area of Southwest China.(3)Trace elements,as one of the important indicators of paleoclimate reconstruction,can used to analyze and restore the information of past climate change.During the period of 300-1800 A.D,the Mg/Ca and Sr/Ca records of SJJ-300 stalagmite were negatively correlated(R=-0.16,P<0.05).The overall change trend of Mg/Ca and Sr/Ca records was in reverse phase,indicating that Mg/Ca and Sr/Ca records were controlled by different climate driving factors.(4)Compared to the Medieval Warm Period,the coastal region of southeast-south China mainly showed a"cold-wet"pattern over the LIA.The south flank of the Qinling Mountains and the alpine forest region of Shennongjia mainly showed a"cold-wet"pattern.Affected by Indian summer monsoon,East Asian summer monsoon and complex terrain,the climate change in southwest China experienced discrepancy during the LIA,without presenting a relatively consistent and typical climate pattern.Due to the number of records,the uniformity of spatial distribution,the sensitivity to climate response,dating method,dating error and resolution,there is a certain degree of uncertainty in the reconstruction of climate model.Therefore,in the reconstruction of paleoclimate in South China on the decadal-centennial time scale,it is particularly important and urgent to cover more areas with high-precision and high-resolution records.