Abstract
Surface melt, driven by atmospheric temperatures and albedo, is a strong contribution of mass loss of the Greenland Ice Sheet. In the past, black carbon, algae and other light-absorbing impurities were suggested to govern albedo in Greenland’s ablation zone. Here we combine optical (MODIS/Sentinel-2) and radar (Sentinel-1) remote sensing data with airborne radar and laser scanner data, and engage firn modelling to identify the governing factors leading to dark glacier surfaces in Northeast Greenland. After the drainage of supraglacial lakes, the former lake ground is a clean surface represented by a high reflectance in Sentinel-2 data and aerial photography. These bright spots move with the ice flow and darken by more than 20% over only two years. In contrast, sites further inland do not exhibit this effect. This finding suggests that local deposition of dust, rather than black carbon or cryoconite formation, is the governing factor of albedo of fast-moving outlet glaciers. This is in agreement with a previous field study in the area which finds the mineralogical composition and grain size of the dust comparable with that of the surrounding soils.
Highlights
Surface melt of the Greenland Ice Sheet contributes to about 60% of the mass loss of the ice sheet in the past decade [1,2]
At many locations of 79 NG we find the glacier surface to be clean after the drainage of supraglacial lakes
Melt in the ablation zone of fast moving outlet glaciers in Greenland that are situated in vicinity to surrounding mountains is an important factor in ice sheet mass loss
Summary
Surface melt of the Greenland Ice Sheet contributes to about 60% of the mass loss of the ice sheet in the past decade [1,2]. Albedo itself is driven by light absorbing impurities and grain size. This effect has been important for the paleo-evolution of the Greenland Ice Sheet [3] and will remain a governing factor in future [4]. Impurities may range from insoluble light absorbing impurities (LIA) as black carbon (BC, soot), dust arising from local sources or remote deserts, algae, organic matter and fine debris, e.g., sedimentary rock particles from nearby mountains. While some impurities are directly connected to emissions from human activities, others may only be indirectly affected by anthropogenic effects, like changes in wind fields, that affect erosion and transport of debris from nearby mountains
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