Concentration and size distribution of black carbon over the ablation area of Potanin glacier: enrichment ability of surface weathering granular ice of water-insoluble particles with snow/ice melting

Abstract. Light-absorbing particles on surface ice in ablation areas can accelerate glacier melting and shrinkage. A Single Soot Particle Photometer was used to measure black carbon (BC) mass concentrations (MBC) in the ablation area of Potanin Glacier, Mongolia during summer. Surface-ice MBC values (42–555 ng g−1) greatly exceeded those of surface snow (5–22 ng g−1), snow and rain (2–6 ng g−1), and surface melt water (2–11 ng g−1). Vertical profiles of MBC revealed high surface-layer concentrations, suggesting impurities trapped in the granular ice: the particularly low-density layer of the weathering crust surface. In the ablation area, MBC values of granular ice decreased with lower elevation: 134–601 ng g−1 at the 3317 m site and 8–96 ng g−1 at the 3078 m site. The fraction of residual surface BC to BC contained in lost water over a year, R, was calculated using the yearly BC deposition flux and water ablation weight Aw. Average R values were 0.17 and 0.011, respectively, at 3317 and 3078 m. Aw were 246 and 325 gw.e.cm-2, suggesting that the granular ice retains BC particles best in the upstream ablation area, showing concomitantly less capability with increasing ablation. Enriched BC on the ablation area surface comprises recent BC deposits and BC from the glacier's lower layer after rising during decades or more. Those BC emissions and deposits can therefore affect both future and present ablation area melting processes.