Potential Effect of Black Carbon on Glacier Mass Balance during the Past 55 Years of Laohugou Glacier No. 12, Western Qilian Mountains

This study reconstructed the annual mass balance (MB) of Laohugou Glacier No. 12 in the western Qilian Mountains during 1961-2015. The annual MB was calculated based on a temperature-index and an accumulation model with inputs of daily air temperature and precipitation recorded by surrounding meteorological stations. The model was calibrated by in-situ MB measurements conducted on the glacier during 2010-2015. Change in constructed annual MB had three phases. During Phase I (1961-1984), glacier-wide MB values were slightly positive with an average MB of 24 +/- 276 mm w.e. (water equivalent). During Phase II (1984-1995), the MB values became slightly negative with an average MB of -50 +/- 276 mm w.e.. The most negative MB values were found during Phase III (1996-2015), with an average MB of -377 +/- 276 mm w.e. Climatic analysis showed that the warming led to accelerated glacier mass loss despite a persistent increase of precipitation during the analysis period. However, an increase of black carbon deposited on the glacier surface since the 1980s could have contributed to intensified glacier melt. From simulations and measurements of MB on the Urumqi Glacier No. 1, 26% of glacier melt caused by black carbon could be identified.