Multi-index,High-resolution Stalagmite Records Research During 8000?7000a BP In Chongqing Shuiming Cave,China

Climate warming during the past century is the fact,natural factors and human activities affect the earth's climate.To improve the abilitiy to forecast the changes of climate and environment,carries must take advantage of high-resolution Paleoenvironmental records of past climate change and variability studies to clarify past climate instability mutation rules,boundary conditions,factors and mechanisms.8000?7000a BP high resolution paleoclimate research is scanty,climate during this period as an important condition for agricultural development plays an important role in human life.In addition,there are also some extreme weather events,such as 7200 a,so the high resolution climate record of this period is worth studying.As a carrier of paleoclimate,stalagmite's biggest advantage is high-precision chronology,and abundant proxy indexes.In addition to oxygen isotope records,more and more researchers pay attention to the trace element record.This paper is based on Chongqing Fengdu as the study area,where is sensitive to the Asian monsoon climate.We have reconstructed paleoclimate evolutionary series from 8000 a BP to7000 a BP based on the U/Th age,oxygen isotope,carbon isotope and trace element of stalagmites SMY2,conclusions are drawn as follows:?1?Shuiming cave SMY2 stalagmite ?¹⁸O records show that there is multiple decades to centuries climate fluctuations in 8000?7000a BP: in 8000?7600a BP,stalagmite SMY2 ?¹⁸O reaches a bias of valley value in 7700 a BP,comparation with Henan Magou cave and Guizhou Dongge cave,shows this is a weak monsoon mutation event;in 7600?7300a BP,?¹⁸O and ?¹³C curve show multi-centuries cycle fluctuations,change mode is stable;in 7300?7000a BP,?¹⁸O appeares a weakened monsoon events which lasting about 200 years,by mutation analysis,the mutation index is greater than the sine wave.This dates Suggest that during this time there is a cool monsoon event,namely: 7200 a BP events.?2?The solar radiation energy changes and the Northern Hemisphere high latitude climate change situation affect the variation of Asian monsoon.Over a long time scale the present high-resolution Shuiming cave stalagmite SMY2 ?¹⁸O and ?¹³C records reflect the driving mechanism.The positive correlation of the oxygen and carbon isotope indicates that the hydrothermal form in this area may be: warm and humid,cold dry mode and vegetation rapidly response to climate changes.In addition,?¹⁸O record shows a broad similarity to the ?¹⁸O records of Greenland ice—Greenland Ice Sheet Project 2?GISP2?,suggests Asian monsoon changes are closely linked with the high latitude temperature change.On centennial-scale,The coupling effects of the sea-atmosphere interaction have also had a complex effect on the Asian monsoon change.In terms of frequent decadal scale and centennial-scale fluctuations,the centennial-and multidecadal-scale AM variations during the 8000?7000a BP are considerable(?0.2 ‰ to 0.6‰ in ?¹⁸O)but not as large as glacial millennial-scale variability(?1 ‰ to 2‰in ?¹⁸O).The complete ablation of the Scandinavian and Lauren ice sheets prior to the 7500 a BP resulted in a reduction in the suppression of ice melting on the Asian monsoon variability,while the effect of the tropical Pacific Ocean increased.The atmosphere-sea interaction magnifies the sun's activity regulation of the monsoon system,resulting in stalagmites ?¹⁸O decadal scale fluctuations frequently during 8000?7000a BP.As well as the Shuiming cave SMY2 ?¹⁸O spectrum analysis revealed,that not only did both changes in solar radiation and climatic changes at high northern latitude affect the Asian summer monsoon variations during the Holocene,but also ENSO and the internal interaction of climate sub-systems had significant impacts on East Asian summer monsoon changes.?3?The Mg/Ca,Sr/Ca,Mg/Sr,Ba/Ca and U/Ca ratios in the stalagmite SMY2 are consistent with the changes of ?¹⁸O and ?¹³C,and the wet and dry climate change of 8000?7000a BP is well documented.Mainly for three main periods,that is,the variation of trace elements from 8000 a BP to 7300 a BP is stable,and the fluctuation period is from 7300 a BP to 7000 a.BP;7600a BP?7300a BP trace element ratio Mg/Sr,Ba/Ca and U/Ca curves and ?¹⁸O sequence recorded three hundred-century scale fluctuations,while the fluctuation amplitude of Mg/Ca and Sr/ Ca curves is smaller than that of Mg/Sr,Ba/Ca and U/Ca.Mg/Ca and Mg/Sr are controlled by precipitation.Mg/Ca had a higher value when weak monsoon events occurred.Sr/Ca,Ba/Ca and U/Ca are controlled not only by precipitation,but also by the cave overlying soil,vegetation and atmospheric dust activities.