竹内 望

Cyanobacterial communities on a glacier in the Qilian Shan, western China, were investigated using microscopic as well as 16S rRNA and internal transcribed spacer gene analyses. Microscopy revealed that there were abundant cyanobacteria on the entire glacier surface and their community consisted mainly of three morphological types. Low-cycle 16S rRNA gene sequences from six clone libraries were grouped into a total of eight cyanobacterial operational taxonomic units (OTUs), defined as 16S rRNA sequences with similarity of 99%. Although the cyanobacterial community based on morphological types displayed no significant differences among the study sites on the glacier, the community based on OTU groups varied among sites. This inconsistency may be due to simple morphology which might hide a large genetic variability. Phylogenetic analysis revealed that the OTU groups included the orders Oscillatoriales, Chroococcales and unclassified, and the majority of OTUs were Oscillatoriales. From the source environments of the cyanobacterial 16S rRNA gene sequences of each OTU on the glacier estimated by BLAST search (>97% similarity), 39.9% were from soil, 38.2% from fresh water and 1.7% from snow and ice environments. Based on geographical records in the database, all cyanobacterial OTUs were matched to those recorded from the Arctic and Antarctica. The results suggest that the cyanobacterial communities on the glacier are common in cold regions of the world and are likely not to be specialized members of the snow and ice biota but also inhabitants of soil and freshwater environments.

To clarify altitudinal changes in the bacterial community on Gulkana Glacier in Alaska, we analyzed bacterial 16S rRNA gene by low-cycle PCR amplification, denaturing gradient gel electrophoresis (DGGE), and culturing in a snowmelt medium at 4°C. Low-cycle PCR-based cloning revealed the presence of 100 bacterial OTUs; however, 41 OTUs were identified only in a single clone, suggesting that their abundance was limited because of difficulty in predominating on the glacier. In contrast, 17 major OTUs accounted for 57-87% of the clone library at each site, suggesting that they accounted for the major part of the bacteria on the glacier. In addition, five of the 17 OTUs were included in the 21 OTUs cultured in the snowmelt medium. Based on the dominant phylotypes and DGGE results, the bacterial community on the glacier could be divided into three types, corresponding to the snow-covered, snow- and ice-covered, and bare-ice areas of the glacier. Our results suggest that a relatively limited number of bacteria predominate and that each phylotype is adapted to a distinct set of conditions on the glacier.

A 51 m deep ice core was re-drilled on the Dunde Ice Cap of western China in 2002, 15 years after the previous ice core drilling in 1987. Dating by seasonal variations in delta(18)O and particle concentration showed that this 51 m deep ice core covered approximately the last 150 years. The stratigraphy and density showed that more than 90% of the ice core was refrozen ice layers, which comprised less than 5% of the annual accumulation in the older core. This indicates that the ice cap had experienced a more intense melting since 1987, possibly due to climate warming in this region. Mean net accumulation since the last drilling (2002-1987) was 176 mm a(-1), which was considerably smaller than that obtained from the 1987 core (390 mm a(-1), 1987-1963), indicating a significant decrease of net accumulation on the ice cap in the more recent period. The delta(18)O record showed an increasing trend in the late 19th century and the highest in the 1950s, which is consistent with the previous core findings. However, there has been no significant increase in delta(18)O during the last two decades, in contrast to the warming trends suggested by the melt features and other climate records. This discrepancy may be due to the modification of delta(18)O records by melt water runoff, percolation, and refreezing on the ice cap. Results strongly suggest recent significant mass loss of glaciers in the Asian high mountains and serious shortage of water supply for local people in this arid region in the near future.

Spectral reflectances in the visible to near-infrared wavelength range (350-1050 nm) were measured on the surface of Gulkana Glacier, Alaska Range, Alaska, USA, at six different elevations from May to September 2001. The measurements showed variable spectral reflectances on the glacier surface, and the spectra changed over time and elevation. The spectra in May were those of a typical wet snow surface: the reflectance ranged approximately from 0.4 to 0.8, and generally decreased as the wavelength increased. As snowmelt proceeded, the reflectance gradually fell, and specific absorptions appeared in the spectrum at wavelength ranges of 400-600 and 670-680 nm, corresponding to a red snow surface due to snow algal bloom. As the ice surface was exposed, the spectrum finally shifted to a lower (0.1-0.4) and flat reflectance curve, typical of an ice surface contaminated with dust. Analyses of the dust on the glacier surface showed that its quantity and characteristics changed spatially and seasonally and were correlated with spectral albedo. The results showed that the temporal and spatial variations in spectral reflectance on this glacier are due not only to physical properties of the glacier surface, but also to biogenic materials on the surface (e.g red-colored snow algal cells and cryoconite).

