Research On Environmental Changes In Northern Lop Nur Based On Cations In Deciduous Layers Of Tamarix Cones

Lop Nur is located on the east side of the Tarim Basin in Xinjiang and is a world-famous arid center.The Lop Nur region is famous for its special geographical location and fragile and sensitive natural environment.The ongoing environmental changes in Lop Nur region have gradually attracted the attention of the scientific community and have become an ideal place and hotspot for paleoclimate research.However,further studies on high-resolution environmental changes in this region are needed.The research shows that the sedimentary veins of Tamarix cones have the advantages of rich climate and environmental information and date sequence with high resolution,and are also suitable for the reconstruction of high-resolution climate and environmental change sequence in the study area.Therefore,this paper takes two Tamarix cones in the lower reaches of Kongque River and Hongliujing in the northern Lop Nur area as the research objects,and the profile depths are 1.76m and 2.46m respectively.The 68 of age data were measured by ¹⁴C,²¹⁰Pb and ¹³⁷Cs methods to determine the age of the sedimentary veins in Lop Nor region,and the tree-ring correction model was used to verify the accuracy of the dating.And the obtained 192 of cation content data through experiments,combined with the 1960-2019 temperature,precipitation and wind speed data of Kongquehe Meteorological Station and Luozhong Meteorological Station,with K⁺,Ca²⁺,Na⁺,Mg²⁺contents as the main indicators,the Correlation analysis method,Stepwise regression method,orthogonal empirical function EOF,FFT Fourier fast algorithm,linear fitting and other methods are used to establish the high-resolution cationic age sequence of the sedimentary veins of Tamarix cones;the Stepwise regression model is used to reconstruct the temperature,precipitation and wind speed sequences of the past about 100 years using the cationic information of the fallen leaves in Tamarix cone sedimentary veins.Combined with the records of meteorological stations and the records of K⁺,Ca²⁺,Na⁺,Mg²⁺contents in the fallen leaves of the Tamarix cone sedimentary veins,a comprehensive analysis of the variation trends of temperature,precipitation and wind speed in the northern Lop Nur region is carried out,which is a quantitative reconstruction of the changes in temperature,precipitation and wind speed in the Lop Nur region in the past hundred of years.Provide preparation and support for further understanding of regional climate system evolution and mechanisms.The results of the study are as follows:(1)based on the comprehensive comparison of the ¹⁴C,²¹⁰Pb and ¹³⁷Cs dating methods,the concluded average deposition rates of the profiles of two sampling sites1.01 cm/a at Hongliujing(20HLJB)sampling site,and 1.03 cm/a in Kongque River sampling site.The age sequence is from 1784 to 2019 at 20HLJB sampling site and is from 1832 to 2019 at 20KQHA sampling site.(2)The contents of K⁺,Ca²⁺,Na⁺,and Mg²⁺in the litter of Tamarix cones are different.Tamarix has the best absorption and utilization rate of Na⁺,Ca²⁺,Mg²⁺,and the absorption utilization rate of K⁺is relatively poor.At the 20KQHA sampling site,the loading of Ca²⁺content in EOF1 is higher,Na⁺content is higher in EOF2,Mg²⁺content is higher in EOF3,and K⁺content is higher in EOF4.At the 20HLJB sampling site,the loading of Ca²⁺content in EOF1 is higher,Na⁺content is higher in EOF2,Mg²⁺content is higher in EOF3,and K⁺content is higher in EOF4.(3)The correlations between the contents of K⁺,Ca²⁺,Na⁺,Mg²⁺in the litter of Tamarix cones and the climate indicators are all ideal,and they can be used as reference indicators for temperature,precipitation and wind speed to reconstruct the annual average temperature,average annual precipitation,and average annual wind speed.The85-year and 107-year climatic and environmental changes in the region,where the20HLJB sampling site is located in the Lop Nur region,reflect the significant increase in temperature and precipitation over the past 59 years,and the significant decrease in wind speed.(4)The Reconstructed temperature sequence using the Ca²⁺content of the20KQHA sampling site shows that the climate change in northern Lop Nur region can be roughly divided into 3 cold periods and 3 warm periods,the period of 1895-1924,1936-1962 and 1974-2019 are cool periods,as well as 1813-1895,1924-1936 and1962-1974 are warm periods.The cold and warm changes of the temperature sequences reconstructed by Na⁺can be roughly divided into 3 cold periods and two warm periods.The reconstructed temperature sequence using K⁺in Lop Nur region can be roughly divided into 2 cold periods and 1 warm period.The reconstructed precipitation sequence using Na⁺can be roughly divided into 3 dry periods and 2 wet periods,the wet periods are in 1826-1879 and 1962-1994,and the wet periods are in 1813-1826,1879-1962 and 1994-2019.The dry and wet changes of the precipitation sequence reconstructed by K⁺can be roughly divided into 3 dry periods and 2 wet periods,the1827-1842 and 1877-1978 are wet periods,the 1813-1827,1842-1877 and 1978-2019are dry periods.At 20HLJB sampling site the temperature sequence reconstructed used by Na⁺in northern Lop Nur region can be roughly divided into 2 cold periods and 2warm periods.The periods of 1900-1926 and 1999-2019 are cold periods,and the periods of 1832-1900 and 1926-1999 are warm periods.(5)Using the Fourier FFT fast algorithm has obtained the reconstructed period of temperature and precipitation in northern Lop Nur region.The oscillation period corresponding to the peak spectrum of the reconstructed temperature sequence based on Na⁺,K⁺,and Ca²⁺content at 20KQHA sampling site is 11a,and that reconstructed by the Na⁺content at 20HLJB sampling site is 12a.The oscillation period corresponding to the peak spectrum of the precipitation sequence reconstructed by Na⁺and K⁺content at 20KQHA sampling point is 1a,while corresponding oscillation period value of Mg²⁺content,the reconstructed peak spectrum of the temperature sequence at the 20HLJB sampling site is abnormal.There is a Corresponding relationship between flooding years in Tarim River and changes in cation content at 2 sampling sites.In a few years,the cation content peaks at two sampling sites have a hysteresis phenomenon,and the decrease of cation content can be clearly found in the next year.With the increase of the Lop Nur water area,the groundwater cation concentration became lower.In addition,the cations of Tamarix cones in Lop Nur region can record El Ni(?)o events.It can be found that the Na⁺content before the potash mine built is larger than that after the potash mine built,and it is found that the precipitation before the salt field is less than that after the salt field,which reflects the impact of human activities on the natural environment.