Vegetation And Climate Changes On The North Slope Of The Western Tianshan Mountains Recorded By Spore Pollen Over A Thousand Years

The past millennium has been an important period with the most close relationship with mankind.Among them,the Medieval Warm Period（MWP）and the Little Ice Age（LIA）have attracted the attention of many scholars at home and abroad.However,there are still many disputes about the starting and ending time of these two climatic stages,and the combination of water and heat.This paper selects the Zhaosu section on the northern slope of the West Tianshan Mountains as the research object,establishes a chronological framework through AMS¹⁴C total organic matter dating,and then uses indicators such as spore and pollen to analyze and discuss the climate change in the past millennium,and reconstructs the history of vegetation change in the past millennium,and then combines the changes of A/C value and AP/NAP value as well as PCA principal component axis scores to explore the laws and driving mechanisms of climate change in the Middle Ages and the Little Ice Age.The results are as follows:1.As the depth increases,the lithology changes from brown peat to black peat.2.The variation of the content of various species of spores and pollen and the fluctuation of relevant indicators reveal that the climate change stage of the Zhaosu section on the northern slope of the West Tianshan Mountains over the past thousand years is:（1）1046-1146AD:herbaceous plants with Artemisia and Chenopodiaceae as the dominant species are mainly accompanied by trees and shrubs with Picea as the dominant species.The content of herbaceous plants is more than that of trees and shrubs.The climate is dry and the sedimentary environment is mainly black peat.（2）Medieval Warm Period（1146-1288AD）:This period belongs to the Medieval warm period.At this stage,the percentage of trees and shrubs increased,the content of herbaceous pollen began to decrease,and the content of Picea continued to increase.Picea is the dominant type of vegetation.Lithology is gradually transiting from black peat to brown peat.The climate as a whole is warm and wet,but there are many secondary fluctuations,showing a climate pattern of"two wet and one dry".（3）1288-1476AD:This stage is the transitional period between the Medieval Warm Period and the Little Ice Age.The content of trees and shrubs increases,the types of terrestrial herbs continue to decrease,and the aquatic（wet）herbs reach the peak of the profile.The climate as a whole develops in the direction of cold and wet,during which the humidity changes significantly,showing a"warm wet-cold wet-cold wet"pattern.（4）The Little Ice Age（1476-1606AD）:This stage belongs to the small ice age,and the content of trees and shrubs reaches the peak,among which the content of Picea is also the maximum value of the profile,the content of terrestrial herbs decreases to the valley value of the profile,Artemisia and Chenopodiaceae reach the minimum value of the profile at the same time,but the content of aquatic（hygrophytic）herbs decreases.Picea is the main species of vegetation.The precipitation is more,the humidity is higher,and the climate is mainly cold and wet.3.The climate change on the north slope of the West Tianshan Mountain has fluctuated frequently over the past millennium,with obvious characteristics of climate change.The warm period in the Medieval Warm Period showed warm and wet characteristics,while the climate in the Little Ice Age was cold and wet."Warm and wet-cold and wet"was the main feature of climate change in the past millennium.4.The temperature change in the study area is consistent with the fluctuation of solar radiation,and solar radiation directly affects the temperature change in the period of climate characteristics in the study area.The variation of thermohaline circulation interferes with the temperature fluctuation in the study area to some extent.In addition,the concentration changes of greenhouse gases such as CO₂ and CH₄ have an important impact on the study area,indicating that human activities have a certain impact on climate change.5.The change of humidity in the study area is perfectly consistent with the change of North Atlantic Oscillation,indicating that the main driving factor of humidity change in the study area in the past millennium is North Atlantic Oscillation.