Lake Sedimentation Response To Climate Change In The Northwest Zone Over The Past 70 Years

In this paper,Bosten Lake and Wuliangsuhai,typical lakes in the northwest arid and semi-arid region,were selected as the research objects.Through the determination of organic matter content,total organic carbon content(TOC),carbonate content(TCC),carbonate carbon,oxygen isotopes(?¹³C_car,?¹⁸O_car)and particle size parameters in sediment samples,a high-resolution sedimentary chronology was established by combining ²¹⁰Pb,¹³⁷Cs The sequence was used to analyze the change characteristics of various environmental proxies in the lake sediments and reveal the environmental significance of each environmental indicator,thus solving the problem of multiple solutions of a single lake indicator.By exploring the climate and environmental evolution history of the northwest arid and semi-arid region under high resolution for 73years,the response mechanism of the northwest arid and semi-arid region environment to global climate evolution was better revealed,and the following conclusions were initially obtained.1.The vertical changes of organic matter and TOC contents in the sediments of Bosten Lake and Wuliangsuhai are increasing from deep to shallow,and the organic matter and TOC contents of Bosten Lake are slightly higher than those of Wuliangsuhai,and this result is due to the decrease of aquatic plants and plankton due to the anthropogenic pollution in Wuliangsuhai Lake.In addition,the vertical variation characteristics of sediment organic matter and TOC content in both lakes verified that the surface sediments were enriched with plant and animal residues,and with increasing depth,the organic matter content decreased,the accumulation rate slowed down,and the carbon sequestration capacity was subsequently reduced.Combined with the regional temperature data,the rising trend of organic matter and TOC content in the sediments of the two lakes from deep to shallow reflects the gradual increase of temperature in the lake area,so the organic matter and TOC indicators reconstruct the temperature history of the northwest arid and semi-arid region,i.e.the"cold-warm"climate characteristics.2.The carbonate content in the sediment cores of both Bosten Lake and Wuliang suhai reveals that the lake water tends to be saline,and the carbonate content of Wuliang suhai is smaller than that of Bosten Lake.The content of carbonate in the sediment cores of both Bosten Lake and Wuliangsuhai reveals the salinity of the lakes.According to the records of regional temperature and other meteorological data,the change of carbonate content in the sediments of the two lakes from deep to shallow reveals that the climate of the inland northwest is characterized by"cold and wet-warm and dry",so the carbonate content can indicate the temperature of the lake area,i.e.,the temperature rises,evaporation increases,humidity decreases,and carbonate deposition is obvious,so the climate is characterized by Therefore,the climate is characterized as"warm-dry".3.The?¹³C_car and?¹⁸O_car in the sediment cores of Bosten Lake and Wuliangsuhai both show positive correlation,and the correlation of Bosten Lake is better than that of Wuliangsuhai.The two lakes are in the northwest arid and semi-arid region,the lake environment is now relatively occluded,the climate is arid,?¹³C_car and?¹⁸O_car are under the condition of relatively occluded hydrological environment,the strong evaporation in the lake area causes?¹³C_car and?¹⁸O_car to be hosted in the lake water body for too long,and then show good correlation,so?¹³C_car and?¹⁸O_car can reveal The results are fully consistent with the environmental significance indicated by organic matter,TOC and carbonate content.4.The grain size of Bosten Lake is generally coarser than that of Wuliangsuhai,with median grain size(Md)of 44.06?m and 27.00?m,respectively,and the vertical variation of the grain size characteristics of the two lakes has obvious mutation points in1988(29 cm)and 1996(25 cm),showing significant differences between the upper and lower layers.When comparing the time before the abrupt change point,the trend of particle size changes from coarse to fine and from large to small in terms of median particle size.In Bosten Lake,irrigated oasis agriculture and water conservancy projects were developed at the end of 1980s,which brought fine particles into the lake;Wuliangsuhai was due to the development of tourism in the watershed after 1996,and the implementation of greening and dredging of the wetland lake bottom led to fine particles.Combined with the water level and water volume data in the lake area,it is found that the median particle size changes with the change of water volume into the lake,i.e.,the sediment particles become coarser when the water volume into the lake increases,the hydrodynamic force increases,and the ability of transporting medium increases.