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Characteristics of Surface Dust on Ürümqi Glacier No. 1 in the Tien Shan Mountains, China

Characteristics of Surface Dust on Ürümqi Glacier No. 1 in the Tien Shan Mountains, China Zhongqin Li{ Monitoring studies show that many mountain glaciers worldwide are decreasing in mass. An important component of the process of ice mass loss is the effect of dust on *Corresponding author: Department of albedo and its effect on glacier mass balance. The characteristics of surface dust were Earth Sciences, Graduate School of Science, Chiba University, 1-33, investigated in August 2006 on the Uru ¨ mqi Glacier No. 1 in the Tien Shan Yayoicho, Inage-ku, Chiba-city, Chiba Mountains, China. The bare ice surface of the glacier was mostly covered by brown 263-8522, Japan dust. The amounts of surface dust on the ice surface (dry weight) ranged from86to ntakeuch@faculty.chiba-u.jp 22 22 1113 g m (mean: 335 g m , standard deviation: 5 211), which is within the {Laboratory of Cryosphere and normal range for Asian glaciers, but significantly greater than those on glaciers in Environment/Tien Shan Glaciological Station, Cold and Arid Regions other regions such as Alaska, Patagonia, and the Canadian Arctic. An analysis of Environmental and Engineering organic matter and microscopy of the surface dust revealed that the dust contained Research Institute, Chinese Academy of high levels of organic matter, including living cyanobacteria. This suggests that it is Sciences, 320 Donggang West Road, comprised not only of deposits of wind-blown desert dust, but is also a product of Lanzhou 730000, China microbial activity on the glacier itself. Spectral albedo of the glacial surface showed lizq@lzb.ac.cn spectrum curves typical of those of snow and ice contaminated with dust. The integrated surface albedo ranged from 0.09 to 0.24 (mean: 0.14) in the ice area, from 0.50 to 0.64 (mean: 0.56) in the snow area. The lower albedo on the glacial surface compared with that of clean bare ice or snow surface suggests that the albedo was significantly reduced by the surface dust on this glacier. Results suggest that the mineral and organic dust on the glacial surface substantially accounts for the recent shrinkage of the glacier. DOI: 10.1657/1523-0430(07-094)[TAKEUCHI]2.0.CO;2 accumulation area, and can be visibly observed in ice cores or Introduction snow pits (e.g. Han et al., 2006; Li et al., 2006; Wake et al., 1994). Surface dust on glaciers can significantly affect albedo on the Recent studies have revealed that surface dust is derived not glacial surface (e.g. Brock et al., 2000; Cutler and Munro, 1996). only from wind-blown desert dust, but also from biological activity Surface materials usually consist of wind-blown dust particles, on the glacial surface, where communities of snow algae, rock from the surrounding valley walls, glacial till, and/or organic microfauna, insects, and bacteria thrive. These organisms are matter produced by glacial organisms. These contaminants in specialized taxa that have adapted to extremely cold environments snow and ice can reduce surface albedo and accelerate the melting (e.g. Hoham and Duval, 2001; Kohshima, 1987). Organic matter of snow and ice. For example, the drastic decrease from 0.8 to 0.5 derived from such organisms forms small spherical granules on the in albedo due to a strong dust storm was observed on the surface glacial ice (e.g. Takeuchi et al., 2001a). Such biogenic surface dust is of a Tibetan glacier (Fujita, 2007). Its impact on glacial runoff has known as cryoconite, and exerts a significant impact on the surface been estimated as a 29% increase over the control runoff without albedo of some glaciers (e.g. Takeuchi et al., 2005; Takeuchi et al., the dust deposition (Fujita, 2007). Recent observational records 2001a; Kohshima et al., 1993). However, the biological element of have shown a substantial thinning and terminus retreat of glaciers surface dust has not been thoroughly studied. in many parts of the world (e.g. Meier et al, 2007; Oerlemans, Uru ¨ mqi Glacier No. 1, located in the Tien Shan Mountains in 2005). Glacial shrinkage is generally considered to result from northwest China, is a glacier in Asia that has been monitored for climate change such as global warming, but also possibly from the more than 40 years and is among those glaciers listed as actively variations in surface dust. Therefore, the characteristics and receding by the World Glacier Monitoring Service (e.g. Ye et al., quantity of surface dust constitute one of the most important 2005). The reports have shown that this glacier is