Field surveys of supraglacial ponds on debris-covered glaciers in the Nepal Himalaya clarify that ice-cliff calving occurs when the fetch exceeds similar to 80m. Thermal undercutting is important for calving processes in glacial lakes, and subaqueous ice melt rates during the melt and freeze seasons are therefore estimated under simple geomorphologic conditions. In particular, we focus on the differences between valley wind-driven water currents in various fetches during the melt season. Our results demonstrate that the subaqueous ice melt rate exceeds the ice-cliff melt rate when the fetch is >20 m and water temperature is 2-4 degrees C. Calculations suggest the onset of calving due to thermal undercutting is controlled by water currents driven by winds at the surface of the lake, which develop with expanding water surface.

Snow algae in a 45.97-m-long ice core from the Tyndall Glacier (50°59′05″S, 73°31′12″W, 1756 m a.s.l.) in the Southern Patagonian Icefield were examined for potential use in ice core dating and estimation of the net accumulation rate. The core was subjected to visual stratigraphic observation and bulk density measurements in the field, and later to analyses of snow algal biomass, water isotopes (18O, D), and major dissolved ions. The ice core contained many algal cells that belonged to two species of snow algae growing in the snow near the surface: Chloromonas sp. and an unknown green algal species. Algal biomass and major dissolved ions (Na+, K+, Mg2+, Ca2+, Cl-, SO42-) exhibited rapid decreases in the upper 3 m, probably owing to melt water elution and/or decomposition of algal cells. However, seasonal cycles were still found for the snow algal biomass,18O, D-excess, and major ions, although the amplitudes of the cycles decreased with depth. Supposing that the layers with almost no snow algae were the winter layers without the melt water essential to algal growth, we estimated that the net accumulation rate at this location was 12.9 m a- 1from winter 1998 to winter 1999, and 5.1 m from the beginning of winter to December 1999. These estimates are similar to the values estimated from the peaks of18O (17.8 m a- 1from summer 1998 to summer 1999 and 11.0 m from summer to December 1999) and those of D-excess (14.7 m a- 1from fall 1998 to fall 1999 and 8.6 m a- 1from fall to December 1999). These values are much higher than those obtained by past ice core studies in Patagonia, but are of the same order of magnitude as those predicted from various observations at ablation areas of Patagonian glaciers. © 2006 Elsevier B.V. All rights reserved.

Water samples were analyzed from ponds developed within the debris-covered area of Lirung Glacier (28 degrees 12.9 degrees N, 86 degrees 39.9 degrees E; 4000 m a.s.l.) in the Himalayas of Nepal during the pre-monsoon to post-monsoon period of 1996. Major chemical species were classified into three groups based on their relationships relative to the sum of cations: conservative (SiO2, Ca2+, K, and Alkalinity), semiconservative (Na+, Mg2+, and SO42-) and non-conservative (NH4+, NP3- and Cl-). The dominant processes determining the chemical composition of glacier pond water were sulfide oxidation coupled with carbonate dissolution and chemical weathering of aluminosilicate as indicated by the conservative and semi-conservative species. Calcium and alkalinity appeared as the dominant cation and anion, respectively, among all samples within the basin. Compared to the discharge waters at the outlet of the glacier, most of these pond waters have lower major solutes as well as alkalinity. The availability of fresh reactive minerals at the base of the glacier, coupled with higher temperature in discharge waters than in the ponds, may be the prime factors resulting in higher concentrations of most solutes in the discharge waters than in the ponds. In the ponds, higher concentrations of major solutes as well as alkalinity were observed in the monsoon than the pre-monsoon and post-monsoon seasons, suggesting the role of hydrolysis condition in chemical weathering rates. Ponds within the debris area of Lirung glacier in central Nepal Himalaya are likely to increase in importance if global warming accelerates the rate of glacial melting.

