Distribution of light-absorbing impurities in snow of glacier on Mt. Yulong, southeastern Tibetan Plateau

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.