11:00 AM - 11:15 AM
[HTT16-08] The spatial variations in carbon and nitrogen stable isotopes of organic matter on the surface of Gulkana Glacier in Alaska
Keywords:carbon and nitrogen stable isotope, snow algae, glacier
Light absorbing impurities in snow and ice can reduce surface albedo and accelerate melting of snow and ice. In particular, photosynthetic algae growing on snow and ice are major constituents of the albedo reducing impurities on glaciers. The algae growing on the glacier ice surface have dark purple pigments in their cells and are mostly species of Ancylonema nordenskioeldii and Mesotaenium berggrenii. On the other hand, the algae growing on the snow surface have red pigments in their cells and are genus of Sanguina. Their distribution usually varies on a glacier, however, their controlling factors are not understood well. In this study, we investigate spatial variations in carbon and nitrogen stable isotopes of biogenic impurities on Gulkana Glacier in Alaska, where these algae dominate on glacier surface, and discuss formation process of organic matter on the glacier.
The field investigation was carried out in July of 2019 on Gulkana Glacier, which is a small mountain glacier with a total length of 4 km, locates on the Alaska Range. We collected surface ice samples and biogenic impurities at the 46 points on the glacier surface and analyzed carbon and nitrogen stable isotopes, concentrations of chlorophyll a and soluble ions, and cell volume biomass of algae.
The carbon and nitrogen stable isotopes of organic matter on the glacier ranged from -26.3 to -23.9‰ (Mean: -25.0±0.5) and from -5.7 to -2.9‰ (Mean: -3.8±0.6), respectively. They were higher in the downstream area but lower at the upstream area. This suggests that the organic matter on the glacier is not derived from a single source, but from microbial activities varied among the study sites. The chlorophyll a concentration and cell volume biomass showed that the biomass was higher and Sanguina spp. was dominant in the upstream areas whereas the biomass is lower and A. nordenskioeldiie dominated at the mid and downstream sites. The variation in the nitrogen stable isotopes is likely to reflect the sources of nitrogen used by the algae at each site. The algae in the upstream area probably assimilate the nitrogen with low nitrogen isotope ratio supplied currently from atmosphere whereas the algae in the downstream area assimilate the nitrogen with high nitrogen ratio derived from the glacier ice, which had been deposited on the glacier in the age before the Industrial Revolution.
This study revealed that the organic matter on glacier were products of various algae, which assimilate different nutrient sources depending on area of the glacier. The difference of the algal community and products may affect glacier darkening.
The field investigation was carried out in July of 2019 on Gulkana Glacier, which is a small mountain glacier with a total length of 4 km, locates on the Alaska Range. We collected surface ice samples and biogenic impurities at the 46 points on the glacier surface and analyzed carbon and nitrogen stable isotopes, concentrations of chlorophyll a and soluble ions, and cell volume biomass of algae.
The carbon and nitrogen stable isotopes of organic matter on the glacier ranged from -26.3 to -23.9‰ (Mean: -25.0±0.5) and from -5.7 to -2.9‰ (Mean: -3.8±0.6), respectively. They were higher in the downstream area but lower at the upstream area. This suggests that the organic matter on the glacier is not derived from a single source, but from microbial activities varied among the study sites. The chlorophyll a concentration and cell volume biomass showed that the biomass was higher and Sanguina spp. was dominant in the upstream areas whereas the biomass is lower and A. nordenskioeldiie dominated at the mid and downstream sites. The variation in the nitrogen stable isotopes is likely to reflect the sources of nitrogen used by the algae at each site. The algae in the upstream area probably assimilate the nitrogen with low nitrogen isotope ratio supplied currently from atmosphere whereas the algae in the downstream area assimilate the nitrogen with high nitrogen ratio derived from the glacier ice, which had been deposited on the glacier in the age before the Industrial Revolution.
This study revealed that the organic matter on glacier were products of various algae, which assimilate different nutrient sources depending on area of the glacier. The difference of the algal community and products may affect glacier darkening.