Impacts of black carbon and mineral dust on radiative forcing and glacier melting during summer in the Qilian Mountains, northeastern Tibetan Plateau

Abstract. Black carbon (BC) and mineral dust (MD), the most important compositions of light absorbing particles (LAPs), significantly reduce the albedo of glaciers and thus accelerate their melting. In order to investigate the impacts of BC and MD on the glacier radiation balance and ablation, a total of 92 surface snow/ice samples were collected along different elevations from 4300–4950 m a.s.l. on Laohugou glacier No. 12 (LHG, 39°10'–35' N, 96°10'–35' E), located at Qilian Mountains, northeastern margin of the Tibetan Plateau (TP), during summer of 2013 and 2014. A thermal-optical method was employed to detect the BC (EC – element carbon) concentrations in snow/ice samples. The results showed that BC and MD concentrations were much lower in snow than those in ice, and gradually declined with increasing elevation. The effects of BC and MD on albedo reduction at different melting conditions were identified with the SNow ICe Aerosol Radiative (SNICAR) model initiated by in-situ observation data. The sensitivity analysis showed that BC had a stronger impact on albedo reduction than MD on this glacier. The impacts of BC represented around 45 % of albedo reduction while the contribution of MD was 35 % when the glacier surface presented as superimposed ice and experienced intensive melting. During summer, when the surface was covered by snow, BC and MD contributed for 15 % and 9 % respectively. On average, the radiative forcing (RF) caused by BC in the snow/ice, more than MD, was 41.6 ± 37.0 W m⁻². Meanwhile, compared to glacier melting in summer of 2013 and 2014 (409 mm w.e. and 366 mm w.e., respectively) calculated using the surface energy-mass balance model, contributions of BC and MD were less than 37 % and 32 % respectively of summer melting, while MD and BC together contributed a maximum of 61 %. This study provided the baseline information on BC and MD concentrations in glaciers of the northeastern TP and their contributions in glacier melting during summer.