Insoluble light-absorbing impurities (ILAIs) in surface snow of glacier reduce snow albedo and accelerate glacier melt. In order to assess effects of ILAIs on glacier melt, we present the first results from field measurements of ILAIs, including black carbon (BC) and dust in snowpacks of glacier on Mt. Yulong, southeastern Tibetan Plateau (TP). Amplification factors because of snow melt were calculated for BC and dust concentrations in surface snow, and melt scavenging rates, effects of ILAIs on snow spectral albedo, and associated radiative forcing (RF) were estimated. Melt amplification generally appeared to be confined to the top few centimeters of the snowpack, and our results indicated that BC was more efficiently scavenged with meltwater than the other insoluble light absorbers (e.g., dust). Absorbing impurities reduced snow spectral albedo more with larger particulate grain radius (r(e)). Spectral albedo reduction was investigated using the SNow ICe Aerosol Radiative (SNICAR) model. Albedo reduction for 1200 ng g(-1) of BC in Mt. Yulong snow was 0.075 for snow with r(e) = 500 compared with r(e) = 200 mu m. If dust (51.37 ppm) was the only impurity in the snowpack, the spectral albedo reduction would be only 0.03, and the associated RF was 42.76 W m(-2). For a BC and dust mixed scenario, the spectral albedo was substantially reduced (0.11 +/- 0.03), and the associated RF (145.23 W m(-2)) was more than three times larger than that for the dust-only scenario. BC in snow is an active factor controlling snow albedo and snow-ice RF. Further observational studies are needed to quantify the contribution of BC and dust to albedo reduction and glacier melt and to characterize the variation of glacier RF.

The Tibetan Plateau (TP) or the third polar cryosphere borders geographical hotspots for discharges of black carbon (BC). BC and dust play important roles in climate system and Earth's energy budget, particularly after they are deposited on snow and glacial surfaces. BC and dust are two kinds of main light-absorbing impurities (LAIs) in snow and glaciers. Estimating concentrations and distribution of LAIs in snow and glacier ice in the TP is of great interest because this region is a global hotspot in geophysical research. Various snow samples, including surface aged-snow, superimposed ice and snow meltwater samples were collected from a typical temperate glacier on Mt. Yulong in the snow melt season in 2015. The samples were determined for BC, Organic Carbon (OC) concentrations using an improved thermal/optical reflectance (DRI Model 2001) method and gravimetric method for dust concentrations. Results indicated that the LAIs concentrations were highly elevation-dependent in the study area. Higher contents and probably greater deposition at relative lower elevations (generally <5000 m asl) of the glacier was observed. Temporal difference of LAIs contents demonstrated that LAIs in snow of glacier gradually increased as snow melting progressed. Evaluations of the relative absorption of BC and dust displayed that the impact of dust on snow albedo and radiatiVe forcing (RF) is substantially larger than BC, particularly when dust contents are higher. This was verified by the absorption factor, which was <1.0. In addition, we found the BC-induced albedo reduction to be in the range of 2% to nearly 10% during the snow melting season, and the mean snow albedo reduction was 4.63%, hence for BC contents ranging from 281 to 894 ng g(-1), in snow of a typical temperate glacier on Mt. Yulong, the associated instantaneous RF will be 76.38-146.96 W m(-2). Further research is needed to partition LAIs induced glacial melt, modeling researches in combination with long-term in-situ observations of LAIs in glaciers is also urgent needed in the future work. (C) 2017 Elsevier B.V. All rights reserved.