Study On Geochemical Characteristics Of Glacial Deposits From Ny-alesund,Arctic

Glacial deposits are main sources of global dusts,which link to global climate,atmospheric aerosol,the oceanic elemental cycles and productivity of the ocean.There has been a focus on the studies of contemporary dust sources(especially the desert and loess)at middle&low latitudes,but these have been lack of research on modern high-latitude dust sources,which come primarily from glacial sources.The research in this paper provides basic data for the study of glacier and environment in Ny-Alesund,Arctic and raises our understanding of the physical and chemical characteristics of glacial deposits from the glacial dust source and their responses to environmental changes.Based on the field investigation,experimental analysis and data processing,here,we investigate the grain size,magnetic susceptibility,chemical elements?isotopic composition and mineralogy of the glacial deposits to understand the occurrence characteristics of glacial deposits,and the influence of glaciation,erosion and chemical weathering to physical and chemical property of them in modern periglacial environment,which in Ny-Alesund,Arctic.The main results and conclusion are as follow:(1)The average of grain size of glacial deposits in Ny-Alesund is falls in 9.5 to 194.4?m,with an average of 69.6?m.Sand(46.47%)and silt(48.86%)account for a large proportion and clay(4.67%)is the least.Almost all the moraines have bimodal or multimodal spectrum peaks of grain size and they usually appear at 10?30?m(finer part)and 100?200?m(coarse part).1mm is the border of grain size between crushing particle and grinding particle,which indicates the glaciation is relatively weak in Ny-Alesund,Arctic.The fine component(?63?m)of moraine was lost distinctly because of erosion.The average of grain size of fluvioglacial deposits is 23.7?m,Almost all the fluvioglacial deposits have unimodal spectrum peaks of grain size and it represents the finer parts of the moraine.(2)The magnetic susceptibilitis of moraine and fluvioglacial deposits are similar with local bedrock,with the average of 9.7×10-8m3Kg-1 and 8.5×10-8m3Kg-1 respectively.We suggest that because of weak pedogenesis in periglacial environment,the magnetic susceptibilitis of them are mainly depending on parent material and have an effect by erosion and size sorting.(3)The values of chemical index of alteration(CIA)mainly fall in 55 to 70.We suggest that the CIA values can generally tell the difference of weathering intensity between of LIA moraines and tundra soils in periglacial environment.For LIA moraines that were deposited with relatively short time,the CIA values could mainly be changed by the grain size sorting and corresponding changes of different mineral types and contents in deposits transportation.The average chemical compositions of moraines are very similar pattern with Luochuan loess and Clark values of UCC(Upper Continental Crust).The moraines'values plotted on a trend between UCC and Loess in triangle chart of CIA(Chemical Index of Alteration),thus,provides an implication that the loess dust could come from moraines which are the glaciogenic dust sources.(4)It is obvious that the dissolution of carbonates in the glacial deposits in periglacial environment,especially the ?2?m part.Biological weathering which comed with the vegetation succession in tundra may be the main force about the carbonate leaching.(5)The geochemical characteristics of moraines and fluvioglacial deposits are similar,Carbonates were identified in almost entire profile of fluvioglacial deposits,which indicated the material of fluvioglacial deposits may came directly from the glacier terminus by outwash and have not been affected by hypergenesis.The clay minerals of glacial deposits is detrital origin.Among the component of clay minerals,illite(63%)occupies first place,kaolinite(19%)comes second and chlorite(17%)is the least.The clay with high Sr isotope ratio may be the fingerprint characteristic of glacigenic dust that emissioned from Ny-Alesund or Svalbard.The average content of gothite(0.34%)and hematite(0.2%)in the profile of fluvioglacial deposits are mainly depending on parent material but not pedogenesis.(6)In our study,the changes of element ratios in fluvioglacial deposits indicate the changes of depositsary environment.Dust particles,which were produced in periglacial environment,had their stable geochemistry characteristics which depending on their parent material but not the climate.The dissolution of carbonate minerals is the main manifestation of the weathering of glacial deposits in periglacial environment...