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[MIS12-P10] Relationship between spectral reflectance in the visible wavelength range and the species composition and pigments of snow algae in red snow
Keywords:Red snow, Snow algae, Spectral reflectance, Mt. Naeba, Mt. Jiigatake, Northern Japanese Alps
Snow algae are cold-tolerant photosynthetic microbes growing on the surface of glaciers and snowpacks. When snow algae bloom, the snow surface is colored in green or red due to pigments in the algal cells. This phenomenon is called to as colored snow. Red colored snow can be observed in polar and alpine regions worldwide. Recent studies have revealed that red snow consists of multiple species with various pigments depending on snow conditions. However, their distribution and formation processes of red snow are still not understood well because the identification of the species and pigment composition require sample collection and laboratory analysis. The spectral reflectance of snow surface shows specific features depending on optical characteristics of impurities in the snow, including snow algal cells with various pigments. Therefore, spectral reflectance of red snow surface may provide a means of the quantification of the algal species and pigment composition in the snow and of the measurement in wide area of snowfields with remote sensing. In this study, we aimed to clarify the relationship between algal composition and spectral reflectance in red snow by conducting field investigations in the alpine regions of Mt. Naeba and Mt. Jiigatake in the Shinetsu region and the Northern Japanese Alps, where red snow occurrence had been reported.
Fieldworks were conducted on the snowpacks from May to June 2024 in the Mt. Naeba and Mt. Jiigatake located in the central part of the Honshu Island of Japan. In both areas, patches of red snow were visibly observed. Microscopy of the red snow samples collected from each site revealed that they consisted mainly of algae belonging to the genus Sanguina and Chloromonas, with their relative abundance varying among the snow surface. Spectral reflectances of red snow surfaces showed specific curves in both regions, with two distinct absorptions in the wavelength ranges of 650–700 nm and of 380–550 nm. These absorptions corresponded to the absorption ranges of typical algal pigments of chlorophyll a and b, primary carotenoids, and secondary carotenoids. There were distinct features in the wavelength range of 530–600 nm in the different red snow surfaces, which can be indicated as the inflection points of the curve ranging from 558 nm to 592 nm. A comparison of these inflection points with algal species composition showed that the inflection wavelength was positively correlated with the relative abundance of Sanguina algae. The shift in the inflection wavelength is probably due to the abundant secondary carotenoids of astaxanthin contained in Sanguina rather than Chloromonas algae. These findings indicate that the inflection point in the wavelength range of 530–600 nm in spectral reflectance can be used as a potential indicator to estimate the species and pigment composition of snow algae in red snow.
Fieldworks were conducted on the snowpacks from May to June 2024 in the Mt. Naeba and Mt. Jiigatake located in the central part of the Honshu Island of Japan. In both areas, patches of red snow were visibly observed. Microscopy of the red snow samples collected from each site revealed that they consisted mainly of algae belonging to the genus Sanguina and Chloromonas, with their relative abundance varying among the snow surface. Spectral reflectances of red snow surfaces showed specific curves in both regions, with two distinct absorptions in the wavelength ranges of 650–700 nm and of 380–550 nm. These absorptions corresponded to the absorption ranges of typical algal pigments of chlorophyll a and b, primary carotenoids, and secondary carotenoids. There were distinct features in the wavelength range of 530–600 nm in the different red snow surfaces, which can be indicated as the inflection points of the curve ranging from 558 nm to 592 nm. A comparison of these inflection points with algal species composition showed that the inflection wavelength was positively correlated with the relative abundance of Sanguina algae. The shift in the inflection wavelength is probably due to the abundant secondary carotenoids of astaxanthin contained in Sanguina rather than Chloromonas algae. These findings indicate that the inflection point in the wavelength range of 530–600 nm in spectral reflectance can be used as a potential indicator to estimate the species and pigment composition of snow algae in red snow.