Research On Multi-Proxies,High-Resolution Stalagmite Records During 116~69ka BP From Yangzi Cave,Chongqing,China

Many research results of geologic records showed that,the most typical characteristics in the quaternary are the existence of periodic climate glacial-interglacial cycles.Climate change in the LGP is a series of centuries-millennial scale climate fluctuations,the Dansgaard-Oeschger?D/O cycles?and Heinrich?H?events from ice-cok and other proxy records.The amount of global ice is just beginning to increase,and the global CO₂ concentration is relatively high;the earth orbit eccentricity value is large,and the solar radiation season changes greatly during MIS5.Studying the climate change in the Asian monsoon region during this period helps to fully understand the evolutionary process and driving mechanism of the Asian summer monsoon during this period and its role in the global climate system.This paper is based on Fengdu county as the study area,where is affected by the monsoon primarily.We use the 25 ²³⁰Th dating data and 803 stable oxygen and carbon isotope data of Stalagmite from Yangzi Cave in Fengdu area to establish stalagmite oxygen and carbon isotope time series of high resolution during 116.5⁶8.9ka BP.Combined with the 493-series trace element ratio data series,this paper comprehensively analyzes the characteristics of the external environment in Chongqing during this period.By comparing the 65°N solar radiation curve records,other cave stalagmite records in the Asian monsoon region,non-monsoon regions,Arctic ice core data records,IRD records and Brazil BT2 stalagmite and using multi-period analysis tools,this paper further studys on the changes in the internal characteristics and driving mechanisms of the millennium-scale monsoon climate mutation events in the Asian monsoon region and the special events of 93.1⁹1.5ka BP in the YYZ1 stalagmite as well as explores the coupling and driving mechanism between the high and low latitudes,the northern and southern hemispheres of the climate system.The results as follows:?1?The curve of?¹⁸O from Stalagmites YYZ1 has two peaks and three valleys.There are 5 periods in this curve,which are MIS5d,MIS5c,MIS5b,MIS5a and MIS4.By comparing with the NGRIP and other records?Sambao,Sanxing,etc.?in Asian monsoon region,the results show that?¹⁸O stalagmite recorded six millennial scale events occurring in these stages?GIS25-20?.By comprehensively analyzing the changes of?¹⁸O of YYZ1 stalagmite,it shows that the intensity of Asian summer monsoon gradually strengthens.The?¹⁸O of YYZ1 stalagmite and the 65°N solar radiation curve are basically the same means that the change of summer monsoon intensity is controlled by the external Astronomical precession parameter.It was found that the YYZ1stalagmites can record climate change information in the North Atlantic,and also have a clear?see-saw?effect in the Southern Hemisphere.It explains the closeness of climate links between high-low latitudes and south-north hemispheres.?2?The?¹³C of the YYZ1 stalagmite was negative in the strong summer monsoon?MIS5c,MIS5a?and positive in the weakening period?MIS5d,MIS5b,MIS4?.It reflects the types,density and dry-wet conditions of vegetation outside the cave.However,the differences in mean values at each cold and warm stage is not significant.Mainly in the MIS5c,MIS5a warm period and D/O events it does not appear significant negative"peak"that is similar to?¹⁸O.It was judged that the addition of limestone and the external environment over-wet mode caused the neutralization effect of?¹³C to be positive.The ratios of Mg/Ca,Sr/Ca,and Ba/Ca in YYZ1 stalagmites increased during MIS5d,MIS5b,and MIS4,whereas the levels of MIS5c and MIS5a decreased.It is mainly controlled by the length of karst water migration time,the change of path,and the strength of PCP,reflecting the external dry and wet conditions in Yangzi cave at this time.It confirms that the monsoon enhancement period was indicated by the stalagmite?¹⁸O,and the precipitation in Yangzi cave was large.?3?There is a"V"shaped rapid fluctuation event of the?¹⁸O??¹³C and trace element ratio during the 93.1⁹1.5ka BP,similar to the caves of Kesang in China and Tonnel Naya in Uzbekistan.It is believed that when the Asian summer monsoon get weak and local evaporation increases,the local water vapor with a higher?¹⁸O value is the main source of precipitation,making the?¹⁸O value of the stalagmite extremely high.However,the amount of precipitation is not large.The long-term drought state changes the local vegetation types.At the same time,the role of PCP is strengthened to increase the positive?¹³C value and the ratio of trace elements.In addition,by comparing the records of NGRIP ice core and other stalagmite Asian monsoon area,it has been found that records of D/O25 event in the Asian monsoon region have been significantly smaller than D/O24-20 events.It is believed that this is related to such factors as the initial rising stage of solar insolation and the weak THC in the North Atlantic,lesser transmission of temperature changes in the North Atlantic to Asian summer monsoon.?4?Multi-period analysis shows that the YYZ1 stalagmite has a very pronounced20,000-year precession cycle on the orbital scale,including 23866a cycle of?¹⁸O and10917a cycle of?¹³C.Precession cycle has the highest contribution rate.The millenium-scale cycles?1000a quasi-cycle,2112a,2340a,3876a,4755a?are related to thermohaline circulation or changes in solar radiation caused by ITCZ movements.It reflects northern latitude climate change.The cycle on the centennial scale?534a,408a,250a,207²12a?mainly reflects the influence of solar activity.