Snow and Glacier Hydrology (Proceedings of the Kathmandu Symposium, November 992). IAHS Publ. no. 28,993. 309 Biotic Acceleration of Glacier Melting in Yala Glacier 9 Langtang Region, Nepal Himalaya SHIRO KOHSHIMA, KATSUMOTO SEKO 2 & YOSHITAKA YOSHIMURA Department of Science, Tokyo Institute of Technology, Ookayama, Meguroku, Tokyo 52, Japan 2 Institute for Hydrospheric and Atmospheric Sciences, Nagoya University, Chikusaku, Nagoya 4640, Japan Abstract In some Himalayan glaciers, the microbial production on the glacier surface is so large during the monsoon season that the surface of the ablation area is covered with a dark coloured mudlike material which mainly consists of algae and bacteria. This material reduces the surface albedo of the glacier and accelerates glacier melting. During the monsoon season in 99, the impact of this process was assessed at Yala Glacier in Langtang region, Nepal. At several elevations on the glacier, the rates of surface melting at the experimental plots from which the mudlike material was artificially removed and the control plots with intact mudlike material were recorded by stake measurements. The result showed that the rates of surface melting at the control plots covered with biogenic dark coloured material were considerably larger than those at the experimental plots. In the ablation area, especially, melting rates at the control plots were about 3 times larger than those at the experimental plots. The heat balance, calculated from the meteorological data recorded on the glacier, suggests that most of the ablation (about 90%) is attributed to net radiation. These results suggest that the biotic albedo reduction considerably affects the heat balance and mass balance in this type of glacier. INTRODUCTION Himalayan glaciers are never abiotic environments. They are simple and well closed ecosystems; housing various microbes, insects and copepods living in the glacier ice (Kohshima, 984a, 984b, 985 and 987b). In this ecosystem, the activities of living things are influenced by physical and chemical characteristics of the glacier, and, on the other hand, it is possible that physical and chemical characteristics of the glacier are affected by the activities of living things. In some Himalayan glaciers, for example Yala Glacier in Langtang region, Nepal, the microbial production which sustains the animal community of this ecosystem becomes so large during the monsoon season that the surface of the
30 Shiro Kohshima et al. ablation area is covered with dark coloured mudlike material containing large amount of algae and bacteria (Kohshima, 984a, 987a). Kohshima (987a) suggested that in this glacier, the dark coloured products of the microbes accelerate the surface melting of the glacier by reducing the surface albedo. However, quantitative study of this process has not been made yet. This study aims to clarify the biotic process on the glacier and its effect on heat balance and mass balance. FIELD DESCRIPTION AND METHODS The research was carried out at Yala (Dakpatsen) Glacier (5005700 m asl) in the Langtang region of Nepal (Fig. ) between 0 and 27 August during the monsoon season in 99. This glacier is a plateaushaped small glacier without rock debris cover. The equilibrium line in the study period was at ca. 5300 m in altitude. Though the accumulation area was covered with snow during the study period, there was no snow cover on the surface of the ablation area. During the study period, the ice surface of the ablation area was covered with dark coloured mudlike material containing large numbers of microbes, so that the lower half of the glacier surface seemed to be painted black (Fig. 2(a)). In the snow strata of the accumulation area, dark coloured snow layers (dirt layers) containing organic and inorganic small particles (dirt layer particles) were observed. At LANGTANG REGION LANGTANG LI LANGTANG REGION 0km Fig. Location of Yala Glacier.
