[M-IS15] Mountain Science

[MIS15-P07] Autumn snow algal blooms on Tsurugi-Sawa perennial snow patch, Mt. Tateyama, Toyama-Prefecture, Japan

*Takumi Suzuki¹, Tsubasa Takahashi¹, Daiki Seto¹, Suzunosuke Usuba¹, Akane Tsushima¹, Nozomu Takeuchi¹ (1.Chiba University)

Keywords:Snow algae, Snow algal bloom, Perennial snow valley

Photosynthetic microorganisms, snow algae, inhabit the snow surface during the snowmelt season in polar and mountainous regions. Blooms of snow algae can be visibly observed on alpine snowpacks in Japan during the melting season. It has been reported mainly from spring when the snow begins to melt to summer when it disappears. For example, in Mt. Tateyama, Toyama, Japan, red-colored snow has been reported in summer (Nakashima et al., 2021). However, few reports of snow algal bloom on the snow remaining until autumn. It is essential to understand the snow algal blooms in mountainous regions of Japan to determine the conditions for snow algal growth and the ecosystem on the snowpack. This study aimed to clarify the distribution of snow algal blooms in the Tsurugisawa snow patch in Mt. Tateyama, Toyama, Japan, and discuss the algal adaptation to the intense solar radiation. We collected snow samples at three sites with different light conditions (S1, S2, S3) on the Tsurugisawa snow valley in Mt. Tateyama, Toyama, Japan, from October 7 to 9, 2021. During the study period, solar radiation and temperature changes were measured in the field. The snow algal cells in the snow samples were observed with an optical microscope in the laboratory. We also measured the concentrations of significant pigments, major dissolved chemical solutes, minerals, and organic matters in the snow samples. The snow algal blooms were observed at all the study sites as yellow-green colored snow. Microscopic observations showed that the snow algal cells in the snow samples could be classified into five main types according to the cell morphology and color. The predominant type was an oval-shaped cell that had green and orange pigments. Chlorophyll a concentrations, indicative of algal biomass, did not differ significantly among the study sites. The chlorophyll b/a ratio, which varied with light conditions, was lower in S3 than S1 and S2. The relative amounts of carotenoid pigments to chlorophyll a were significantly higher in primary carotenoids than in secondary carotenoids. It was also suggested that the de-epoxidation rate, which varies with light conditions, could differ among the study sites. The amounts of minerals significantly differed among the study sites. However, the parts of organic matter were not considerably different among the study sites. The primary dissolved chemical solutes in the snow samples suggested that ammonium ion and potassium ion were relatively higher than the ions (phosphate, nitrogen) of snow algal nutrients. In autumn, we revealed that the snow algal blooms also appear on the Tsurugisawa snow patch, Toyama, Japan. There was no significant difference in the snow algal biomass among the study sites. However, the composition of the cell types differed among the sites. The cause of spatial differences in the snow algal biomass is the lack of organic matter and the primary dissolved chemical solutes among the study sites. On the other hand, it is suggested that the snow algae adjust the chlorophyll b/a ratio and de-epoxidation ratio, rather than the production of secondary carotenoids, to protect themselves from intense solar radiation.