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Melting of Himalayan glaciers can be accelerated by the deposition of airborne black carbon and mineral dust as it leads to significant reductions of the surface albedo of snow and ice. Whereas South Asia has been shown a primary source region to these particles, detailed sources of these aerosol pollutants remain poorly understood. In this study, the chemical compositions of snow pit samples collected from Jima Yangzong glacier in the central Himalayas were analyzed to obtain information of atmospheric aerosols deposited from summer 2009 to spring 2010. Especially, an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was used for the first time to chemically characterize the dissolved organic and inorganic matter (DOM and DIM) in snow samples. The concentrations of these species varied seasonally, with high levels observed during the winter-spring period and low levels during the summer monsoon period. On average, the dissolved substances was dominated by organics (58%) with important contributions from inorganic species, NO3(-) (12.5%), Ca(2+) (9.1%), NH4(+) (8.7%), and SO(4)(2-) (8.1%). DOM was found more oxidized with an average (± 1σ) atomic oxygen-to-carbon ratio (nO/nC) of 0.64 (± 0.14) and organic mass-to-carbon ratio (OM/OC) of 2.01 (± 0.19) during the winter-spring periods compared to the summer season (nO/nC = 0.31 ± 0.09 and OM/OC = 1.58 ± 0.12). In addition, biomass burning particles were found significantly enhanced in snow during the winter-spring periods, consistent with HYSPLIT back trajectory analysis of air mass history, which indicates prevailing atmospheric transport from northwest India and Nepal.

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Globally, alpine glaciers hold a large quantity of dissolved organic matter (DOM) and are headwaters of numerous rivers supporting downstream heterotrophic metabolism. However, it remains unclear how glacial coverage and distance from the glacial terminus affect the fate of DOM. Here, we elucidate DOM variability in glacial-fed streams on the Tibetan Plateau using field sampling and bioincubation experiments and compare our findings with the existing literature. We found that dissolved organic carbon, DOM absorption a(254), DOM aromaticity, and the relative abundance of lignin compounds in glacial-fed streams and rivers all increased with increasing distance from the glacial terminus and with decreasing glacial coverage. We also found that contribution of protein-like components, the relative abundance of aliphatic compounds, and DOM biolability increased with increasing glacial coverage and with decreasing distance from the glacial terminus. The ratio of glacial coverage to the logarithmic transformed distance from the glacial terminus was better than that of actual glacial coverage and distance from the glacial terminus in tracing the variability of glacial-fed stream DOM. Microbes in surface ice can produce biolabile DOM that is exported downstream with meltwater. This glacial-fed stream and river DOM is an important source of the highly bioavailable material fueling downstream heterotrophic activity.

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Temporal variation of runoff chemistry and its seasonal controls relating to chemical weathering processes and drainage system evolution were examined at Urumqi Glacier No.1 in Xinjiang, China, over a full melt season. The dominant ions in meltwater runoff are HCO 3 − , Ca 2+ , and SO 4 2− ; and Fe, Sr, and Al are dominant elements. Concentrations of major ions and some elements show periodic variations with seasons and negatively correlate with discharge, whereas other elements (e.g., Al, Ni, Cu, Zn, Cd, and Pb) show a random change, providing insights into the hydrological and physicochemical controls. HCO 3 − and Ca 2+ are primarily derived from calcite, SO 4 2− and Fe mainly come from pyrite, and Sr and Al principally originate from silicate.Hydrochemical fluxes of solutes exhibit strong seasonality but are positively related to discharge, suggesting an increasing release of solutes during higher flow conditions. Solute yields, cation denudation rate, and chemical weathering intensity observed at Urumqi Glacier No.1 are higher than those at most basins worldwide.This suggests that chemical weathering in central Asia may be stronger than at other glacial basins with similar specific discharge. Concentrations of some elements (e.g., Fe, Al, As, Pb, and Zn) are close to or exceed the guidelines for drinking water standards in meltwater-fed rivers. These rivers may face future challenges of water quality degradation, and relationships between changing flow and water quality conditions should be established soon, given that development of channelized flow is expected to be earlier over a melt season in a warming climate.