Red snow caused by algal bloom is common on glaciers and snowfields worldwide. Description of spatial distributions of snow algal blooms is important for understanding snow algae's unique life in an extremely cold environment and for determining the effect of algae through the reduction of surface albedo. Here we present the spatial distribution of red snow algae on the Harding Icefield, Alaska retrieved from a satellite image. Field observations on the icefield conducted in August 2001 revealed visible red snow, particularly near the snowline. Field measurements of spectral reflectance on the surface revealed the specific spectral absorption of algal pigments. We found a significant correlation between snow algal biomass and a reflectance ratio of SPOT ( Satellite Probatoire d' Observation de la Terre) satellite band of wavelength 610 - 680 nm to band 500 - 590 nm. Using this relationship between the reflectance ratio and algal biomass, we estimated the distribution and abundance of red snow across the icefield using a SPOT satellite image. The spatial distribution of red snow on the icefield obtained by mapping the reflectance ratio matched field observations across the icefield with more red algal blooms on the continental than the maritime side of the icefield. Area averaged mean carbon content estimated from the red algal biomass for the icefield on the image was 1.2 kg km(-2).

Two net balance records of neighboring glaciers under different conditions are analyzed to extract temporal variations in glacier melting in the Himalayas. Significant melt was observed every year at one site (wet site), whereas no melt occurred at the second site because of its high elevation (dry site). Accumulation at the wet site of a glacier is estimated from the dry site neighboring another glacier through a measured precipitation record for a short time period. The difference between the estimated accumulation and the net balances at the wet site is obtained as the "melt index, which represents the glacier melting conditions. The melt index with an interannual timescale is significant as a climatic proxy at high elevation since no relationship between stable isotopes and temperature is established and few long-term temperature records are available at high elevations in the Himalayas. The melt index showed a decadal fluctuation with a major amplitude never reported in previous studies with respect to temperature and ice cores analyses in the Himalayas. Ice cores from a site where significant melt occurs every year have not been considered available in reconstructing past climates since climatic signals in ice were disturbed by meltwater infiltration. However, we suggest a new approach to glean temperature information by a combination of wet and dry cores, not obtainable from a good-quality ice core alone. Copyright 2006 by the American Geophysical Union.

Ice-core and snow samples collected on Belukha glacier, Russian Altai mountains, were analyzed for n-alkanes by gas chromatography. On the basis of the total concentrations (T-HCs), carbon preference index (CPI) values and the plant wax contributions (WaxCn), it is suggested that mountain glaciers on the Asian continent received higher loading of n-alkanes from natural and anthropogenic sources than the Greenland ice sheet. It appears that the loading and variation of n-alkanes on glaciers in the Altai are approximately the same as those of the mountain in general, because the concentrations, CPI values and WaxCnpercentages of n-alkanes in Sofiyskiy glacier, also in the Russian Altai, are at the same levels as or slightly greater than those in ice-core and snow samples from Belukha glacier. It seems that the n-alkanes on Belukha glacier are derived mainly from higher plant wax and petroleum exhaust other than from diesel engines. Vertical profiles of T-HCs and CPI values of n-alkanes show that the non-WaxCnportions and T-HCs have recently increased with a decrease in CPI values on Belukha glacier. A similar trend of n-alkanes was reported for Sofiyskiy glacier, indicating that the influence of human activities has gradually increased around the Altai.

Several firn/ice cores were recovered from the Siberian Altai (Belukha plateau), central Tien Shan (Inilchek glacier) and the Tibetan Plateau (Zuoqiupu glacier, Bomi) from 1998 to 2003. The comparison analyses of stable-isotope/geochemistry records obtained from these firn/ice cores identified the physical links controlling the climate-related signals at the seasonal-scale variability. The core data related to physical stratigraphy, meteorology and synoptic atmospheric dynamics were the basis for calibration, validation and clustering of the relationships between the firn-/ice-core isotope/geochemistry and snow accumulation, air temperature and precipitation origin. The mean annual accumulation (in water equivalent) was 106 g cm-2 a-1 at Inilchek glacier, 69 g cm-2 a-1 at Belukha and 196 g cm-2a-1 at Zuoqiupu. The slopes in regression lines between the δ18O ice-core records and air temperature were found to be positive for the Tien Shan and Altai glaciers and negative for southeastern Tibet, where heavy amounts of isotopically depleted precipitation occur during summer monsoons. The technique of coupling synoptic climatology and meteorological data with δ18O and d-excess in firn-core records was developed to determine climate-related signals and to identify the origin of moisture. In Altai, two-thirds of accumulation from 1984 to 2001 was formed from oceanic precipitation, and the rest of the precipitation was recycled over Aral-Caspian sources. In the Tien Shan, 87% of snow accumulation forms by precipitation originating from the Aral-Caspian closed basin, the eastern Mediterranean and Black Seas, and 13% from the North Atlantic.

