Millennial-scale Abrupt Event In The MIS3/2 Transition Period Recorded By Stalagmite From Xianyun Cave, Fujian Province

The last glacial climate change was characterized by abrupt,millennial-scale climate change,with the Dansgarrd-Oeschger event?DO event?and the Heinrich event?H event?being the most significant.Among them,the MIS3/2 transition period is the focus of paleoclimate change research.With the emergence of high-resolution geological records,the research on the MIS3/2 transition period is increasingly rich.However,the previous stalagmite research on this period mainly comes from the middle and lower reaches of the Yangtze River and the southwestern of China,and due to the problem of sample resolution,the phase relationship between the low-latitude monsoon and the rapid change of the north latitude in the MIS3/2 transition period is still vague,especially in the southeastern of China.This study selects the Xianyun Cave stalagmites in Fujian Province,which is affected by the typical East Asian summer monsoon in southeastern of China.The high-resolution ²³⁰Th dating and high-resolution carbon and oxygen isotope test analysis establishes the high resolution of the MIS3/2 transition period in this area.The oxygen isotope sequence provides record support for studying the spatial comparison of East Asian summer monsoon records during this period.On this basis,comprehensively compare the paleoclimatic records of other regions,and explore the evolution characteristics and driving mechanism of the East Asian monsoon occurring during the H events and DO events.Based on 17 ²³⁰Th dating data and 765 oxygen isotope data of XYIII-28 stalagmite in Xianyun Cave,the stalagmite?¹⁸O with an average resolution of 15 yr during34.52²2.92 kyr B.P.was established according to linear interpolation and extrapolation.The following of the XYIII-28 stalagmite?¹⁸O record analysis.?1?The variation range of XYIII-28 stalagmite?¹⁸O during the period from 34.52 to22.92 kyr B.P.was-7.92^-6.08‰,and the overall amplitude was 1.84‰.The XYIII-28stalagmite has a sedimentary discontinuity in the three periods of 33³1.8 kyr B.P.,27.9²6.3 kyr B.P.and 30.7⁹.7 kyr B.P..Therefore,the whole XYIII-28 stalagmite?¹⁸O sequence is divided into four stages,in which the evolution of DO4 event and H2 event are completely recorded in the third stage and the fourth stage respectively.?2?Comparing the records of the stalagmites in Xianyun Cave with other records of ice core,stalagmites,marine sediment and solar radiation in the MIS3/2 transition period,it is found that the monsoon evolution recorded by the?¹⁸O of the stalagmites in Xianyun Cave is different from the orbital scale.The stalagmite records of Hulu Cave,Yongxing Cave,Sanbao Cave,Wulu Cave and Dashibao Cave have obvious positive trend,which may indicate that stalagmite records located in the middle and lower reaches of the Yangtze River and the southwestern of China may be affected by 30^oN?June?.The influence of driving factors such as solar radiation,and the stalagmites recorded in Xianyun Cave in the southeastern of China is characterized by a low latitude climate.?3?The start and end times of H2 event and H2.1 event recorded by stalagmite XYIII-28 are 24.09²3.39 kyr B.P.and 24.97²5.62 kyr B.P.,respectively,which can be recorded with Greenland ice core GISP2 within the range of dating error.Other stalagmite records in the Asian monsoon region have a good correspondence.In addition,the H2event and the H2.1 event recorded in the high-resolution XYIII-28 stalagmite?¹⁸O have very obvious"two valleys and one peak"sub-cycle structure,which may indicate a relatively cold millennium scale climate.The climatic state within a abrupt event may also manifest itself as an unstable climatic state.?4?The start and end time of DO2 event and DO4 event recorded by Xianyun Cave stalagmite XYIII-28 are 23.39²3.22 kyr B.P.,28.83²8.46 kyr B.P.,respectively,and can be recorded with Greenland ice core and Asian monsoon region within the error range of dating.Other stalagmite records have a good correspondence.The high-resolution XYIII-28 stalagmite?¹⁸O record clearly records the H2/DO2 transformation characteristics.The DO4 event recorded by the XYIII-28 stalagmite?¹⁸O in Xianyun Cave is characterized by a“slow start,faster end”feature,which is different from the high-resolution stalagmite?¹⁸O record previously published in the Chinese monsoon region.Perhaps hydrothermal reorganization activities in low latitudes should be given more attention in the exploration of monsoon driving forces.