Decadal-centennial Scale Climate Variations And Mechanism Of Asian Summer Monsoon Derived From The High Resolution Stalagmite Record In Xiaosanyan Cave,Chongqing

Modern observations show a large spatial difference in precipitation in the monsoon region of our country on the interdecadal scale,suggestting a phenomenon of inconsistency between the South-North/South-Middle and Lower Yangtze River-North.The comparison of reconstruction records shows that the precipitation in southern China and northern China shows a reverse phase change relationship on the100-year scale.However,in a typical climatic period?such as the Little Ice Age?,it shows a more consistent change characteristic on the interannual-decadal scale.The characteristics of the spatial difference and consistency of precipitation at different time scales in the north and south of our country require further res earch on the proxy index records with high resolution and high dating accuracy.On the other hand,on the interannual-decadal scale,instrumental records,results of proxy index reconstruction,and results of numerical simulation studies all show strong connections.However,the high-resolution and continuous precipitation records of the central and eastern monsoon core areas in China are still lacking,which limits the understanding of the precipitation characteristics and driving mechanism of the monsoon climate core area.Therefore,it is necessary to further enrich the high-resolution,continuous sedimentation and accurate dating precipitation records in the region.The Xiaosanyan Cave?29°43?N,108°23?E?is located about 150 kilometers northeast of Chongqing.This area belongs to the humid monsoon climate zone in the mid-subtropics.The average temperature for many years is about 17.5?,with the highest temperature about 27.3?in summer and the lowest temperature about 7?in winter.The average annual precipitation is about 1200 mm,and the summer precipitation is about 710 mm,accounting for 60%of the annual precipitation.Based on the 69 ²³⁰Th data and 3520 groups of oxygen and carbon isotopes for four stalagmites?No:XSY,XSY13,XSY16 and XSY17?in the cave,the summer monsoon precipitation records with an average time resolution better than 1 year since3000 years was reconstructed.With good reproducibility characteristics,the four stalagmites recorded a coincidence in the past 300 years.Despite the sedimentary discontinuity of about 700 years,XSY13 and XSY16 stalagmites recorded good reproducibility in the past 3000 years.At the same time,it has good reproducibility with other stalagmite records in the monsoon area,indicating that the stalagmite deposits in Xiaosanyan Cave have reached equilibrium fractionation and can be used for paleoclimate research.The cave monitoring results show that the?¹⁸O of the cave drip water is consistent with the regional atmospheric precipitation line,indicating that the stalagmite?¹⁸O of the Xiaosanyan Cave inherits the signal of the atmospheric precipitation?¹⁸O.Further comparison with the precipitation data from instrumental measurements shows a good consistency,indicating that the stalagmite?¹⁸O in Xiaosanyan Cave mainly reflects the change of regional summer precipitation.The stalagmite?¹³C record showed a consistent change characteristic in the recent 300 years,but it has been significantly different since 3000 years.Comparing the stalagmite?¹³C record with the regional instrumental records,the results show that although there is a certain similarity with temperature and precipitation,the correlation is low,indicating that the stalagmite?¹³C influencing factors are complex and may reflect the area affected by the combined temperature and precipitation Changes in soil productivity.The ensemble empirical modal method is used to decompose the stalagmites records of the Xiaosanyan cave,and the results show the characteristics of multi-time scale changes.At the same time,the decomposition results show that there are quasi 2-7 a,11 a,30 a,60 a,110 a,210 a,and 550 a change periods,indicating that ENSO and solar activity are the main influencing factors of precipitation in the monsoon area during the last3000 a.On the millennium-centennial scale,typical climatic events?2.8 ka event,Medieval Warm Period,Little Ice Age and Current Warm Period?were recorded by the stalagmites of Xiaosanyan Cave.These events are consistent with the previous stalagmite research results,indicating that the typical climatic period in the Asian monsoon region has broad consistency characteristics.On the decadal-centennial scale,monsoon precipitation is affected by solar activity and the average state of the tropical ocean.The 2.8 ka event showed significant changes in the two valleys and one peak,which is consistent with the record of solar activity indicators and the record of ENSO activity indicators.Significant interdecadal-centennial oscillations also existed during the Medieval Warm Period and the Little Ice Age,indicating that solar activity affects precipitation changes in the monsoon area through the magnifying effect of air-sea coupling.The normalization results of the high-resolution stalagmite record show that at least 55 interannual-decadal monsoon precipitation increases and 40 monsoon precipitation reductions were recorded since 3000 years.Research on the relationship with ENSO and PDO shows that on the interannual-decadal scale,there is a significant coupling relationship between monsoon precipitation changes and the tropical Pacific sea surface temperature.During El Ni?o,the sea surface temperature of the equatorial eastern Pacific increased,the Walker circulation weakened,resulting in a weaker Hadley circulation and reduced monsoon precipitation.During the past 2000 years,stalagmite records in Asian monsoon region have a wide range of consistency characteristics on the centennial scale,and significant coupled with the northern hemisphere temperature records,indicating that temperature has an important driving effect on the Asian summer monsoon precipitation.On the interdecadal scale,there is a coupling of temperature and monsoon precipitation in some periods.The most significant change is that the summer monsoon precipitation decreases significantly in the context of a significant increase in global temperature in the last 100 years.The trend is opposite to the temperature change,which may be Due to the increase in surface temperature of the tropical ocean caused by human activities,the thermal gradient of land and sea is reduced.Meanwhile,a comparative study using regional wind fields under different temperature backgrounds shows that when the temperature is relatively high,the main monsoon area in China mainly comes from the tropical Indian Ocean;while when it is relatively cold,the monsoon area is mainly derived from the South China Sea,indicating that different The source of water vapor is also an important reason for different changes of stalagmite?¹⁸O under different temperature backgrounds.The stalagmite record of Xiaosanyan Cave has a good correspondence with the instrumental ENSO index,which shows that during the El Ni?o event,Asian monsoon precipitation decreased and the stalagmite?¹⁸O was positive.The stalagmite signal has a good correspondence with the ENSO reconstructed by the tree ring and the sea surface temperature record of the tropical Pacific coral reconstruction,indicating that the stalagmite?¹⁸O in the Asian monsoon area has the potential to reconstruct the history of ENSO activity.According to the stalagmite records,there have been at least four periods of intense ENSO activity in the past 3000 years,namely during the 2.8 ka event,the late Medieval Warm Period,the late Little Ice Age and the Current Warm Period.In the context of global climate change,ENSO activities continue to increase.The precipitation in the Asian monsoon region was significantly affected by the ITCZ.The ITCZ index since 3000 years was reconstructed using the stalagmites records in the middle and lower reaches of the Yangtze River and southern China.The index shows that the ITCZ has shown a significant northward movement/expansion since the last 3000 years.Additionally,ITCZ also has a significant 100-year scale change process.Power spectrum analysis shows a quasi-100-year scale change cycle,indicating that changes in solar activity on the 100-year scale have a significant control effect on ITCZ.This study provides continuous high-resolution records of stalagmites in the Asian monsoon region over the past 3000 years.The comparative study reveals the spatial connection of the Asian monsoon region on the centennial scale of precipitation,confirming a widespread monsoon precipitation at least on the centennial scale.Spectral analysis results and normalization results show significant changes in monsoon precipitation on the annual-decadal scale,which is consistent with ENSO variability,indicating that the tropical Pacific sea surface temperature is the main reason for the short-scale climate variability in the Asian monsoon region.Xiaosanyan records also provide basic data for model simulation to study the characteristics and mechanisms of changes in multiple time scales in the late Holocene.