Late Holocene Variation Characteristics Of Geochemical Elements And Responses To Regional Environmental Change In Dadi-Nor Lake

Dali-Nor Lake is one of the closed lakes in Inner Mongolia plateau and a typical inland lakes in the cold and arid regions,which is located in the west of Keshiketeng country.Its environmental records of sediment geochemical elements have a high response to regional and global climate and environmental changes due to its special geographical location where is the northern fringe of the East Asian summer monsoon area.A sediment core with a length of 238 cm was sampled in the lake.This sampling position was selected at a typical area with an average water depth in the lake.210Pb,137Cs,AMS14C,and geochemical elements indexes were applied to analyze the sedimentary sequences.About 2400 years sedimentary history was reconstructed according to the record information by the sediment elements.The results obtained were as the followings:(1)The change characteristics and environmental significance of Hg were analyzed based on the sedimentary strata age,the results showed that the contents of Hg recorded in the sediment had obvious characteristics of stage change.According to the chronological order,the sediment characteristics could be obviously divided into three stages.The content of Hg increased sharply in 200 cal.a BP..This mostly could be due to the effects of human activities.The positive correlation between Hg and TOC contents in the past 200 years showed that a large amount of Hg might be adsorbed by the organic matter,which leads to an enrichment tendency on the top layer.This in turn impacted the ecological environment of the lake.(2)The sediment core restored about 2400 years climate change processes of the lake basin.The processes could be divided into 7 warm and humid periods and 7 drought periods.In the warm and humid periods,the weathering and surface runoff were enhanced,the lake water level increased,and the lake water salinity decreased.In the drought periods,the lake water level was lower,the weathering effect was weak,the external input was obviously reduced,and the lake was shrinking.(3)Based on the multivariate statistical analysis method,a variety of geochemical elements were classified and analyzed.The results showed that the results of the three taxonomy were similar.This indicated that the chemical composition of the sediments was mainly affected by basin erosion,early diagenesis,precipitation,and human activities.The basin erosion and early diagenesis played a main role in the chemical composition of the sediments and had a significance to wet and dry climate changes.Endogenous calcium carbonate deposition record could be regarded as a index for climate changes as well.(4)By in the lake sediment core of geochemical elements of climate change and the number of sunspots,the reconstruction of the temperature and precipitation index,ENSO index changes,d18O reveals such as climate change process,this paper compares and analyzes has good response.This approximately agree with the previous research results about the climate fluctuation cycle since 5ka BP in China.The deposition of the core elements successfully recorded the major historical events in the Dali Lake Basin.