Biotic acceleration of glacier melting in Yala Glacier 3 (a) (b) Fig. 2 Yala Glacier in monsoon season, (a) Lower part of the glacier (ablation area) is almost stained black by the biogenic mudlike material, (b) Uppermost dirt layer containing microbes appeared to the surface after heavy ablation. the beginning of the study period, the uppermost dirt layer appeared on the surface because of the high ablation, and the surface was partly tinted pale orange by a bloom of red coloured greenalgae (Fig. 2(b)). But the surface was soon covered by new snow after the next snow fall. These dark coloured materials were sampled at many points on the glacier, and their structure and contents were analysed. To assess the effect of mudlike material and dirt layer particles on the glacier melting, stake measurements as follows were carried out at five points (5400 m, 5350 m, 5300 m, 5200 m and 500 m in altitude) during the study
32 Shiro Kohshima et al. period. At each point, change of surface level was measured at the experimental plots from which the mudlike material or dirt snow layer was artificially removed and at the control plots with intact mudlike material or dirt snow layers, and the results were compared. To assess the impact of albedo change on heat balance and mass balance of this glacier, meteorological data (shortwave radiation, temperature and wind velocity) were recorded on the ablation area (5250 m asl) from 0 to 27 August 99. Shortwave radiation and albedo were measured by a photo diode sensor calibrated with a pyranometer. RESULTS AND DISCUSSION Albedo reduction by microorganisms The mudlike material on the surface of the ablation area mainly consisted of blackish spherical granules (0.23.0 mm in diameter). The granules were spherical aggregations of filamentous bluegreen algae and bacteria, with some pale coloured fine mineral grains, wind blown organic fragments and unicellular green algae tightly bound by the long algae filaments (Fig. 3(a)). The most abundant algae were a filamentous bluegreen algae (Phormidium spp.) which associated with much blackish bacteria (Fig. 3(b)). Some unicellular green algae (Clamydomonas sp. etc.) were also found. The percentage of organic matter in these granules, most of which was found to be microbes, ranged from 4.8% to 22.0% in dry weight (Kohshima, 989). Structure and contents of dirt layer particles in the snow strata of the accumulation area was similar to that of the mudlike granule of the ablation area. But the diameter was much smaller (0.0.5 mm) and smaller numbers of microbes were present. The albedo of the glacier was substantially decreased by these blackish materials. In the ablation area, the albedo varied from a few percent to 30% according to the amount of these dirt particles. Most of the dirt covered area has albedo less than 5%. The albedo of these surfaces is very low compared with the albedo of a bare ice surface (ca. 40%). The albedo of the uppermost dirt layer appearing on the surface of the accumulation area, ranged from 20% to 50%, well below the albedo of white snow (70%90%). Considering that living microbes contain much water and that their specific gravities must be much smaller than those mineral grains, the volume of the microbes in wet granules is much larger than that of mineral grains. Since most of mineral grains had transparent or pale colorations and their surface was covered by many microbes, the dark colorations of these granules should be due to the colour of microbes. By covering the surface of pale coloured mineral grains, these microbes might be able to darken the calor of the material and decrease the albedo of the glacier very effectively.
Biotic acceleration of glacier melting in Yala Glacier 33 (a) lmm (b) 50 jim Fig. 3 Mudlike material. (a) Granular aggregation of algae and bacteria consisting the mudlike material covering the ablation area of the glacier. Right: intact granule; Left: ultra sonicated granule showing filamentous bluegreen algae. (b) Microscopic view of the mudlike material. It contains much filamentous bluegreen algae {Phormidium sp) and bacteria.
34 Shiro Kohshima et al. Effects of the biogenic dirt materials on glacier melting Figure 4 shows the surface level change during the study period, recorded at five different elevations on the glacier. It shows that the equilibrium line in this period lies between SM2 and SM3 (53005350 m asl) and that at all elevations on the glacier, the rate of melting at the control plots (circle) exceeded that of experimental plots (asterisk). Especially in the ablation area (lower than 5300 m asl), total decrease of the surface level at the control plots was about three times larger than that of the experimental plots. The fact that also in the accumulation area (higher than 5300 m asl) melting at the control plots exceeded that of experimental plots, indicates that dirt layer particles could accelerate melting even under the thin snow cover. Differences in melting rates between the experimental plot and the control plot was about 2.5 mm day" in water equivalent in the accumulation area supposing the snow density was 0.4, and 0.6 mm day" at 5200 m and 7.5 mm day" at 500 m supposing the ice density was 0.9. Considering the ablation season in this area is 3 or 4 month, this amount should considerably affect the mass balance of this glacier. The results clearly show the importance of biogenic dirt materials in ablation process of this glacier. level (cm) Int^ct c g" 40 20 0 20 _35.9 9 O 7 2 o 8 o 28 7 o 40 i 5400 5350 5300 5200 500 altitude (m a. s.. ) Fjg. 4 Surface level change during the study period. Circle: experimental plot without biogenic dark material; asterisk : control plot with intact surface. 49 Impact of the biotic albedo reduction on heat and mass balance of the glacier To clarify the impact of biotic albedo reduction on mass balance of this glacier, the heat balance was calculated from the meteorological data set recorded at