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 5350 ma.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 (3920 m 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.

Snow algae are cold-tolerant algae growing on snow and ice and have been reported on glaciers in many parts of the world. Blooms of snow algae can reduce the surface albedo of snow and ice and significantly affect their melting. In addition, snow algae found in ice cores can be potential indicators of the paleo-environment, making them of great interest both to the biology and the geophysics of glaciers. A snow algal community was investigated in 2002 and 2003 on Akkem glacier in the Russian Altai mountains, where no information on its biological community has previously been available. Five species of snow algae including green algae and cyanobacteria were observed on the glacier. Red snow due to a bloom of algae (Chloromonas sp.) was visually apparent in the snow area during our study periods. The total algal cell-volume biomass on the glacier ranged from 97 to 1156 mu L m(-2), which is equivalent to that reported previously on glaciers in the Himalaya and Alaska. The community structure showed that Mesotaenium berggrenii and/or Ancylonema nordenskioeldii, which are common species on glaciers in the Northern Hemisphere, were dominant in the ice area, while Chloromonas sp. was dominant in the snow area. Such community structures are similar to those on Alaskan and Arctic glaciers but differ from those on Himalayan and Tibetan glaciers, even though the Altai mountains are geographically closer to the Himalaya and Tibet than to Alaska. The difference in algal communities between the Altaic and other glaciers is discussed together with physical and chemical conditions affecting the algae.

Reliable chronologies in ice cores and snow pits from many alpine glaciers in latitudes between 60° N and 60° S are often difficult to establish owing to problems with annual-layer counting. Problems arise from melting, wind erosion and the negligible amount of precipitation in some seasons, all of which tend to obscure the seasonal variations in δ18O and chemical concentrations that are typically used to date ice cores. However, alpine glaciers contain many species of pollen grains that peak at particular times of the year. We used the peaks in Betulaceae, Pinus, Artemisia and a combination of Abies and Picea pollen species to determine the four seasonal layers of a snow pit on Belukha glacier in Russia's Altai Mountains. Comparing the pollen-dated profiles with wind and precipitation records allows us to determine where a seasonal layer is missing. Thus, the pollen-dating method described here may be a useful tool to measure the annual snow deposition on alpine glaciers, even when some seasonal layers are eroded by wind or missing due to negligible precipitation.

<title>Abstract</title>In the summers of 2001 and 2002, glacio-climatological research was performed at 4110–4120 m a.s.l. on the Belukha snow/firn plateau, Siberian Altai. Hundreds of samples from snow pits and a 21 m snow/firn core were collected to establish the annual/seasonal/monthly depth–accumulation scale, based on stable-isotope records, stratigraphic analyses and meteorological and synoptic data. The fluctuations of water stable-isotope records show well-preserved seasonal variations. The δ¹⁸O and δD relationships in precipitation, snow pits and the snow/firn core have the same slope to the covariance as that of the global meteoric water line. The origins of precipitation nourishing the Belukha plateau were determined based on clustering analysis of δ¹⁸O and d-excess records and examination of synoptic atmospheric patterns. Calibration and validation of the developed clusters occurred at event and monthly timescales with about 15% uncertainty. Two distinct moisture sources were shown: oceanic sources with d-excess &lt;12‰, and the Aral–Caspian closed drainage basin sources with d-excess &gt;12‰. Two-thirds of the annual accumulation was from oceanic precipitation, of which more than half had isotopic ratios corresponding to moisture evaporated over the Atlantic Ocean. Precipitation from the Arctic/Pacific Ocean had the lowest deuterium excess, contributing one-tenth to annual accumulation.

A 171m deep ice core from the surface to the bottom has been successfully drilled on the West Belukha snow-firn Plateau in the Russian Altai Mountains in the summer of 2003. The drill system used in this project was an electro-mechanical drill with a barrel 135cm long and 9.5cm in inner diameter manufactured by Geo Tecs Co., Japan. The maximum core length for a drilling run is 55cm. It took 87.5 hours in actual working time of 7 working days to drill the core down to the bottom of the glacier. The total number of drilling runs was 325. The mean length of the drilled core was 48.6cm. Most of the cores were not brittle and had a good cylindrical shape. High air temperature above the melting point in the drilling shelter caused some trouble in drilling. One of the major troubles was slip of cutters due to adhesion of cutting tips to the cutters and shoes.

