Response Of Tamarix Cone Pollen Assemblage Of To Regional Environment In Northern Lop Nor Region In Recent 200 Years

Lop Nor region is located in the inland arid area of northwest China,with flat and open terrain,wide spread of Yardang landform,desert landform and Salt crust landform,arid climate.It is a typical temperate continental climate,with high temperature,little precipitation,vigorous evaporation,large temperature difference between day and night,and fragile ecological environment.The environmental change in Lop Nor region,a typical representative of arid zone,has important reference value for the study of regional ecological environment and even global climate change.Based on ²¹⁰Pb,¹³⁷Cs and ¹⁴C dating,98 pollen samples from two sampling sites in Hongliujing and Kongquehe in northern Lop Nor were studied by using pollen analysis and principal component analysis to reveal the paleo environmental changes in northern Lop Nor in the past 200 years.The climate and environment changes in the study area in the past 200 years and the response to the end of the Little Ice Age and the recent global warming period are discussed preliminarily,and the main mechanisms affecting the climate change in this area are analyzed.The following conclusions are drawn:（1）In the past 200 years,the pollen assemblages in northern Lop Nor were mainly herbaceous pollen of Artemisia and Chenopodium,and shrub pollen of ephedra and Tamarix.Tree pollen were less,and their content was less than 5%,which was considered as foreign pollen.The vegetation growth in this area was greatly affected by the change of humidity,but not significantly affected by the change of temperature.Meanwhile,the change of pollen concentration was significant,indicating that the next order of dry and wet fluctuation was frequent in the drought background in the study area in the past 200 years.（2）Because the sampling site of Hongliujing is located in a dry lake basin and the soil salt is relatively high,the pollen assemblage of drought-tolerant plants such as Artemisia,Chenopodium and ephedra is not significantly changed.However,compared with the sampling site of Kongquehe,the pollen content of drought-tolerant plants is higher,indicating that the climate of the sampling site is more arid,and the sampling site is greatly affected by the local climate environment,and the fluctuation of dry and wet is not obvious.During the past 200 years,the climatic changes in this sampling site were mainly divided into two stages:during 1835-1900,the pollen of herbaceous plants mainly belonging to Artemisia and Chenopodium were dominant,followed by those of shrubs such as ephedra.The pollen concentration was low,indicating that the climate was dry.During 1900-2019,herbaceous pollen were still dominant,while shrub pollen content increased.PCA results showed that the score of the first principal component axis was negative,and the pollen concentration increased,indicating a humid climate.（3）The pollen assemblages in the sampling sites of the Kongquehe showed obvious changes,with herbaceous pollen as the main component,and shrub pollen as the second component.The pollen concentrations showed good consistency with PCA results,and the dry and wet fluctuated frequently,which was mainly affected by regional climate and environment,and responded well to environmental changes in Xinjiang and the arid area of Northwest China,reflecting the humid climate at the end of the Little Ice Age and the modern warm period.During the past 200 years,the climatic changes were mainly divided into four stages:during 1815-1829,the pollen of dry plants such as ephedra and Compositae reached the highest profile.PCA results showed that the pollen score was positive,the pollen concentration was low,and the climate was relatively dry.During 1829-1899,the content of Tamarix reached the highest in the section,and the pollen content of dry loving plants decreased.PCA results showed that the score was negative,the pollen concentration increased significantly,and the climate was humid.During 1899-1967,the pollen content of Artemisia and Chenopodium reached the highest,and the shrub pollen content decreased to the lowest.PCA results showed that the score was positive,the pollen concentration decreased,and the climate changed to drought.During 1967-2019,the pollen content of shrub was higher than that of herb pollen.PCA results showed that the score value was negative,the pollen concentration reached the highest in the profile,and the climate was moist overall.（4）The climate change in the sampling site of Hongliujing is greatly affected by the local climate,the climate is generally dry,and the fluctuation of dry and wet is not obvious.In the sampling site of Kongquehe it fluctuates frequently,and the climate response mechanism of the northern Lop Nor region represented by it is the same as that of the arid area in northwest China,which is influenced by the solar radiation,the North Atlantic Oscillation（NAO）,El Nino and other ocean-atmosphere interactions.