Abstract
Abstract. Surface albedo of snow and ice is substantially reduced by inorganic impurities, such as aeolian mineral dust (MD) and black carbon (BC), and also by organic impurities, such as microbes that live in the snow. In this paper, we present the temporal changes of surface albedo, snow grain size, MD, BC and snow algal cell concentration observed on a snowpack in northwest Greenland during the ablation season of 2014 and our attempt to reproduce the changes in albedo with a physically based snow albedo model. We also attempt to reproduce the effects of inorganic impurities and the red snow algae (Sanguina nivaloides) on albedo. Concentrations of MD and red snow algae in the surface snow were found to increase in early August, while snow grain size and BC were found to not significantly change throughout the ablation season. Surface albedo was found to have decreased by 0.08 from late July to early August. The albedo simulated by the model agreed with the albedo observed during the study period. However, red snow algae exerted little effect on surface albedo in early August. This is probably owing to the abundance of smaller cells (4.9×104 cells L−1) when compared with the cell abundance of red snow reported by previous studies in the Arctic region (∼108 cells L−1). The simulation of snow albedo until the end of the melting season, with a snow algae model, revealed that the reduction in albedo attributed to red snow algae could equal 0.004, out of a total reduction of 0.102 arising from the three impurities on a snowpack in northwest Greenland. Finally, we conducted scenario simulations using the snow albedo model, coupled with the snow algae model, in order to simulate the possible effects of red snow blooming on snow albedo under warm conditions in northwest Greenland. The result suggests that albedo reduction by red snow algal growth under warm conditions (surface snow temperature of +1.5 ∘C) reached 0.04, equivalent to a radiative forcing of 7.5 W m−2 during the ablation season of 2014. This coupled albedo model has the potential to dynamically simulate snow albedo, including the effect of organic and inorganic impurities, leading to proper estimates of the surface albedo of snow cover in Greenland.
Highlights
The Greenland Ice Sheet, which is the largest continuous body of ice in the Northern Hemisphere, has been losing mass rapidly since the 2000s (Rignot et al, 2008)
Because a reduction of snow albedo increases the absorption of solar radiation by a snowpack, the reduction in albedo accelerates the melting of snow
Snow algae visibly bloomed on the snowpack at the study site from late July to August in 2014. They consisted mostly of the spherical red cells of S. nivaloides, and their mean diameter was 21.3 ± 2.3 μm (Onuma et al, 2018), there was no molecular analysis of all species present
Summary
The Greenland Ice Sheet, which is the largest continuous body of ice in the Northern Hemisphere, has been losing mass rapidly since the 2000s (Rignot et al, 2008). The increase in the melting of snow and ice is likely to be caused by reduction of surface albedo as well as temperature rise (Tedesco et al, 2011; Box et al, 2012; Yallop et al, 2012). It is important to understand the physical processes causing the reduction in albedo and to estimate current and future snow and ice albedo accurately on the Greenland Ice Sheet. Surface albedo plays an important role in the balance of energy over the snow surface.
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