Ice Darkening on Turner Glacier in Auyuittuq National Park, Nunavut: A Characterization of Surface Algal Blooms and the Associated Implications for Glacier Albedo and Melt

The Arctic is the largest regional source of land ice to global sea-level rise, composing 31% of the global eustatic sea-level contributions since 1992. Within the Arctic, the glaciers of the Canadian Arctic are the third largest contributor. The presence of light absorbing particles (LAPs) on glaciers, such as mineral dust, ash, and algae, have been shown to lower the albedo of ice, leading to an increase in the absorption of incoming solar radiation, promoting melt. While surface algal blooms and their albedo-reducing effect has been quantified on glaciers in western Canada, Alaska, the European Alps, and southwestern Greenland, it is currently unknown if, or to what extent, either of these phenomena are occurring in the Canadian Arctic. This study employs light microscopy and field spectroscopy to characterize surface algal blooms found on Turner Glacier in Auyuittuq National Park, Nunavut, and to evaluate the associated effect on albedo. From ice samples, an average algal cell abundance of 6.1 x 104 cells/mL was found, with Mesotaenium berggrenii as the dominant species, followed by Ancylonema nordenskioeldii, among the six identified species. Additionally, a significant negative relationship between broadband albedo and algal cell abundance (R2 = 0.67, p = 0.0001) was observed, confirming, for the first time, that the algal-albedo effect is occurring in the Canadian Arctic. The relationship between cell abundance and spectral reflectance was quantified by integrating cell counts with in-situ spectroradiometer measurements (320nm-1100nm), to develop a field-calibrated, remote sensing index. When combined with satellite imagery from the MultiSpectral Instrument (MSI) aboard Sentinel-2, this index will support the future large-scale mapping of glacier algae. Together, these findings fill an important geographical knowledge gap that will inform and improve the characterization, remote detection, and monitoring of surface algal blooms on glaciers in the Canadian Arctic, and their implications for albedo and melt.