A 45.97m-deep drilling operation was carried out during November/December 1999 on the accumulation area of Tyndall glacier (50°59′05″S, 73°31′12″W, 1756m a. s. l.) at the southern end of the Southern Patagonia Icefield. A portable electromechanical drilling system was developed for ice-coring on temperate glaciers which often have aquifers near the pore-close off depths. The firn-core obtained was subjected to visual stratigraphic observations and bulk-density measurements. Preliminary results suggest an extremely high accumulation rate (about 12-14m a^<-1> w. e.) at the drilling site. The drilling operation was strenuous because of the continuous strong wind and enormous snowfall which forced the members to survive for nearly three weeks in a snow cave before evacuation.

Two ice cores were extracted from Rikha Samba Glacier located in the central Nepal Himalayas in 1994 and 1998. Ice core quality in 1994 was poor due to cutter problems and samples were melted in situ. In 1998,a better ice core was successfully extracted and brought to Japan in frozen condition. The logistics of drilling, the transportation and preservation of ice, and problems of ice core drilling in Nepal are presented in this paper.

Biological activity on glaciers has been believed to be extremely limited. However, in Himalayan and Patagonian glaciers, we have found specialized biotic communities, including various cold-tolerant insects and copepods that were living on the glacier by feeding on algae and bacteria growing in the snow and ice. Since these microorganisms growing on the glacier surface are stored in the glacial strata every year, ice-core samples contain many layers with abundant microorganisms. In Himalayan glaciers, we studied snow algae on the glacier surface and in shallow ice cores, and showed that the layers with much snow algae in the ice core could be good boundary markers of annual layers and very useful for ice-core dating. Snow algae can be a new environmental proxy for studies of ice cores from warmer regions such as the Himalayas and Patagonia, where data on chemical and isotopic content data are not reliable because of heavy mixing.

Optical characteristics of the cryoconite collected from nine glaciers in the Himalaya, Tibet and the Arctic (Canada and Svalbard) were analyzed. The spectral light reflectance (visible region) of the cryoconite on the six glaciers in the Arctic and the Himalaya was generally low, indicating high light absorbency (dark coloration) of the cryoconite. In contrast, the spectral reflectances of the cryoconite on the three glaciers in Tibet were significantly higher than on the other glaciers. There was no significant difference in he spectral reflectance of mineral particles contained in the cryoconite between the Tibetan and the other glaciers, indicating that the difference in the albedo of the cryoconites is not due to the mineral particles, but due to organic matter contained in the cryoconite. Chemical analysis of the organic matter in the cryoconites revealed that the light absorbency of cryoconites is due to the amount of humic substances, which are dark-colored organic substances, the residue of bacterial decomposition of organic matter. The cryoconite of the three glaciers in Tibet contained significantly smaller amounts of humic substances than that of the other glaciers, probably due to different biological or chemical conditions. Results show that the formation of the humic substances in the cryoconite affects its optical characteristics, and possibly affects the surface albedo of the glaciers.

The altitudinal distribution of a snow algal community was investigated on an Alaska glacier (Gulkana Glacier in the Alaska Range) from 1270 to 1770 m a.s.l. Seven species of snow and ice algae (Chlorophyta and cyanobacteria) were observed on the glacier surface. These species were Chlamydomonas nivalis, Mesotaenium berggrenii, Ancylonema nordenskioldii, Cylindrocystis brebissonii, Raphidonema sp., and two Oscillatoriaceae cyanobacteria. The altitudinal distribution of snow algae was different among the species: Cd. nivalis was distributed on the middle to upper area, M. berggrenii; A. nordenskioldii, and one Oscillatoriaceae cyanobacterium on the middle to lower area; Raphidonema sp. on the middle area; and Cyl. brebissonii and one Oscillatoriaceae cyanobacterium on the lower area. The total cell concentration and the cell volume biomass of the snow algae ranged from 4.4 x 10(3) to 9.9 X 10(5) cells ml(-1) and from 33 to 2211 mul m(-2) respectively. The cell volume biomass changed with altitude; the biomass increased with altitude below 1600 m a.s.l., and decreased above 1600 m a.s.l. The community structure showed thatA. nordenskioldii dominated on the lower part of the glacier, and that Cd. nivalis dominated on the upper part. The species diversity was relatively high at the lowest and middle sites. The pH was 4.7 to 5.3 for snow and 4.9 to 5.7 for ice on the glacier. The altitudinal distribution of snow algae is discussed in terms of the physical and chemical condition of the glacier surface, and is compared with that on a Himalayan glacier. A larger biomass in the snow area on the Alaska glacier than that of the Himalayan glacier is likely due to less frequent snow cover in summer in Alaska. Small amounts of filamentous cyanobacteria on the Alaska glacier may allow washouts of unicellular green algae by running melt water and may cause a different pattern of altitudinal distribution of algal biomass on the ice area from the Himalayan glacier. Copyright (C) 2001 John Wiley Sons, Ltd.

