Distribution of major elements between the dissolved and insoluble fractions in surface snow at Urumqi Glacier No. 1, Eastern Tien Shan

A total of sixty-three surface snow samples collected at Urumqi Glacier No. 1 (UG1), Eastern Tien Shan between March 2006 and December 2007 were analyzed for the concentrations of Na, K, Mg, and Ca in the dissolved and insoluble fractions by ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. The dissolved and insoluble concentrations of these four major elements showed significantly positive correlation (coefficients 0.7 ~ 1.0, p < 0.0001) with the concentration of insoluble Al (a reference element of the upper continental crust), suggesting that the four elements were mainly derived from crustal materials. The median dissolved fraction percentage (DFP, calculated as dissolved/(dissolved + insoluble) × 100%) was 67.1% and 35.7% for Ca and Na, respectively, but only 16.8% and 8.9% for Mg and K, respectively. This suggests that Ca and Na were more readily released into the meltwater than were Mg and K from mineral dust in the UG1 snow. The elution sequence through the surface snow was determined to be Ca > Na > Mg > K by the change of DFP. The temporal variability of DFP was attributed to different processes, such as dry/wet deposition in the atmosphere and the post-depositional melting and elution in snow. The DFPs were relatively stable during the dry/cold season (December through March) due to predominantly dry deposition and infrequent elution, whereas they varied significantly during the wet/warm season (April through November) because DFP was modified by wet deposition (which will increase DFP) and the elution process (which will reduce DFP). Our results reveal that DFP can provide a new insight into the understanding and explanation of ice core records, and basic information for evaluating the impact of atmospheric dust on biogeochemical cycles.