currently parameters needed to determine the mass balance of glaciers. receding rapidly, so it is important to understand the process of On Asian glaciers, wind-blown desert dust is one of major glacial shrinkage. Although much research, including studies of components of surface contamination. Significant amounts of mass balance, ice cores, and snow chemistry, has been carried out wind-blown desert dust are deposited on glaciers in western China on the glacier (e.g. Li et al., 2006; Lee et al., 2003; Wake et al., because the glaciers are surrounded by arid areas encompassing 1992), the characteristics of surface dust and effects of surface dust vast deserts such as the Taklimakan, Junggar, and Gobi (e.g. on the mass balance of this glacier have not yet been studied. Wake et al., 1994). In this region, dust storms usually occur in This paper aims to describe the quantity and characteristics of spring and deposit enormous amounts of fine desert particles on surface dust on the Uru ¨ mqi Glacier No. 1. Dust collected from the glacial surface. Such annual deposits form dust layers in the various parts of the glacier in August 2006 was analyzed, and its 744 / ARCTIC,ANTARCTIC, AND ALPINE RESEARCH 2008 Regents of the University of Colorado 1523-0430/08 $7.00 ¨ FIGURE 2. Pictures of Uru ¨ mqi Glacier No. 1. (top) East (left) and west (right) branches of the Uru ¨ mqi Glacier No. 1 from a moraine (2 August 2006). (bottom) East branch of the glacier. Monitoring Service of the International Commission on Snow and Ice. According to those records, the glacier has retreated continu- ously from 1962 to 2003, with the overall decrease during that period amounting to 20% of the glacier volume (Ye et al., 2005). The recent mean equilibrium line altitude was measured as 4110 m a.s.l. (1997– 2003; Ye et al., 2005). Because the glacier is located in the headwaters ¨ ¨ of the Uru ¨ mqi River that flows into Uru ¨ mqi, which is the largest city in this region with a population of approximately 1.6 million, the FIGURE 1. Geographical location (a) and map (b) of the Uru ¨ mqi glacial shrinkage is causing great concern over its impact on water Glacier No. 1 in the Tien Shan Mountains, China. Study sites are resources (Ye et al., 2005). shown on the map. Field work was carried out from 2 to 5 August 2006. Sample collections and spectral albedo measurements were done at 6 sites characteristics were compared with those from other glaciers on the east branch (SE1–SE6) and at 2 on the west branch (SW1 across the world. The spatial variations in surface albedo were and SW2) (Fig. 1). The sites chosen were visibly representative of measured on the glacier, and the effects of surface dust on the the surface conditions around each site in terms of their surface surface albedo are also discussed. roughness and the amounts of rock debris. Moreover, these sites were selected because of their safety and easy accessibility. The snow line in our study period (early August) was approximately Study Site and Methods 4000 m a.s.l., and was located between sites SE4 and SE5 on the The Tien Shan Mountains are one of the major mountain east branch, and SW1 and SW2 on the west branch (Fig. 1). systems in central Asia with peaks rising about 4000–6000 m a.s.l. In order to quantify the amount of dust on the glacial surface The Uru ¨ mqi Glacier No. 1 (43u069N, 86u489E) is located on the and its organic-matter content, ice and snow on the surface layers eastern side of the Tien Shan Mountains in the Xinjyang Uygur were collected with a stainless-steel scoop (approximately 15 cm 3 autonomous region of China. The total area of the glacier is 15 cm in area and 1–3 cm in depth) from 5 sites in the bare ice area approximately 1.73 km . It lies between 3740 and 4486 m a.s.l., faces (SE1–SE4, and SW1) and 3 in the snow area (SE5, SE6, and SW2). northwest, and consists of two branches (the east and west branches), Five samples were collected from randomly selected surfaces at which became separated in 1994 due to glacial shrinkage (Figs. 1 and each study site. Collection areas on the surface were measured to 2). Mass balance of the glacier has been monitored since 1959, and calculate the amount of dust per unit area. To fix biological the resulting records have been published in annual reports of the activity, the collected samples were melted and preserved as a 3% Tianshan Glacier Station, as well as compiled by the World Glacier formalin solution in clean 30-mL polyethylene bottles. All samples N. TAKEUCHI AND Z. LI / 745 FIGURE 4. Altitudinal distribution of amounts of surface dust on the Uru ¨ mqi Glacier No. 1. Error bars indicate standard deviation. Results AMOUNTS OF DUST ON THE GLACIER SURFACE Most of the glacial surface of the ice area was covered with brown dust (Fig. 3). The amounts of dust on the bare ice surface FIGURE 3. The bare ice surface on the Uru ¨ mqi Glacier No. 1. 