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.

本総説では,今までに明らかになったヒマラヤの氷河に生息する雪氷生物の生態を紹介し,微生物による雪氷面アルベド低下効果と,微生物を使ったアイスコア分析について解説する.雪氷生物とは,氷河や雪渓などの雪氷圏に生息する低温環境に適応した特殊な生物のことをいう.ヒマラヤ氷河には,雪氷藻類と呼ばれる植物が繁殖し,その生産に支えられた動物やバクテリアが生息しており,これらの生物で構成される単純で閉鎖的な生態系が存在している.雪氷生物は,氷河の環境に適応した特有のバイオマスや群集構造の分布,また行動や生活史をもっている.ヒマラヤに多く分布する岩屑に表面を覆われたデブリカバー氷河では,氷河上湖や氷体内水系を生息場所とした生物群集が存在する.雪氷生物は,地球物理学にも重要な面があることが明らかになってきた.雪氷生物の繁殖は氷河表面のアルベド(日射光の反射率)を低下させて融解を加速し氷河変動にも影響を及ぼすこと,アイスコアに含まれる雪氷微生物の分析が新たな過去環境の指標になる可能性があることがわかってきた.

Biological characteristics of dark colored material (cryoconite) collected from Canadian Arctic glaciers (Devon and Penny ice caps) are described. The cryoconite consists of mineral particles and organic matter. The amount of organic matter was 0.8-13.8% dry weight. Seven taxa of snow algae (Chlorophyta and Cyanophyta) were observed in the cryoconite. The mineral particles, the algae, the bacteria, and amorphous organic matter formed small dark colored granules (cryoconite granules). The size of the granules was approximately 0.4mm in diameter. Microscopy of the granules revealed that the granules contain bacteria with mucus like substance, and that the surface of the granules was covered with filamentous blue-green algae. These observations suggest that the granules are formed by algal and bacterial activity on the glaciers, and that the cryoconite includes a large amount of biological products. The amount of the cryoconite per unit area on the glacier surface was generally small (mean 48g m^<-2> in dry weight). In contrast, a large amount of the cryoconite was deposited at the bottom of cryoconite holes. The small amount of cryoconite on the glacier surface means that the effect of the cryoconite on albedo reduction of the glacier surface is small.

Supraglacial lakes on a Himalayan debris-covered glacier (Khumbu Glacier in east Nepal) were investigated to identify the organisms living in them. Two kinds of insects, a copepod, a branchiopod, and nine kinds of algae were observed in the lakes. The kinds of organisms identify three types of lakes. Type A: lakes with animals and algae; Type B: lakes with animals only; Type C: lakes without living organisms. Each type of lake had distinctly different water characteristics. Suspended sediment concentration of water in Type A lakes was significantly lower than that in Type B and Type C lakes. Electrical conductivity and surface temperature of lake water was highest in Type A lakes, followed by Type B and Type C lakes. Our results suggest that the species composition in supraglacial lakes is determined by water characteristics and the life span of the lake, which may be due to debris conditions around the lake.

Snow algae in shallow ice cores (7 m long) from Yala Glacier in the Langtang 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. delta (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.

There are many supraglacial ponds on debris-covered glaciers in the Nepal Himalayas. The heat absorbed at the surface of a pond was estimated from heat budget observations on the Lirung Glacier in Langtang Valley, Nepal. The results indicated an average heat absorption of 170 W m(-2) during the summer monsoon season. This rate is about 7 times the average for the whole debris-covered zone. Analysis of the heat budget for a pond suggests that at least half of the heat absorbed at a pond surface is released with the water outflow from the pond, indicating that the water warmed in the pond enlarges the englacial conduit that drains water from the pond and produces internal ablation. Furthermore, the roof of the conduit could collapse, leading to the formation of ice cliffs and new ponds, which would accelerate the ablation of the debris-covered glacier.