Impacts of black carbon and mineral dust on glacier melting in the Qilian Mts., northeastern Tibetan Plateau

Abstract:

 

Black carbon (BC) and mineral dust (MD), the most important composition 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 to 4950 m a.s.l. on Laohugou Glacier No.12 (LHG, 39°10′–35′ N, 96°10′–35′ E), located at Qilian Mts, 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 generally declined with the increasing elevation. The impacts 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 effect on albedo reduction than MD in this work. The impact of BC represented less than 52 % of albedo reduction while the contribution of MD was 13 % when the glacier experienced strong surficial melting and its surface was almost superimposed ice. While BC and MD contributed 20 % and 12 %, respectively, when the surface was covered by snow during summer. On average, the radiative forcing (RF) caused by BC in the snow/ice, more than MD, was 43.0 ± 36.4 W m^-2 in summer. Meanwhile, compared to glacier melting in summer of 2013 and 2014 calculated using the mass and energy balance model, i.e. 466 mm w.e. and 425 mm w.e., respectively, contribution of BC was less than 36 % of summer melting while MD and BC together contributed a maximum of 51 %. This study provided the baseline information on the concentrations and effects of BC and MD in glaciers of the northeastern boundary of the TP and their contributions in glacier melting.