A Stalagmite Record Of The Evolution Characteristics Of The East Asian Monsoon On A Millennium-decadal Scale

Studying the extent and method of the Asian monsoon's response to global climate change events on the millennial to century timescale is extremely important for understanding the relationship between the Asian monsoon and high and low latitude climate changes in the northern and southern hemispheres and the dynamic mechanism of the evolution of the Asian monsoon.The study of Asian monsoon changes on multidecade timescale has important application value for understanding the short-term climate evolution law and realizing the prediction of modern climate change,especially in the context of global warming,frequent natural disasters,the study of the Asian monsoon climate variability on multidecade timescale is even more significant.Based on the stalagmite LS46 of Luoshui Cave and YX108 of the annual layer stalagmite in Yongxing Cave,Hubei,this paper reconstructed the evolution of the Asian monsoon at 24.16-0.39 ka B.P.and 123.24-121.22 ka B.P.,respectively.The stalagmite LS46 completely covered the Last Glacial Maximum?LGM?with the largest amount of ice,the Last Deglacial with the rapid melting of ice and the minimum amount of ice during the Holocene Warm Period,there are 17 age controls for the entire stalagmite,with an average resolution of 14 years.It has completely recorded the millennial and centennial-scale events since the LGM.Stalagmite YX108 is 1840 mm in length,the whole stalagmite has a fast growth rate?about 1 mm/a?,the growth layer is clear,there are 4 absolute age controls,and average resolution is 1 a,which makes it possible to study the multidecades-scale variability of the Asian monsoon at the Last Interglacial period.Based on the unique growth period and resolution advantages of the two samples,this paper combines the two records in order to study the climate evolution characteristics of the Asian monsoon on different time scales.On the millennial time scales,we used the Rampfit method to comparatively analyze the relative amplitudes of Hs1,YD,8.2ka,and 4.2ka events recorded by stalagmite LS46 under different ice backgrounds.The results show that the amplitude of the YD event is about 1/2-2/3 of Hs1,which is twice the amplitude of the 8.2ka event.The amplitude of the 8.2 ka event is slightly higher than the 4.2 ka event.The ratio of the two is approximately 1:1.In the absence of high-resolution and continuous records,we used the stalagmite LS1 with the same growth period to analyze the amplitude relationship between Hs1 and YD and the 8.2ka and 4.2ka of DA to verify our results.The amplitude relationship of the events recorded by the two stalagmites on the millennial scale also supports our conclusion.On the centennial time scale,the stalagmite LS46 clearly recorded several weak monsoon events on the centennial time scale during the mid-late Holocene.These weak monsoon events have a good correspondence with the stalagmite DA,indicating that the Asian monsoon recorded by the stalagmite LS46 has regional consistency on the centennial time scale;In addition,stalagmite LS46 also recorded five centennial-scale anomalous negative?¹⁸O periods.The amplitude of these strong monsoon events exceeded 0.5‰and the average duration was about 500 a.the stalagmite DA with higher resolution had a weak response to the strong monsoon events recorded by LS46.We believe that this negative shift may be a response to local climate change,which is affected by regional temperature and precipitation.On the multidecade timescale,the stalagmite YX108 closely tracks the 65°N solar insolation changes as a whole,indicating the dominant control of solar insolation on the Asian summer monsoon.After removing the solar insolation signal from the YX108record,the?¹⁸O residuals(??¹⁸O)show 28 multidecadal monsoon cycles.The average amplitude of these fluctuations is larger than 0.8‰,with a duration typically ranging from 50 to 80 a?about 64 a on average?,which is very similar to the mid-late Holocene and Last Glacial Asian monsoon variability,found by YX275 and HL98.Further,wavelet analysis displays a significant quasi-periodicity of 60 years throughout the studied period,providing further evidence for assessing whether the 60-year quasi-periodic variability of the Asian monsoon found in the Holocene exists in older periods.Our study thus suggests that this quasi-periodic variability not only occurred during the modern period but also existed in the Last Interglacial,and their influence may even be an intrinsic characteristic of the Asian monsoon system during glacial-interglacial cycles.We manifested that the interactions between solar activity and the Atlantic Multidecadal Oscillation may be the main reason for the 60-year quasi-period of the Asian monsoon.