Impact of black carbon and mineral dust on glacier melting in central Tienshan

The light absorbing impurities (LAIs), primarily black carbon (BC) and mineral dust (MD), can darken the glacier surface, enhance radiative forcing absorption, and then accelerate glacier melting, which poses a major challenge to glacier preservation. However, a quantitative and process-based understanding of LAIs, particularly regarding their vertical distribution, enrichment mechanisms and sources, remains a critical missing component for accurately estimation of glacier melting in the Tienshan region. To address this research gap, snowpit samples were collected from the Urumqi Glacier No.1 (UG1) in the central Tienshan in August 2021 to analyze the vertical distribution of BC and MD and estimate their potential impact on glacier melting. The results showed that both BC and MD concentrations exhibited large fluctuations in the snowpit profile (Coefficient of Variation: 99.1% and 106.7%, respectively), indicating remarkable vertical variability along the snowpit depth with higher values in dust layers and infiltration ice and lower values in surface and eluviated snow layers. Backward trajectory analysis revealed that Central Asia as the primary potential source region of BC deposited on UG1. Using the SNICAR model and scenario simulations based on different snow grain size, it was estimated that LAIs contributed up to albedo reduction by 13.6% ± 8.7% and 7.9% ± 4.7%, respectively, resulting in additional glacier melt by 187.03 ± 124.29 and 108.76 ± 65.94 mm w.e. The results suggested that BC played a more important role than MD in enhancing glacier melting in the central Tienshan region. This study highlights the importance of incorporating LAI induced melt processes into regional glacier mass balance and hydrological models, further supporting to improve water resource management and assessment of transboundary pollutant transport in Central Asia.