A Study On The Early Holocene Monsoon Instability And Climatic Optimization Of The Stalagmite Records In China

The Holocene is an important period of human civilization and social development.The dry and wet changes of climate play an important role in the process of human society reproduction.China has a vast territory and large regional differences.China is effacted by monsoon climate.The difference of climate and environment effacts the distribution of population and the development of society.The optimum period of climate affects the rise and fall of the human civilization.Therefore,understanding Holocene climate change through a good geological carrier plays an important role in studying the evolution of human civilization and predicting future climate change.However,the evolution of the East Asian monsoon is still in a blurred state during the Holocene.Due to the influence of regional differences,dating errors,resolution and proxy indicators,the Paleoclimatic Records of Holocene East Asian monsoon variations from a single research site are inaccurate,incomplete and even contradictory.So far,the Paleoclimatic Significance of stalagmite?¹⁸O and its evolution of Holocene East Asian monsoon are still unclear.This paper compares and analyses the oxygen isotope records of 4 stalagmites from Chongqing and 12 Holocene oxygen isotope records from other caves in the monsoon region of China.It is difficult to use the stalagmite record of a cave to represent the climate change in the eastern monsoon region of China.Because of the discovery of stalagmite records in different caves,there are great differences in the occurrence,negative time and duration of the Holocene stalagmite records.Therefore,we have integrated 16 Holocene stalagmite oxygen isotope records from 14caves in China monsoon area by data synthesis method,trying to explore the climatic significance of stalagmite?¹⁸O in China monsoon area and the evolution of the Holocene east Asian monsoon.Our preliminary results are as follows:?1?The results show that the synthesized Holocene stalagmite?¹⁸O_syn record is basically consistent with other monsoon records in China,which supports that the?¹⁸O record of stalagmite is a good indicator of the intensity of summer monsoon.?2?The stalagmite?¹⁸O_syn record show that at the beginning of the early Holocene,the monsoon strengthened rapidly,and the oscillation of the early Holocene monsoon was relatively large.It underwent three monsoon intensification events,but the duration was not long,which were interrupted by the subsequent weak monsoon events.The monsoon is also strong and stable in the8.0-6.0 kyr BP period.The strongest monsoon period occurs in the 8.0-7.0 kyr BP period of the Middle Holocene.Therefore,the stalagmite records show that the Middle Holocene East Asian monsoon in eastern China is relatively strong,which corresponds to the classical view of a mid-Holocene Optimum in China.?3?Previous studies have fiercely debated the existence of strong or weak early Holocene monsoon in China.However,the study shows that the early Holocene monsoon is unstable and oscillatory,and there are a series of abrupt monsoon events on a centennial-millennial scale.Therefore,in terms of the intensity,duration and stability of the monsoon,the early Holocene is not the strongest period of the Holocene monsoon and the most suitable climate period in China.?4?The stalagmite records show that there are episodes of abrupt strengthening/weakening of the EASM in the early Holocene,which may leave different information in different geological carriers,resulting in deviations in people's understanding of Holocene climate change in China.This may be the main reason for the controversy over Holocene climate change in China.In addition,different geological carriers have certain advantages and disadvantages in recording climate information.Therefore,in order to have a more comprehensive understanding of the Holocene Asian monsoon changes,it requires further investigation.?5?This study supports that climate change in the Asian monsoon region has a certain remote correlation with the North Atlantic.In the Northern Hemisphere,westerly jet may be the link between the East Asian monsoon region and climate change in high latitudes.The response mechanism of China monsoon to PBO and 9.4 kyr BP event and 8.2 kyr BP event in Early Holocene is related to melting freshwater pulses.In the Middle-Late Holocene,the relationship between East Asian monsoon changes and ice sheet changes is not significant.The weakening of solar activity and long-term anthropogenic or 100-year natural variability may be the main driving factors.