Physicochemical characteristics and sources of atmospheric dust deposition in snow packs on the glaciers of western Qilian Mountains, China

Wind-blown dust derived from the arid and semi-arid regions is an important atmospheric component affecting the Earth's radiation budget. Dust storms are prevailing in central Asia. Deposition of atmospheric dust in snow was measured on Glacier No. 12 (5040 m a.s.l.) in the Laohugou Basin and Shiyi Glacier (4510m a.s.l.) in the Yeniugou Basin, of western Qilian Mountains, China, mainly focusing on dust concentration and size distribution, chemistry, SEM-EDX analysis and Nd-Sr isotopic composition. An analysis of spatial distribution of dust concentration and size distribution in the snow cover at two sites suggests that deposition of dust in western Qilian Mountains is different between sites as the environment changes from west to east. Mean mass concentration of dust with 0.57 < d <40 mu m in the snow is 3461 mu g kg(-1) on Glacier No. 12 and 2876 mg kg(-1) on Shiyi Glacier, respectively. Annual flux of dust deposition to western Qilian Mountains has a range of 143.8-207.6 mu g cm(-2) y(-1) for particles with 0.57 < d < 40 mu m. Dust layers in the snowpit contain Ca- and Na-rich materials typically found in Asian dust particles. Number-size distribution indicated that most of the dust diameter is <2.0 mu m, implying the significant influences of finer particles to alpine glacier regions of central Asia. Volume size distributions of dust particles showed single-modal structures having volume median diameters from 3 to 22 mu m, which is comparable to the results of dust deposition on glaciers of the adjacent Tianshan Mountains in western China. SEM-EDX analysis suggested that dust particles were mainly composed of mineral particles, besides some fly ash particles and soot. EDX shows that mineral particles contain Si-, Al-, Ca-, K-, and Fe-rich materials, such as quartz, albite, aluminate, etc. The Nd-Sr isotopic composition of insoluble particles in two glaciers showed that Badain Jaran Desert and Qaidam Basin were the most possible source regions of dust in the western Qilian Mountains. Physicochemical constituents of dust indicated that the snowpack was influenced by both local atmospheric environment, e. g. local dust, and anthropogenic activities in central Asia.