The change of ice masses is influenced substantially by albedo (). Organic and inorganic particles reduce albedo drastically and hence, by absorbing solar energy, warm the ice surface. The supraglacial biome includes bacteria, algae and fungi. Due to damaging UV-radiation, algae protect themselves by pigmentation. This leads to a darkening of the surface, which promotes melting and hence the availability of liquid water. This again promotes the growth of algae. This change in albedo due to biological activity is called “bioalbedo” and has been described in polar regions. Bioalbedo has not yet been investigated in the Alps yet it is crucial for enhanced melting processes due to its feedback effect.
In an experimental set up, we investigated the effects of PAR and UV on algae the influence of impurities in the ice. Twelve mesocosms of filtered frozen glacier water were exposed to different radiation (UV, PAR, UV+PAR, dark) in a subzero environment. Seven are inoculated with known densities of algae biomass. Over 12 weeks I measured pigmentation, albedo, primary and secondary production and melt rate to observe the algal development in connection with a bacterial response. Results have shown that under UV and PAR the algae prosper most which lead to the lowest albedo in the mesocosm and hence showed the highest melt rates. In addition, Chlorophyll a and Astaxanthin concentrations also rose under PAR and UV light. In the treatments with only PAR, algae reacted similar but less strong. Especially regarding the secondary production and Chlorophyll a concentration there were differences between treatments with and without UV.
All in all, one can conclude that algal biomass on glaciers has an impact on its melt rates and should be investigated much more profoundly to understand the mechanisms behind glacial melt and to develop more accurate models for Alpine glaciers.