Effects of Mineral Dust and Black Carbon on Albedo in the Western Greenland Ice Sheet Percolation Zone
Abstract
Recent studies have argued that the average albedo of the Greenland Ice Sheet (GIS) has been decreasing over recent decades, especially in western Greenland. Spatial and temporal variations in GIS albedo and their causes remain poorly understood due to a complex relationship between snow accumulation, optical grain size, and both mineral dust and black carbon concentrations. MODerate resolution Imaging Spectroradiometer (MODIS) satellite measurements indicate regional albedo decline over the past decade, but the cause and extent of GIS albedo change remains poorly constrained by field data. Previous studies have focused on albedo in the wet or dry snow zones, whereas here we analyze data from the rapidly changing western GIS percolation zone. As fresh snow (albedo > 0.85) warms and melts, its albedo decreases due to snow grain growth, promoting solar absorption, higher snowpack temperatures and further melt. However, dark impurities like soot and dust can also significantly reduce snow albedo, even in the dry snow zone.
Here we assess the relative importance of snow grain size and light absorbing impurity concentrations on albedo in the western GIS percolation zone. We collected broadband albedo (350-2500 nm at 3-8 nm resolution) and snow optical grain size measurements at 55 locations using an ASD FieldSpec4 spectroradiometer to simultaneously quantify radiative fluxes and spectral reflectance as part of the 4000-km Greenland Traverse for Accumulation and Climate Studies (GreenTrACS). Additionally, we collected shallow (0-50 cm) snow pit samples at ASD measurement sites to quantify black carbon and mineral dust concentrations and size distributions using a Single Particle Soot Photometer and laser-absorption particle sensor (Abakus from Klotz, Germany), respectively. Preliminary results indicate larger albedo dependence on snow grain size than on light absorbing impurities in our study area. Soot and dust concentrations in the western GIS percolation zone today appear too low to sufficiently darken the surface before being covered by additional high-albedo snow accumulation. Finally, we compare our in situ field measurements with co-located albedo data from satellites and climate models, and discuss implications for GIS surface mass balance.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.C31A..05L
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0740 Snowmelt;
- CRYOSPHEREDE: 0764 Energy balance;
- CRYOSPHEREDE: 0792 Contaminants;
- CRYOSPHERE