The evolution and environmental significance of glaciochemistry during the ablation period in the north of Tibetan Plateau, China

In order to explore the glaciochemistry of Shiyi glacier in the central Qilian Mountains, a total of 142 samples have been collected for fresh snow, surface snow, snowpit and meltwater from July 2012 to November 2013. The results indicated cations dominated the glaciochemistry, especially the high Ca2+ concentration. Relatively high Cl− and Na+ concentrations were mainly contributed by desert dust aerosols and the atmospheric aerosols from warm water bodies such as the Black, Caspian, and Aral seas. The analysis also confirmed the chemical ions in fresh snow are mainly contributed by atmospheric wet deposition. Surface snow is mainly influenced by dry deposition, and snowpits are influenced by both atmospheric deposition and leaching process, while meltwater is influenced by water–rock interactions. The profile of ionic concentration in the snowpit became more smoothed during ablation period owing to the influence of leaching. The elution sequence of the snowpit in the Shiyi Glacier was: SO42− > K+ > Ca2+ > Mg2+ > Na+ > Cl− > NO3−. The chemical concentrations for meltwater are mainly influenced by water dilution and soil thawing. The ions in snow in the central Qilian Mountains showed relatively lower concentrations than in the western Qilian Mountains, Tianshan Mountains and Altai Mountains. It was closer to balance than in glaciers in the central Tibetan Plateau, but was higher than in the southern Tibetan Plateau. Different ionic sources and dissolution process had caused the differences of chemical composition for fresh snow, surface snow, snowpit and meltwater, and these chemical compositions reflected the atmospheric background values in the northern Tibetan Plateau.