Katsumoto Seko

Structure, Formation, and Darkening Process of Albedo-reducing Material (Cryoconite) on a Himalayan Glacier: A Granular Algal Mat Growing on the Glacier

Dark-colored material (cryoconite) covering Himalayan glaciers has been reported to greatly accelerate glacier-melting by reducing surface albedo. Structure, formation, and the darkening process of the cryoconite on a Himalayan glacier were analyzed. The cryoconite was revealed to be a stromatolite-like algal mat, a product of microbial activity on the glacier. The granular algal mat contains filamentous blue-green algae (cyanobacteria) and bacteria, and grows on the ice by trapping mineral and organic particles. This structure seems to enable high algal production in nutrient poor glacial meltwater by gathering and keeping nutrient rich particles inside. The dark coloration of the mats promotes melt-hole formation on the ice (cryoconite holes), providing a semistagnant aquatic habitat for various algae and animals in the glacier. Optical and chemical analyses of the cryoconite strongly suggests that their high light- absorbency (dark coloration) is mainly due to dark-colored humic substances, residues from bacterial decomposition of the algal products and other organic matter. Our results strongly suggest that biological activity on the glacier substantially affects the albedo of the glacier surface. The structure of the algal mat seems to be important in the glacier ecosystem and biological process affecting glacier albedo.

Himalayan ice-core dating with snow algae

Snow algae in shallow ice cores (7 m long) from Yala Glacier in the Lang-tang region of Nepal were examined for potential use in ice-core dating. Ice-core samples taken at 5350 m a.s.l. in 1994 contained more than seven species of snow algae. In a vertical profile of the algal biomass, 11 distinct algal layers were observed. Seasonal observation in 1996 at the coring site indicated most algal growth occurred from late spring to late summer. Pit observation in 1991, 1992 and 1994 indicated that algal layer formation takes place annually δ 18 O, chemical ions (Na + , Cl - , SO 4 2 and NO 3 - ) and microparticles failed to show any clear seasonal variation, particularly at depths exceeding 2 m, possibly due to heavy meltwater percolation. Snow algae in ice cores would thus appear to be accurate boundary markers of annual layers and should prove useful for ice-core dating in Himalayan-type glaciers.

Superimposed ice in glacier mass balance on the Tibetan Plateau

The relations betw een mass bal ance and meltwater refre ezing were examined on the basis of glac iolo gical obse rvations carried out in summer 1993 on Xiao Dongkemadi Glacier, Tanggula Mountai ns, central Tibetan Plateau. On this glacier, a part of melt water refreezes at the snovv/ice int erface as superimp osed ice. The amount of supe rimp osed ice formation was determ ined by both meltw ater supply and temperat ure condit ion of the glaci er. Snow-lay er thic kness on the glacier ice body is less than 2 m, even in the higher accu mulat ion zone. About 60% of meltw ater generate d in the accumula tion zone for the period ?v1ay-September was trapped at the snow/ice interface by refre ezing , and was not dis charged out of the glacie r. About 26% of accumulated snow to the glacier surface was repl aced on the snow/ice interface by refreez ing in the accumulation zone. These facts indicate that superim posed ice formation is quit e signifi cant for water retention in glaciers unde r low-pre cipitation conditions.

Snow algae in a Himalayan ice core: new environmental markers for ice-core analyses and their correlation with summer mass balance

Abstract Snow algae in a shallow ice core (6.98 m long) from Yala glacier in the Langtang region of Nepal were examined for potential use as environmental markers in ice-core analysis. The ice core, taken at 5350m a.s.l. in 1994, was estimated to contain 11 annual layers from 1984 to 1994 from the profile of algal biomass. Algal biomass in each annual layer was noted to be correlated with air temperature, and the following two environmental indices which were calculated from air temperature and precipitation at Kyangjing (3920m a.s.l.), the village nearest to Yala glacier: estimated mean snow-cover thickness (MST) and estimated summer mass balance (SMB). Both parameters reflect snow-cover thickness on algal layers, which would be a major determinant of the light available for algal growth on the glacier. Snow algal biomass in the ice core appears to be a good environmental marker for indicating air temperature and accumulation during summer, which is important for understanding the mass balance of summer-accumulation-type glaciers in this region.