Seasonal evolution of aerosol stratigraphy in Urumqi glacier No. 1 percolation zone, eastern Tien Shan, China

The processes involved in the evolution of veritical profiles of Mg2+, Ca2+ and microparticle concentrations, as well as their seasonal variation in surface snow, were studied by weekly sampling from September 2003 to September 2004 of a snow pit on Urumqi glacier No. 1, eastern Tien Shan, China. The development of the microparticle and Mg2+ and Ca2+ stratigraphy in the snow pit is closely related to the physical development of the snow-firn pack. The sampling site is located at 4130 m a.s.l. in the percolation zone of the glacier, and in addition to the effects of sublimation and wind erosion, melting plays a crucial role in both the physical and chemical evolution processes. During the winter, soluble aerosol concentrations in the surface layers are altered slightly by sublimation and wind erosion, and the concentrations are further modified as the wet season begins in late April. In contrast, soluble aerosol stratigraphy in the deeper layers remains relatively unchanged through the winter. In early summer, as melting occurs in the upper part of the snow-firn pack, meltwater carries chemical species to different depths in the underlying snow-firn layers, such that at the end of the ablation season, all of the surface cations might be leached out from the upper layers. In addition, the possible source of calcium and magnesium is discussed in this paper.