5:15 PM - 7:15 PM
[MIS22-P01] Nitrogen nutrition utilized by snow-ice organisms and the origin of nitrate in the Qaanaaq Glacier, northwestern Greenland
Keywords:Glacier, Snow, Glacier ecosystem, Snow-ice organisms, Nitrate, Isotope
Snow-ice organisms that have adapted to cold environments inhabit glaciers and seasonal snow. Among these organisms, photosynthetic snow and glacier ice algae grow during summer. Nitrogen is essential for the growth of snow and glacier ice algae. However, because of the oligotrophic nature of snow and glacier surfaces, nitrogen nutrition (NH4+ and NO3-) can be a limiting factor. Therefore, describing the nitrogen conditions and their sources on snow and glacier surfaces is crucial for understanding the factors that regulate the proliferation of snow and ice algae. A previous study conducted on the glacier in mountainous regions of Central Asia suggested that the microbial activity interior of the glacier contributes to NO3- production (Hattori et al., 2023). However, the origin of nitrogen on glacier surfaces, where snow and glacier ice algae grow, remains unclear. Additionally, information on nitrogen nutrition and its origin in Arctic glaciers, where melting is accelerated by climate change, is limited. By measuring the nitrogen and oxygen stable isotopes of NO3-, it is possible to determine whether the nitrate originates from atmospheric deposition or from other processes, such as microbial activity. This study aimed to describe the nitrogen nutrition utilized by snow-ice organisms and their origins in the Qaanaaq Glacier, northwestern Greenland.
From July 26 to August 11, 2024, snow and ice samples were collected from the Qaanaaq Glacier. The snow samples included fresh white snow from the ice cap (1010 m above sea level (a.s.l.)) and red snow from the site (635 m). Ice surface samples were collected at five sites (635 m, 750 m, 860 m, 925 m, and 950 m). At each site, both clean and colored ice were collected. The collected samples were melted and filtered through GF/F filters. The NH4+ concentrations in the red snow, clean ice, and colored ice were measured using fluorometric spectrometry with o-phthalaldehyde. For the nitrogen and oxygen stable isotope analysis of NO3-, the filtrates were passed through an anion resin to concentrate NO3-, extracted with 10 mL of 1 M NaCl, and transported frozen to Kyoto University. The NO3- concentrations were measured using spectrophotometry, and NO3- was converted to N2O using the denitrifier method. The nitrogen and oxygen stable isotope ratios were measured using PT-GC-IRMS.
Measurements of nitrogen concentration revealed that sites where algal growth occurred showed lower nitrogen concentrations compared to non-algal sites, regardless of elevation. NH4+ concentrations in snow and ice samples were 0.3 ± 0.1 μM in red snow, 1.3 ± 0.7 μM in clean ice, and 0.4 ± 0.3 μM in colored ice. NO3- concentrations were 1.2 ± 0.2 μM in white snow, 0.2 ± 0.1 μM in red snow, 0.3 ± 0.1 μM in clean ice, and 0.1 ± 0.1 μM in colored ice. These results suggest that nitrogen nutrients are likely consumed by microbial activity. The nitrogen stable isotope (δ15N) of NO3- was 0.6 ± 1.7‰ in white snow, 1.0 ± 3.5‰ in clean ice, -1.4 ± 1.8‰ in red snow, and 0.6 ± 1.2‰ in colored ice. While no significant changes in δ15N were observed in colored ice across different elevations, clean ice showed a trend of decreasing δ15N with elevation. This suggests that the nitrogen sources supplied to the snow and glacier surfaces may vary with elevation. The oxygen stable isotope ratios (δ18O) were higher in white snow (68.5 ± 5.1‰) and clean ice (65.8 ± 3.0‰), whereas lower values were observed in red snow (53.1 ± 15.1‰) and colored ice (37.0 ± 8.0‰). These results indicate that the nitrogen nutrition where algal blooms occur is not derived from atmospheric deposition, but is associated with microbial activity. In conclusion, this study demonstrated for the first time that active microbial processes contribute to nitrogen production in oligotrophic environments of snow and ice surfaces.
From July 26 to August 11, 2024, snow and ice samples were collected from the Qaanaaq Glacier. The snow samples included fresh white snow from the ice cap (1010 m above sea level (a.s.l.)) and red snow from the site (635 m). Ice surface samples were collected at five sites (635 m, 750 m, 860 m, 925 m, and 950 m). At each site, both clean and colored ice were collected. The collected samples were melted and filtered through GF/F filters. The NH4+ concentrations in the red snow, clean ice, and colored ice were measured using fluorometric spectrometry with o-phthalaldehyde. For the nitrogen and oxygen stable isotope analysis of NO3-, the filtrates were passed through an anion resin to concentrate NO3-, extracted with 10 mL of 1 M NaCl, and transported frozen to Kyoto University. The NO3- concentrations were measured using spectrophotometry, and NO3- was converted to N2O using the denitrifier method. The nitrogen and oxygen stable isotope ratios were measured using PT-GC-IRMS.
Measurements of nitrogen concentration revealed that sites where algal growth occurred showed lower nitrogen concentrations compared to non-algal sites, regardless of elevation. NH4+ concentrations in snow and ice samples were 0.3 ± 0.1 μM in red snow, 1.3 ± 0.7 μM in clean ice, and 0.4 ± 0.3 μM in colored ice. NO3- concentrations were 1.2 ± 0.2 μM in white snow, 0.2 ± 0.1 μM in red snow, 0.3 ± 0.1 μM in clean ice, and 0.1 ± 0.1 μM in colored ice. These results suggest that nitrogen nutrients are likely consumed by microbial activity. The nitrogen stable isotope (δ15N) of NO3- was 0.6 ± 1.7‰ in white snow, 1.0 ± 3.5‰ in clean ice, -1.4 ± 1.8‰ in red snow, and 0.6 ± 1.2‰ in colored ice. While no significant changes in δ15N were observed in colored ice across different elevations, clean ice showed a trend of decreasing δ15N with elevation. This suggests that the nitrogen sources supplied to the snow and glacier surfaces may vary with elevation. The oxygen stable isotope ratios (δ18O) were higher in white snow (68.5 ± 5.1‰) and clean ice (65.8 ± 3.0‰), whereas lower values were observed in red snow (53.1 ± 15.1‰) and colored ice (37.0 ± 8.0‰). These results indicate that the nitrogen nutrition where algal blooms occur is not derived from atmospheric deposition, but is associated with microbial activity. In conclusion, this study demonstrated for the first time that active microbial processes contribute to nitrogen production in oligotrophic environments of snow and ice surfaces.