[A-CC32] Glaciology

[ACC32-02] Temporal changes of algal community in red snow on Gulkana Glacier, Alaska

*Suzunosuke Usuba ¹, Takumi Murakami², Yukihiko Onuma³, Kino Kobayashi¹, Ryohei Abe¹, Tetsuya Akabayashi¹, Ryotaro Takema¹, Nozomu Takeuchi⁴ (1.Graduate School of Science and Engineering, Chiba University, 2.School of Life Science and Technology, Institute of Science Tokyo, 3.Earth Observation Research Center, Japan Aerospace Exploration Agency, 4.Department of Earth Science, Graduate School of Science, Chiba University)

Keywords:Snow algae, Red snow

Snow algae are photosynthetic microorganisms growing on the surface of glaciers and snowpack. On alpine glaciers and snowpacks, snow algal bloom turns the snow surface to red, called red snow. This coloration is attributed to the production and accumulation of the red pigment astaxanthin, which protects algal cells from intense solar radiation. Typical red snow algal species belongs to the genus Sanguina and has been reported in glaciers worldwide. Recent studies have revealed that red snow is formed not only by Sanguinaalgae but also by the genera of Chlainomonas and Rosetta. However, the process of red snow formation involving multiple algal species remains poorly understood. Red snow reduces the albedo of snow surfaces and accelerate snow and ice melt. Therefore, understanding the growth processes of algal communities in red snow is important for evaluating its effects of albedo reduction. This study aimed to describe the temporal changes in algal communities in red snow and to infer the process of red snow formation by collecting red snow samples from the upper site of the Gulkana Glacier in Alaska from late June to late August.
The fieldwork was conducted at an altitude of 1,680 m on the Gulkana Glacier, Alaska, USA, on August 28, 2023, and June 29, July 4, and July 19, 2024. In each investigation, the snow depth was measured, and five surface snow samples were collected. The samples were stored under cold conditions and transported to the laboratory. Microscopic observations were conducted to classify algal cells morphologically, to count cell numbers, and to determine the algal community structure. Additionally, we measured nitrogen and phosphate ion concentrations in samples as algal nutrients.
In late June and early July, pale-red snow was visually observed on the glacier with snow depths of 60 cm and 57 cm, respectively. In contrast, deep-red snow was observed in late July and late August, with snow depths decreasing to 25 cm and 5 cm, respectively. Microscopic observations revealed that snow samples contained following four algal morphotypes. Type A: spherical cells likely to be Sanguina nivaloides. Type B: oval cells likely to be Chlainomonas sp. Type C: flower-shaped cells likely to be Rosetta floranivea. Type D: unidentified flagellated oval cells. The algal community structure based on cell concentration and volume revealed that in late June and early July, more than 95% of the total community was dominated by Type A (Sanguina nivaloides). By late July, the total proportion of Types B, C, and D increased to approximately 24%, and by late August, these types accounted for 87%, indicating that the algal community was diversified over the study period. The analysis of chemical solutes showed that nutrient concentrations remained low throughout the study period and there is no relationship with the observed algal community diversity. These results suggest that Sanguina algae emerge and bloom on the snow surface in the early stages of snowmelt with deeper snow depth and that Chlainomonas and Rosetta algae appear and bloom later when the depth of the snowpack became shallower. These algal groups may have different preferences in light intensity transmitted through the snowpack and in water content associated with differences in snow depth.