Lake Sedimentary Records And Environmental Evolution Of The Holocene In Subenao, Southern Inner Mongolia

Environmental change study in Holocene is one of the hot research issue of the global changes.The Ordos Plateau of South Inner Mongolia is located in the edge of the East Asian monsoon zone and a typical arid and semi-arid eco-fragile areas.It plays an important function in environmental change study in Holocene.However,the current research results of the region is not much,and there are some differences between them.So it needs to put more research work on environmental change study in the different region,avoid from point to area of the institute to bring the one-sided.Taking Subei Nuur as the study area,the paper collects sediment samples from SBN-land SBN-2 profiles by field investigation,gets samples age by means of AMS14C dating and OSL dating,creates the time sequence instauration.Meanwhile,we combining with sediment grain size,magnetic susceptibility,carbonate,reconstructs environmental evolution sequence since Holocene of the study region.Threfore,it is more significant for studies of the processes and mechanism of the environmental change.In this paper,key knowledge and conclusions are as follows:1.Dating results show that the lower limit age of SBN-1 profile is 10920a BP,is a deposition profile that throughout the Holocene,the lower limit age of SBN-2 profile is 3680 a BP which is a deposition profile in later Holocene.Capared the results using method of 14C Radiocarbon Determine Year in the same horizon of SBN-2 profile with Optical Stimulated Luminescence dating,found it is close to each other in the range of allowable error,it shows the dating results that are relatively reliable.2.Based on research work made by pioneers,we discuss the significance of the environmental substitution indexes for grain size,magnetic susceptibility,carbonate etc.in accordance with the practical situation of Subei Nuur basin.As it turned out,there are many semantic differences of indicative significance for some environmental substitution indexes in the different research area.3.According to the time sequence instauration,using the change characteristics of different environmental substitution index to back Subei Nuur basin to Holocene's climate history,the result is divided into eight evolutionary stages:Between 10920 and 9380a BP,the climate is cold and humid,also it is relatively stable.At the same time,lakes maintain high water level;9380?6620a BP,lower temperature,a cool but arid stage and the lake is in the low water level;6620?3380a BP,the mildest climate conditions with a warm and humid in Holocene and with the high water level of lake;3380?3080a BP,the climate is totalily humid,the water level is high but lower than upper stage;3080?2700a BP,a dry and cool stage,lake shrinking;2700?2150a BP,a dry and cool stage totalily,but there is a short time wet period,the lake is shallow but have obvious high and low level fluctuations;2150?1250a BP,a cool-wet stage,and the climate changes relatively frequently,with the water level of a lake are generally low,and the fluctuations are frequent but the range is not too much;Since 1250a BP,the condition is warm-dry and partial wet,but is partial cool-dry in the later,with the water level of a lake increased slightly than the upper stage.4.Set the contrast between the records of two deposition profile and the climate records of Ordos Plateau and surrounding areas by predecessors,the results show that climate environment evolutionary pattern not only has the uniformity,but also has difference.Uniformity reflected in climate evolution model that the conditions are cold-humid,cool-arid,warm-wet and dry-cool in the early,medium and late Holocene in Subei Nuur basin have the similar performance not only in Ordos Plateau region,but also in other regions of the Inner Mongolia numerous research,which explains that the evolution of regional climate environment is influenced by common global climate change.Difference reflected in climate evolution model that the beginning and ending time of climate evolution period and hydrothermal conditions in different period are different,which related with the differences of atmospheric circulation of different regions,using different environmental substitution index,different time resolution in samping and different dating methods and dating errors.5.More index records of two deposition profile in this article show that the hydrothermal conditions between 6.6?3.3 ka BP is the best climate appropriate period,which proved by regional climate's records of Ordos Plateau.And between 6.1?5.5ka BP,a short climate aridity Mutations events appearing,which coincides with the other results that there was climate aridity events around 5.5ka BP.But part of the research achievements think that the climate of Ordos Plateau is war-dry stage in Mid-Holocene,which is not consistent with the research conclusion of this paper.After comprehensive consideration,we tend to support the view that the climate condition in medium Holocene is war-wet.And there are dry climate events,nothing but the beginning and ending time and level of the drought events are different.Therefore,we need further research for the point that the climate of Ordos Plateau is warm-dry in Mid-Holocene.