Biotic acceleration of glacier melting in Yala Glacier 35 5250 m asl (Fig. ). In the calculation, sensible heat was calculated by the bulk method and latent heat was calculated by the bulk method assuming relative humidity as 00%. The following formula was used for the calculation (Ohata & Higuchi, 980): SH = 3.03 x V x T LH = 4.76 x e x T where SH and LH are sensible heat and latent heat flux to glacier respectively (W m" 2 ), V is wind velocity (m s" ), T is air temperature ( C) and e is vapour pressure (mb). Since we have no data of longwave radiation in 99, we used the value which taken in Yala Glacier during monsoon season in 992. Heat conduction from snow and ice and heat transport due to precipitation were neglected. Table shows heat balance components of Yala Glacier. The results show that the contribution of shortwave radiation is considerably large compared with other terms. It is due to the weakness of wind velocity and temperature near freezing point. Therefore, melting of this glacier is largely controlled by die albedo. The heat balance calculation shows that 0% of albedo decrease corresponds to 7.8 W m" 2 of heat gain. This amount equals to ablation rate of 4.6 mm day" or 37 mm/month in water equivalent. The difference of ablation between intact and clean surface in ablation area (5.6 mm day" ) corresponds to the difference of albedo about 30%. Considering the accumulation is about 750 mm a" on this glacier (Shiraiwa & Ueno, 993) and 3 or 4 months is the ablation season in this area (Ageta et ah, 980), this amount (867 mm/3month) should greatly affect the mass balance of this glacier. Table Heat balance components on the glacier at 5250 m asl. Downward shortwave radiation Net shortwave radiation Net longwave radiation (observed in 992) Sensible heat Latent heat Melting of snow and ice WnT 2 77 89 06 24 42 59 2 7 3 78 95 3 2 48 Albedo 0.5 0.4 0.3 0.2 0. _ 0.5 0.4 0.3 0.2 0.
36 Shiro Kohshima et al. The relationship between heat balance and mass balance of another glacier in the Nepal Himalaya has been investigated by Ageta et al. (980) and Ohata & Higuchi (980). They have carried out mass balance and heat balance studies during monsoon season on the Glacier AX00, Shorong Himal. They showed that heat balance on this glacier is mainly determined by net radiation. Especially, albedo on the glacier is essential to determine the amount of glacier melting. Ohata & Higuchi (980) reported that in the Glacier AX00, dark coloured impurities on the surface reduce the albedo considerably. As the impurities on the Glacier AX00 collected by Seko (one of present authors) also contains much amount of microbes similar to those of Yala Glacier (Kohshima, unpublished), biotic acceleration of the glacier melting might occur in this glacier, too. Glacier AX00 is a similar to Yala Glacier in its size, shape and elevation. Both are plateau shaped, small glaciers without rock debris cover. Such Himalayan glaciers have been categorized as Clean Type Glacier (C type) and other valley glaciers with rock debris cover as Dirty Type Glacier (D type). Our study suggests that some of C type glaciers are, in fact, not clean and darkly coloured by biotic activity. Therefore, for the precise estimation of melting rate on this type of glacier in the Nepal Himalayas, it is necessary to understand the formation process and nature of biogenic dark coloured material. Acknowledgements The authors would like to express appreciation to the staff of the Department of Hydrology and Meteorology, Ministry of Water Resources, Nepal Government. We are very much obliged to the Sherpa people and people of Langtang village who helped our work in Nepal, especially in Langtang Valley. This study was aided by the Moritani foundation for Science 99, and by a GrantinAid for Scientific Research (chief: Shiro Kohshima) from the Japan Ministry of Education, Science and Culture. REFERENCES Ageta, Y., Ohata, T., Tanaka, Y., Ikegami, K. & Higuchi, K. (980) Mass balance of Glacier AX00 in Shorong Himal, East Nepal, during the summer monsoon season. Seppyo 4, Special Issue, 344. Kohshima,S. (984a)NovelcoldtolerantinsectfoundinaHimalayanglacier. Ato«re30,225227. Kohshima, S. (984b) Living microplants in the dirt layer dust of Yala glacier. Bull. Glacier Res. 3, 997. Kohshima, S. (985) Migration of the Himalayan wingless glacier midge (Diamesasp.) Slope direction assessment by suncompassed straight walk. J. Ethology 3, 9304. Kohshima, S. (987a) Formation of dirt layer and surface dusts by microplants growth in Yala glacier, Nepal Himalaya. Bull. Glacier Res. 5, 6368. Kohshima, S. (987b) Glacial Biology and Biotic Communities In: Evolution and Coadaptation in Biotic Communities (ed. by S. Kawano et al), 7692. University of Tokyo Press. Kohshima, S. (989) Glaciological importance of microorganisms in the surface mudlike materials and dirt layer particles of the Chongce Ice Cap and Gozha Glacier, West Kunlun Mountains, China. Bull. Glacier Res. 7, 5965. Ohata, T. & Higuchi, K. (980) Heat balance study on Glacier AX00 in Shorong Himal, East Nepal. Seppyo 4, Special Issue, 4247.