| Understanding the biogeochemical cycle of trace element(TE)is important because TE is closely linked to ecosystems and human health.A large number of studies in the past indicate that natural sources of TE in the atmosphere mainly include crustal dust,sea salt spray,volcanic eruption and wild forest fire,etc.,while anthropogenic sources mainly include non-ferrous metal mining,smelting and fossil fuel combustion.Since the Industrial Revolution,increased human activities have emitted a large amount of TEs into the atmosphere,which has caused potential threats to ecological environment and public health and safety.Based on the studies of TE in Greenland and Antarctic snow and ice over the past few decades,the results showed that TEs emitted by human activities are transported over large distances at hemispheric or even global scales through atmospheric circulation,which has become a global environmental problem that cannot be ignored.Compared to polar glaciers,given that mountain ice cores in the middle and low latitudes are closer to human activity sources,they are more sensitive to changes of TEs in atmospheric deposition and can well document and reflect anthropogenic emissions in the past on a long-term scale.The Miaoergou Glacier(43°03? N,94°19? E)in eastern Tien Shan is located in an arid and semi-arid region of the middle latitude,where there is significant wet and dry seasons,and is controlled by westerly circulation all year round.The transport pathways of water vapor over eastern Tien Shan include the important human activity regions such as Europe and Central Asia.Therefore,these conditions are favorable basis for the study of glaciochemical record in Miaoergou Glacier.Ice core,with characteristics of high fidelity and less interference from human activities,is a natural and precious archive of climate and environmental changes.It can reconstruct the past climate and environmental changes in high resolution,and has been widely used in the world for the reconstruction of paleoclimate and paleoenvironment.Previous studies on TEs in atmospheric deposition in Tien Shan have a short time span,such as the records of western Tien Shan(1908-1995),central Tien Shan(1992-1998),and eastern Tien Shan(1953-2004),which cannot reflect the impact of anthropogenic emissions from Europe and Central Asia on the atmospheric environment of Tien Shan since the Industrial Revolution.In this study,we reconstructed a high-resolution TE record in atmospheric deposition during 1776-2004,including V,Mn,Co,Ni,Cu,As,Rb,Sr,Mo,Sn,Sb,Ba,Tl,Bi,Th,U,Cr,and Pb via the Miaoergou ice core,eastern Tien Shan.Based on this reliable record,we evaluated the impact of anthropogenic and natural activities on the atmospheric environment in the Miaoergou area for the past 230 years.The major conclusions are as follows:(1)Based on empirical orthogonal function(EOF)analysis of TE,EOF 1 explains ?81.99% of the total variance,indicating that major TEs(V,Mn,Co,Ni,Cu,As,Rb,Ba,Tl,Th,U and Cr)originate from crustal dust.EOF 2 accounts for ?8.34% of the total variance,including Sr,Mo and U,primarily from the evaporite mineral.EOF 3 & 4 explain ?5.91% of the total variance,representing changes of TEs affected by human activities,including As,Sn,Sb,Bi and Pb.According to the analysis of enrichment factor(EF)and excess concentration(Ex)of TE,it was concluded that there were sporadic Ex concentrations of Pb,Sn,Cu,Sb,and Tl before 1950,while EF values and Ex concentrations of Pb,Sn,Cu,Sb,As,Bi,and Tl increased significantly after 1950,indicating that these TEs may be affected by human activities.(2)Using backward trajectories of air masses by Hysplit,the results showed that air masses over the Miaoergou area are mainly from Xinjiang in northwestern China and most countries in Central Asia,followed by Eastern European countries,indicating that anthropogenic emissions in these areas may be responsible for changes of TEs in the Miaoergou area.The analysis of Sr-Nd isotope composition of insoluble dust in the Miaoergou ice core showed that the crustal TEs came from the Taklimakan Desert and the Gobi Desert.The analysis of the Pb isotope composition showed that there was dust contribution from the surrounding deserts,as well as the effects of mining operations in Tien Shan and Altai regions,and fossil fuel combustion in China and Russia.(3)Based on the analysis of the trends of all TEs,the results showed that changes of TEs have obvious seasonal characteristics,with elevated concentrations in winter and spring and low concentrations in summer and autumn.The reasons may be that there is more precipitation in summer and autumn,which has a "leaching" effect on the suspended dust particles in the atmosphere,while there is less precipitation and frequent sandstorm activities in winter and spring.By analyzing EOF 1 series representing changes of crustal TEs,it was found that the high-value periods of TEs include 1830-1850,1865-1880,1915-1925,1987-2004,and low-value periods include 1850-1865,1880-1890,1872-1887,and 1972-1987.These trends are basically similar to the trends of insoluble particles,which is likely to be dominated by sandstorm activities and atmospheric circulation.In addition,the trends of Pb,Sn,Sb,Cu,As,Bi,and Tl increased significantly after 1950,peaked in 1970s-1980 s,and then began to decline,and eventually rose again at the end of the 20 th century.These trends of TEs likely reflect changes of anthropogenic emission activities in the potential source areas(Central Asia,Europe).(4)By comparing EOF1 series with the sandstorm frequency recorded by meteorological stations around the Miaoergou area during 1954-2004,the results showed that dust emitted from Taklimakan Desert is an important factor affecting atmospheric deposition in the Miaoergou ice core.Secondly,volcanic eruption contributed to enrichments of some TEs(Pb,As),while sea salt spray and wild forest fire contributed less to enrichments of TEs.In addition,correlation analysises between EOF 1 and precipitation,sc PDSI,soil humidity,and near-surface wind speed in the potential source area indicate these climatic factors are also the driving factors that affect changes of TEs in the Miaoergou area.(5)By comparing the widely studied Pb concentrations in ice core,the results showed that Pb enrichments were widespread after 1850.However,the enrichments of Pb,Sn,Cu,Sb,and Tl before 1950 may originate from coal combustion and non-ferrous metal smelting activities after the European Industrial Revolution.After 1950,the Ex concentrations and EF values of Pb,Sn,Cu,Sb,As,Bi,and Tl increased significantly due to non-ferrous metal smelting\production and fossil fuel consumption\production activities in the Central Asian Commonwealth of Independent States(CIS)countries.In addition,agricultural activities in Central Asia are likewise the main factors for Pb and Cu enrichments.This result confirms that changes of TEs from Miaoergou ice core can reflect changes of anthropogenic emissions from potential source areas in the past. |
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