Biotic Acceleration of Glacier Melting in Yala Glacier 9 by vsf50303

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									             Snow and Glacier Hydrology (Proceedings of the Kathmandu Symposium, November 1992).
             IAHS Publ. no. 218,1993.                                                              309




             Biotic Acceleration of Glacier Melting in Yala
             Glacier9 Langtang Region, Nepal Himalaya


             SHIRO KOHSHIMA 1 , KATSUMOTO SEKO 2 &
             YOSHITAKA YOSHIMURA 1
             1
               Department of Science, Tokyo Institute of Technology, Ookayama, Meguro-
             ku, Tokyo 152, Japan
             2
               Institute for Hydrospheric and Atmospheric Sciences, Nagoya University,
             Chikusa-ku, Nagoya 464-01, 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 mud-like 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 1991, 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 mud-like
             material was artificially removed and the control plots with intact mud-
             like 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, 1984a, 1984b, 1985 and 1987b). 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
310                             Shiro Kohshima et al.

ablation area is covered with dark coloured mud-like material containing large
amount of algae and bacteria (Kohshima, 1984a, 1987a). Kohshima (1987a)
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 (5100-5700 m asl)
in the Langtang region of Nepal (Fig. 1) between 10 and 27 August during the
monsoon season in 1991.
     This glacier is a plateau-shaped 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
mud-like 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




                                                                          10km


                                                LANGTANG REGION
             Fig. 1 Location of Yala Glacier.
                 Biotic acceleration   of glacier melting in Yala Glacier                 311

         (a)




         (b)




               Fig. 2 Yala Glacier in monsoon season, (a) Lower part of the glacier (ablation
               area) is almost stained black by the biogenic mud-like 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 green-algae (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 mud-like 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 5100 m in altitude) during the study
312                           Shiro Kohshima et al.

period. At each point, change of surface level was measured at the
experimental plots from which the mud-like material or dirt snow layer was
artificially removed and at the control plots with intact mud-like 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 10 to 27 August
1991. Shortwave radiation and albedo were measured by a photo diode sensor
calibrated with a pyranometer.



RESULTS AND DISCUSSION

Albedo reduction by microorganisms

 The mud-like material on the surface of the ablation area mainly consisted of
blackish spherical granules (0.2-3.0 mm in diameter). The granules were
 spherical aggregations of filamentous blue-green 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 blue-green 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, 1989).
Structure and contents of dirt layer particles in the snow strata of the
accumulation area was similar to that of the mud-like granule of the ablation
area. But the diameter was much smaller (0.1-0.5 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                 313

(a)




                           lmm




(b)




           1
                  50 jim
      Fig. 3 Mud-like material.
      (a) Granular aggregation of algae and bacteria consisting the mud-like material
      covering the ablation area of the glacier. Right: intact granule; Left: ultra
      sonicated granule showing filamentous blue-green algae.
      (b) Microscopic view of the mud-like material. It contains much filamentous
      blue-green algae {Phormidium sp) and bacteria.
314                                  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 (5300-5350 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"1 in
water equivalent in the accumulation area supposing the snow density was 0.4,
and 10.6 mm day"1 at 5200 m and 17.5 mm day"1 at 5100 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.
                                                                              Int ct     c
level (cm)                                                                      ^            g"



40   _35


     .9
         *         19
20                O
                   7
                   *             2

 0                              o                                      -8
                                 *
     -                                                                 o                  -17

20   -                                                                 -28                o
                                                                       *
40                                                                                        -49

                                                                                             *
           i           1          1                                      1                   1
      5400        5350          5300                                   5200             5100
                                       a l t i t u d e (m a. s. 1. )
               Fjg. 4 Surface level change during the study period. Circle: experimental plot
               without biogenic dark material; asterisk : control plot with intact surface.



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      315

5250 m asl (Fig. 1). In the calculation, sensible heat was calculated by the bulk
method and latent heat was calculated by the bulk method assuming relative
humidity as 100%. The following formula was used for the calculation (Ohata
& Higuchi, 1980):

     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"1), T is air temperature (°C) and e is vapour
pressure (mb). Since we have no data of longwave radiation in 1991, we used
the value which taken in Yala Glacier during monsoon season in 1992. Heat
conduction from snow and ice and heat transport due to precipitation were
neglected.
     Table 1 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 10% of albedo decrease
corresponds to 17.8 W m"2 of heat gain. This amount equals to ablation rate of
4.6 mm day"1 or 137 mm/month in water equivalent. The difference of ablation
between intact and clean surface in ablation area (15.6 mm day"1) corresponds
to the difference of albedo about 30%. Considering the accumulation is about
750 mm a"1 on this glacier (Shiraiwa & Ueno, 1993) and 3 or 4 months is the
ablation season in this area (Ageta et ah, 1980), this amount (1867
mm/3month) should greatly affect the mass balance of this glacier.

Table 1 Heat balance components on the glacier at 5250 m asl.

                                                                WnT 2       Albedo
Downward shortwave radiation                                     177             -
Net shortwave radiation                                           89           0.5
                                                                 106           0.4
                                                                 124           0.3
                                                                 142           0.2
                                                                 159           0.1

Net longwave radiation (observed in 1992)                         -21            _
Sensible heat                                                       7            -
Latent heat                                                         3            -
Melting of snow and ice                                          -78          0.5
                                                                 -95          0.4
                                                                 -113         0.3
                                                                 -121         0.2
                                                                 -148         0.1
316                                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. (1980) and Ohata &
Higuchi (1980). They have carried out mass balance and heat balance studies
during monsoon season on the Glacier AX010, 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 (1980) reported that in the Glacier AX010, dark
coloured impurities on the surface reduce the albedo considerably. As the
impurities on the Glacier AX010 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 AX010 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
1991, and by a Grant-in-Aid for Scientific Research (chief: Shiro Kohshima)
from the Japan Ministry of Education, Science and Culture.


REFERENCES

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     AX010 in Shorong Himal, East Nepal, during the summer monsoon season. Seppyo 41,
     Special Issue, 34-41.
Kohshima,S. (1984a)Novelcold-tolerantinsectfoundinaHimalayanglacier. Ato«re310,225-227.
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Kohshima, S. (1985) Migration of the Himalayan wingless glacier midge (Diamesasp.) — Slope
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Kohshima, S. (1987a) Formation of dirt layer and surface dusts by micro-plants growth in Yala
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Kohshima, S. (1987b) Glacial Biology and Biotic Communities In: Evolution and Coadaptation
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Kohshima, S. (1989) Glaciological importance of microorganisms in the surface mud-like
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     Mountains, China. Bull. Glacier Res. 7, 59-65.
Ohata, T. & Higuchi, K. (1980) Heat balance study on Glacier AX010 in Shorong Himal, East
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