Abstract. Snow algal bloom is a common phenomenon on melting snowpacks in polar and alpine regions and can substantially increase snow melt rates due to the effect of albedo reduction on the snow surface. In order to reproduce algal growth on the snow surface using a numerical model, temporal changes in snow algal abundance were investigated on the Qaanaaq Glacier in north-western Greenland from June to August 2014. Snow algae first appeared at the study sites in late June, which was approximately 94 h after air temperatures exceeded the melting point. Algal abundance increased exponentially after this appearance, but the increasing rate became slow after late July, and finally reached 3.5 × 10 7 cells m −2 in early August. We applied a logistic model to the algal growth curve and found that the algae could be reproduced with an initial cell concentration of 6.9 × 10 2 cells m −2 , a growth rate of 0.42 d −1 , and a carrying capacity of 3.5 × 10 7 cells m −2 on this glacier. This model has the potential to simulate algal blooms from meteorological data sets and to evaluate their impact on the melting of seasonal snowpacks and glaciers.

In order to better understand the source of minerals on the dark-colored ice, located in the Greenland ice sheet ablation zone, we analyzed the Sr and Nd isotopic ratios of minerals in cryoconite, which were collected from glaciers in northwest and southwest Greenland. We focused on the following: (i) comparison of the isotopes of minerals in cyroconite with those in sediments from local and distant areas, (ii) regional variations in western Greenland, and (iii) spatial variations across an individual a glacier. The mineral components of the cryoconite showed variable Sr and Nd isotopic ratios ( 87 Sr/ 86 Sr: 0.711335 to 0.742406, εNd (0): −33.1 to −22.9), which corresponded to those of the englacial dust and moraine on and around the glaciers but were significantly different from those of the distant deserts that have been considered to be primary sources of mineral dust on the Greenland Ice Sheet. This suggests that the minerals within the cryoconites were mainly derived from local sediments, rather than from distant areas. The Sr ratios in the northwestern region were significantly higher than those in the southwestern region. This is probably due to geological differences in the source areas, such as the surrounding glaciers in each region. The isotopic ratios further varied spatially within a glacier (Qaanaaq and Kangerlussuaq areas), indicating that the silicate minerals on the glaciers were derived not from a single source but from multiple sources, such as englacial dust and wind-blown minerals from the moraine surrounding the glaciers.

Cryoconite granules are dark-colored biological aggregates on glaciers. Bacterial community varies with granule size, however, community change in space and their susceptibility to environmental factors has not been described yet. Therefore, we focused on bacterial community from four different granule sizes (30–249 μm, 250–750 μm, 750–1599 μm, more than 1600 μm diameter) in 10 glaciers in northwestern Greenland and their susceptibility to exogenous nutrients in cryoconite hole. A filamentous cyanobacterium Phormidesmis priestleyi, which has been frequently reported from glaciers in Arctic was abundant (10%–26%) across any size of granules on most of glaciers. Bacterial community across glaciers became similar with size increase, and whence smallest size fractions contain more unique genera in each glacier. Multivariate analysis revealed that effect of nutrients to beta diversity is larger in smaller granules (30–249 μm and 250–750 μm diameter), suggesting that bacterial susceptibility to nutrients changes with growth of granule (i.e. P. priestleyi was affected by nitrate in early growth stage).

Snow algae are cold-tolerant photosynthetic microbes growing on snow and ice. In order to investigate the factors affecting snow algal growth, the temporal changes in algal abundance on surface snow were studied over four winters in an experimental station in Niigata Prefecture, Japan, where seasonal snow is usually present from late December to early April. Snow algae appeared on the snow surface in February, and the initial algae were likely to be deposited on the snow by winds. The timing of the algal appearance varied among years, from early-February in 2011 to late-February in 2015, and is likely to be determined by a period of no snowfall and air temperatures above the melting point. Algal abundance generally increased until the disappearance of snow. The maximum algal concentration was found in 2011, which corresponds to the year when the period from algal appearance to the disappearance of snow was the longest (80 days) among the four winters. The results suggest that snow algae keep growing unless snowfall occurs and air temperature drops to freezing point, and that the algal abundance is likely to be correlated with the duration of algal growth. The algal growth curve in 2011 could be reproduced by a Malthusian model with a growth rate of 0.22 d −1.

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.