Impact of impurities and cryoconite on the optical properties of the Morteratsch Glacier (Swiss Alps)

Abstract

Abstract. The amount of reflected energy by snow and ice plays a fundamental role in their melting processes. Different non-ice materials (carbonaceous particles, mineral dust (MD), microorganisms, algae, etc.) can decrease the reflectance of snow and ice promoting the melt. The object of this paper is to assess the capability of field and satellite (EO-1 Hyperion) hyperspectral data to characterize the impact of light-absorbing impurities (LAIs) on the surface reflectance of ice and snow of the Vadret da Morteratsch, a large valley glacier in the Swiss Alps. The spatial distribution of both narrow-band and broad-band indices derived from Hyperion was analyzed in relation to ice and snow impurities. In situ and laboratory reflectance spectra were acquired to characterize the optical properties of ice and cryoconite samples. The concentrations of elemental carbon (EC), organic carbon (OC) and levoglucosan were also determined to characterize the impurities found in cryoconite. Multi-wavelength absorbance spectra were measured to compare the optical properties of cryoconite samples and local moraine sediments. In situ reflectance spectra showed that the presence of impurities reduced ice reflectance in visible wavelengths by 80-90 %. Satellite data also showed the outcropping of dust during the melting season in the upper parts of the glacier, revealing that seasonal input of atmospheric dust can decrease the reflectance also in the accumulation zone of the glacier. The presence of EC and OC in cryoconite samples suggests a relevant role of carbonaceous and organic material in the darkening of the ablation zone. This darkening effect is added to that caused by fine debris from lateral moraines, which is assumed to represent a large fraction of cryoconite. Possible input of anthropogenic activity cannot be excluded and further research is needed to assess the role of human activities in the darkening process of glaciers observed in recent years.

The Elbrus (Caucasus, Russia) ice core record – Part 2: history of desert dust deposition

“…with the coldest conditions present above 5200 m a.s.l., where mean summer air temperature stays below 0 • C. To characterize possible sources of aerosols deposited on glaciers, we calculated three-dimensional backward trajectories of air parcels (elementary air particles) arriving at the Elbrus plateau (5100 m a.s.l.) using the NOAA HYS-PLIT_4 trajectory model (Draxler and Hess, 1998;Stein et al, 2015) and NCEP/NCAR Reanalysis data on 2.5 • × 2.5 • grids (Kistler et al, 2001) for the 1948-2013 period. The 10 d backward trajectories were calculated for every 6 h for the whole period, resulting in a total of ∼ 100 k modelled backward trajectories.…”

“…Density plots were calculated only for 10 d backward trajectories which descended below mixed layer depth. The depth is calculated by HYS-PLIT_4 (using NCEP/NCAR Reanalysis data) for each point of backward trajectory as the height exceeding potential air temperature over surface air temperature by 2 K (Draxler and Hess, 1998).…”

Iron oxides in the cryoconite of glaciers on the Tibetan Plateau: abundance, speciation and implications

“…Measurements of light absorption were performed using an ISSW spectrophotometer in Lanzhou University, China. The experimental strategy was mainly based on the method described by Doherty et al (2010) and Wang et al (2013). The ISSW measurement system is specially designed to be sensitive to light absorption and to avoid the interference of light scattering (Grenfell et al, 2011).…”

Resolving Size Distribution of Black Carbon Internally Mixed With Snow: Impact on Snow Optical Properties and Albedo

“…Light-absorbing aerosols significantly reduce snow albedo after deposition onto snowpack (e.g., Flanner et al, 2007;Lee et al, 2017;Zhao et al, 2014), which further alters surface energy balance and hydrological cycle and hence regional climate (Menon et al, 2010;Qian et al, 2015). Black carbon (BC), the most important light-absorbing aerosol (Bond et al, 2013), has been observed as a strong driver to accelerated glacier retreat and snowmelt over high mountains (Di Mauro et al, 2017;Painter et al, 2013), midlatitude seasonal snowpack (Sterle et al, 2013;Wang et al, 2017), and polar regions (McConnell et al, 2007;Pedersen et al, 2015). The impacts of BC on snow albedo can be affected by a number of factors, including BC content in snow, BC and snow particle properties, and environmental conditions (e.g., He et al, 2014;Kokhanovsky, 2013;Räisänen et al, 2017;Warren & Wiscombe, 1980).…”