A 400-Year Vegetation And Climate History Inferred From Dali Lake Pollen Record,Inner Mongolia,China

According to IPCC 5th Assessment Report issued by IPCC in 2014,the mean global temperature has increased continuously,and the tendancy of global warming is still upwards.Based on"Multi-mode Estimates of Global Precipitation Change Pattern",IPCC researchers put forward that humid area will become moister,at the same time,the arid areas will have much more drought.The northeast part of China belongs to the humid area of the pattern.Yet the environment of northeast part of China is much complex due to its diverse and rapidly shifty climatic zones.The crux is that whether the pre-estimated results from AR5 could be exactly appropriate for the diverse climatic zones in northeast part of China.Pollen records in the lake sedimentation are selected as the substitutal index in this study and paper,in order to establish a high-resolution palynological deposition sequence to observe the reflection of global warming in the semi-arid zones.This study analyzed sendimental pollens in Dali Lake of Inner Mongolia,Timing is measured by ²¹⁰Pb and ¹³⁷Cs isotopes,and the age span of sedimental deposition in Dali Lake is 1597-2006AD.The main results of this research are as follows:1.In the sediment of Dali Lake of Inner Mongolia,it is mainly herbal-based with substantial representatives such as Artemisia and Chenopodiaceae,and all tree palynological grains were coming from the outside,which indicates that it is a typical prairie environment during past almost 400 years.2.There are three pollen assemblage zones:the zone I is from 1597 to 1645,it is a relatively cold and moist period,with a trend of growing humidity;palynological zone II is from 1645 to 1893,there was a tendancy of becoming moister in this span,pollen assemblage III(1893-2006AD),it is a period of relative warmth and drought.3.According to the characteristics of vegetation types,researcher reconstructed paleoclimate change processes of nearly 400 years in the past.1597-1645AD,the climate is characterized by relatively cold and humid,1645-1910AD the climate has gone through a“cold and dry-cold and wet”oscillation proccss:(1645-1777AD)climatic characteristics is of relatively cold and dry,(1777-1893AD)climate characterized by relatively cold and wet;1893-1979AD,the climate is characterized by relatively warm and humid;1979-2006AD,the climate is characterized by relatively warm-dry.4.By analyzing the meteorological records nearly 60 years in Lin Xi station closed to the study area,we found that mean temperature has experienced a continouse warming progress and annual precipitation has been a fluctuating reduction trend.5.With the global warming,precipitation of semi-arid will decrease in northeast part of China,which is inconsistent with the results predicted by IPCC.