| The vertical water migration in arid area plays an important role in the development and maintenance of lakes.However,the study of environmental evolution has focused on regional precipitation,and the study on the environmental evolution of groundwater recharge lake is lacking.The Badain Jaran Desert is located in the arid area of northwest China.It is an ideal place for the environment evolution of groundwater recharge lake in the hinterland of Badain Jaran Desert.In this study,the environmental evolution of the Holocene in millennium and century scale in the Badain Jaran desert since the Holocene was reconstructed by analyzing the environmental factors such as the particle size,total organic carbon,pollen and n-alkanes in the hinterland of the desert.And through the comparison of the main proxies,we probed into the sensitivity and the applicability of the environment proxy,such as grain size,total organic carbon,pollen and n-alkanes.According to the Badain Jaran Desert sedimentation records,the regional environmental change can be divided into six stages.Between 11 ka and 10.2 ka,it is relatively wet under evidence of the lower trees,shrubs pollen content,highest Gramineae pollen content,lowest drought resistant plants pollen content,finer grain size,and higher A/C.Between 10.2 ka and 7.2 ka,it is dominated by typical grassland landscape,and the pollen content of Gramineae plants is reduced,and Artemisia and Chenopodiaceae are dominant.The sedimentary facies change from the marsh phase to the lake facies,and the environment is more humid.Between 7.2 ka and 5.6 ka,it is dominated by typical steppe,Artemisia and Chenopodiaceae are still dominant pollen.A/C is larger,the highest content of drought resistant plant pollen is the lowest,and the first principal component of humid is the smallest.This shows that the environment is more humid throughout the period,reaching the most humid period since Holocene.But the content of Artemisia tends to reduce,indicating that although the environment is moist,but the overall trend has begun to turn dry.5.6-3.6 ka Artemisia and Chenopodiaceae pollen content decreased,ephedra pollen content increased from the typical grassland landscape into desert grassland landscape.Pollen concentration is low.Artemisia decreased,the pollen of xerophytic plants increased,the first main ingredient score on behalf of wet and dry,Pwax larger,increased terrestrial plants,aquatic plants decreased,indicating that the environment turned dry.In 3.6-0.8 ka,the grain size was coarser and aeolian sand was transported into the lake.Pinus and Ephedra covers higher pollen content,besides,Artemisia and Chenopodiaceae covers relatively lower pollen content.The lake is further shrinking and the lake basin showed mainly desert steppe landscape with more eremophyte.More pollen of drought resistant plants and less Artemisia,larger Pwax,indicate more emergent aquatic plant and more drier condition.As to the trend of environment change between 3.6 ka and 0.8 ka,it is gradually wetter with the decreasing grain size and increasing drought resistant plants pollen.In summary,the Badain Jaran Desert groundwater recharge lakes manifest wetter during the early and middle Holocene,and drier in late Holocene.By analyzing the peak of the short term(non-millennial scale)of the main proxy of AR profile,ten environmental events were identified including the wet events of 10.3 ka,7.4 ka,6.3 ka,4.2 ka,and 0.4 ka and drought events of 9.4 ka,8.2 ka,5.4 ka,2.8 ka and 1.4 ka.And these events,except for events of 6.3 ka and 5.4 ka,are consistent with the North Atlantic cold event as a response to global climate change.Through the analysis of the geological archives since 0.8ka,we found that it is wet and cold in 1400 ~ 1850,Badain Jaran desert cold and humid,controlled by the small ice age.There were three obvious cold and wet events in the Little Ice Age,which were 1450-1510,1610-1680 and 1750-1850,respectively.The three cold and wet events were dominated by the intensity of solar activity volcanic activity. |
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