The decreasing albedo of the Zhadang glacier on western Nyainqentanglha and the role of light-absorbing impurities

Abstract

Abstract.A large change in albedo has a significant effect on glacier ablation. Atmospheric aerosols -e.g. black carbon (BC) and dust -can reduce the albedo of glaciers and thus contribute to their melting. In this study, two main themes were explored: (1) the decrease in albedo of the Zhadang glacier on Mt. Nyainqentanglha between 2001 and 2012, as observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Terra satellite, and the correlation of this albedo with mass balance; and (2) The mass balance of the glacier has a positively significant correlation with its surface albedo derived from MODIS. Snow samples were collected on the Zhadang glacier to measure the BC and dust in the summer of 2012. The impacts of BC and dust on albedo reduction in 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 was a major factor in albedo reduction when the glacier was covered by newly fallen snow. Nevertheless, the contribution of dust to albedo reduction can reach as high as 56 %, much exceeding that of BC (28 %), when the glacier experiences strong surficial melting and its surface is almost bare ice. The average RF caused by dust could increase from 1.1 to 8.6 W m −2 , exceeding the RF caused by BC after snow was deposited and surface melting occurred in the Zhadang glacier. This implies that it may be dust that primarily dominates the melting of some glaciers in the inner Tibetan Plateau during melting seasons, rather than BC.

Black carbon and mineral dust in snow cover on the Tibetan Plateau

“…Studies on the TP indicate that BC has been a significant contributing factor to the observed cryospheric change Ming et al, 2009;Niu et al, 2017;Xu et al, 2009;Yang et al, 2015;Zhang et al, 2017) and a major forcer of climate change Ji, 2016). Observations and simulations also found that dust deposition on snow/ice can change the surface albedo and perturb the surface radiation balance (Ji, 2016;Qu et al, 2014), resulting in a decrease of 5-25 mm snow water equivalent (mm w.e.) over the western TP and Himalayas (Ji, 2016).…”

Concentrations and source regions of light-absorbing particles in snow/ice in northern Pakistan and their impact on snow albedo

“…However, although the values were relatively high, they were at the same level or lower than the estimates for an albedo reduction of 28 % by BC and 56 % by dust in clean ice samples and of 36 % by BC and 29 % by dust in aged snow samples, reported by Qu et al (2014) for surface samples from the Zhadang glacier, China. Simulation results by Ming et al (2013) showed BC, dust, and grain growth to reduce the broadband albedo by 11, 28, and 61 %, respectively, in a snowpack in central Tibet.…”

“…The results suggest that BC was the dominant forcing factor, rather than dust, influencing glacial surface albedo and accelerating glacier melt. BC was found to play an important role in forcing in the northern Tibetan Plateau (Li et al, 2016), whereas in the central Tibetan Plateau and the Himalayas, dust played a more important role (Qu et al, 2014;Kaspari et al, 2014). The MAC value affected the albedo more in the visible range than at 1.2 µm (nearinfrared) wavelength (Fig.…”

“…The concentrations of BC in our samples were higher than those reported by many authors (Table S2) but were comparable with the results reported by Xu et al (2012) in the Tien Shan, by Li et al (2016) in the northeast of the Tibetan Plateau, by Wang et al (2017) in northern China, and by Zhang et al (2017) in western Tien Shan, central Asia. High concentrations indicate high deposition rates on the snow and ice surface, but there are several possible reasons for a wide variation in values apart from differences in deposition rates, including differences in sampling protocols, geographical/sampling location and elevation of sampling site (Qu et al, 2014), and year/season of sampling. The majority of samples were from the ablation zone of the glaciers.…”

“…The parameters used for sensitivity analysis are shown in Table S1 in the Supplement. MAC val-ues of 7.5, 11, and 15 m 2 g −1 were selected based on a literature review (Qu et al, 2014;Pandolfi et al, 2014). In order to reduce the uncertainty, the dust concentration in the samples was divided into four diameter classes (as per the model requirements): size 1 (0.1-1.0 µm) was taken to be 2 %, size 2 (1-2.5 µm) to be 13 %, size 3 (2.5-5 µm) to be 31 %, and size 4 (5-10 µm) to be 54 % of total dust mass present in the sample, based on results published by others (Gillette et al, 1974;Mahowald et al, 2014).…”