Glacier algae foster ice-albedo feedback in the European Alps

Abstract

the melting of glaciers and ice sheets is nowadays considered a symbol of climate change. Many complex mechanisms are involved in the melting of ice, and, among these processes, surface darkening due to organic material on bare ice has recently received attention from the scientific community. The presence of microbes on glaciers has been shown to decrease the albedo of ice and promote melting.Despite several studies from the Himalaya, Greenland, Andes, and Alaska, no quantitative studies have yet been conducted in the european Alps. in this paper, we made use of DnA sequencing, microscopy and field spectroscopy to describe the nature of glacier algae found at a glacier (Vadret da Morteratsch) of the European Alps and to evaluate their effect on the ice-albedo feedback. Among different algal species identified in the samples, we found a remarkable abundance of Ancylonema nordenskioeldii, a species that has never previously been quantitatively documented in the Alps and that dominates algal blooms on the Greenland ice Sheet. our results show that, at the end of the ablation season, the concentration of Ancylonema nordenskioeldii on the glacier surface is higher than that of other algal species (i.e. Mesotaenium berggrenii). Using field spectroscopy data, we identified a significant correlation between a reflectance ratio (750 nm/650 nm) and the algae concentration. This reflectance ratio could be useful for future mapping of glacier algae from remote sensing data exploiting band 6 (740 nm) and band 4 (665 nm) of the MultiSpectral Instrument (MSI) on board Sentinel-2 satellite. Here we show that the biological darkening of glaciers (i.e. the bioalbedo feedback) is also occurring in the european Alps, and thus it is a global process that must be taken into account when considering the positive feedback mechanisms related to glacier melting.Glaciers and ice sheets are not lifeless 1 . It has been demonstrated that several species of microorganisms, algae and small arthropods find their optimal environment on melting ice and snow. These organisms are also able to shape their environment, through a feedback cycle that involves the albedo. In fact, since these organisms are darker than snow and ice, their presence increases the light absorption and promotes the melting of underlying snow or ice 2-4 . On the surface of glaciers, such extremophiles often aggregate with inorganic material (i.e. mineral dust) to form cryoconite 5,6 . Cryoconite is a dark sediment 5,7 that increases the absorption of visible radiation 4,8 , and promotes the formation of characteristic cryoconite holes 9 which are globally recognized as an hot spot of biodiversity on ice 10 . Besides living organisms, cryoconite is known to concentrate pollutants such as contaminants and radionuclides 11,12 . This may represent a problem in the future, with a possible secondary release of these substances to the environment 13,14 .Cryoconite accumulated in cryoconite holes has a limited impact on glacier and ice sheet surface mass balance. Instead, the presen...

Seasonal and Interannual Variability of Melt-Season Albedo at Haig Glacier, Canadian Rocky Mountains

“…Albedo measurements from the upper ablation area of Haig Glacier over the period 2002-2017 indicate significant interannual variability in mean melt-season and glacier ice albedo, but there is no temporal trend in surface albedo over this period. This runs counter to documented albedo reductions elsewhere (Oerlemans et al, 2009;Mernild et al, 2015;Williamson et al, 2019;di Mauro et al, 2020), and to anecdotal evidence of darkening glaciers in the Canadian Rockies. The result may just be specific to the Haig Glacier AWS site; we do not have data to constrain albedo trends on the lower glacier, where changes and melt 550 feedbacks have been strongest over the observation period.…”

Glacier albedo reduction and drought effects in the extratropical Andes, 1986–2020

“…Alternatively, some contribution of albedo reduction in this region may be attributable to the presence of algae and microbial communities in snow and cryoconite (e.g. Di Mauro and others, 2020) thereby enhancing the positive feedback of glacier melting. Again, to date, no known studies have demonstrated this within the central Andes and it is unclear to what extent such glacier-algae communities affect small mountain glaciers of the semi-arid region.…”

Application of an improved surface energy balance model to two large valley glaciers in the St. Elias Mountains, Yukon

“…Combined with the relative complexity of the model, it is best-suited to catchment-scale applications where high-quality in situ data are already available to better understand the volume and spatial and temporal distribution of meltwater production throughout the melt season. Since we derive distributed surface albedo from Landsat 8 data, the model also has wide applicability to further investigate the impacts of the darkening of mountain glaciers (Naegeli and Huss, 2017; Di Mauro and others, 2020) and ice sheets (Box and others, 2012; Bond and others, 2013; Dumont and others, 2014; Williamson and others, 2019; Tedstone and others, 2020).…”