22 22 ranged from 86 to 1113 g m (mean: 335 g m , standard (top) Glacial ice surface covered with brown dust. (site SE3 on 2 deviation [SD] 5 211) in dry weight. The altitudinal profile of August 2006). (bottom) Surface dust on the ice. (site SE3 on 2 such amounts showed that those at the higher elevation sites (SE4 August 2006). and SW1) were greater than those at the other sites except for the snow area (431–480 versus 238–267 g m ; Fig. 4); however, the difference was not statistically significant (one-way ANOVA test, were transported for analysis to a laboratory of Chiba University, F 5 1.37, P 5 0.288). Dust was also deposited at the bottom of Japan. The samples were dried (60uC, 24 hours) in pre-weighed cryoconite holes, relatively higher numbers of which were crucibles. The amount of dust per unit area of the glacier was observed at site S3, in contrast to only a few at the other sites. obtained based on measurements of the dry weight and the Dust amounts in the snow area were much smaller than in the ice sampling area. The dried samples were then combusted for 22 22 area, ranging from 4.0 to 9.8 g m (mean: 6.2 g m ,SD 5 1.5). 3 hours at 500uC in an electric furnace, and weighed again. The The surface dust in the ice area contained levels of organic amount of organic matter was calculated from the difference in matter ranging from 7.3 to 11.9% (mean: 9.4%,SD 5 1.6) in dry weight between the dried and combusted samples. This method is weight (Fig. 5). The percentage of organic matter for specific sites slightly modified from Dean (1974). After combustion, only was highest at site SE2 (11.5 6 0.5%, mean 6 SD), and gradually mineral particles remained. In order to investigate the composition diminished down to site SE4 (8.0 6 0.6%) as the elevation of the surface dust, other samples of surface ice/snow were increased. The organic-matter content in the snow-surface dust collected and examined with optical microscopes (Leica MZ125, was lower than that on the ice surface, ranging from 3.5 to 5.9% and Nikon E600). (mean: 5.1%,SD 5 0.59). Spectral reflectances in the visible to near-infrared wave- The amount of organic matter per unit area on the glacial length range (350–1050 nm) were measured on the glacial surface 22 22 surface ranged from 7.4 to 82.3 g m (mean: 30.2 g m ,SD 5 with a portable spectroradiometer (MS-720, Eiko Seiki, Japan). 15.6) on the ice surface, and from 0.18 to 0.42 (mean: 0.31 g m , Measurements were taken using the sensor at a height of SD 5 0.07) on the snow surface (Fig. 6). The amount on the ice approximately 20 cm above the surface of the ice or snow with surface was relatively lower at the lowest site (20.5 6 12.6 g m , the instrument in the nadir-viewing position. Measurements SE1) and higher at sites SE4 and SW1 (37.8 6 27.2 and 35.0 6 made at this height provided a spot 8.9 cm in diameter on the 8.1 g m , respectively). snow or ice surface. The reflectances were obtained by dividing the surface radiances by the radiance acquired from a white reference panel that is nearly 100% reflective and diffuse. COMPOSITION OF SURFACE DUST Measurements of the white panel were made immediately before Microscopic study of the surface dust revealed mineral and after each surface measurement. Spectral reflectances were measured at five surfaces randomly selected at each site. The particles, amorphous organic matter, and living cyanobacteria. mean of the five surface measurements at a given site constitutes The proportion of the components, when observed by microscopy, the reflectance at that site. clearly differed between the dust in snow and ice areas (Fig. 7). 746 / ARCTIC,ANTARCTIC, AND ALPINE RESEARCH FIGURE 5. Altitudinal distribution of percentages of organic matter in surface dust (dry weight) on the Uru ¨ mqi Glacier No. 1. Error bars indicate standard deviation. Brown organic granules were the main component in dust from the ice area (SE1–SE4, SW1), whereas mineral particles predom- inated in the snow area (SE5, SE6, and SW2) (Fig. 7). The brown granules are spherical and contain an abundance of filamentous cyanobacteria and mineral particles. The size of the organic granules ranged from 0.48 to 4.1 mm (mean: 1.4 mm, SD 5 0.47). Observation with a fluorescence microscope revealed at least three FIGURE 7. Microscopic view of surface dust on the Uru ¨ mqi taxa of filamentous cyanobacteria with autofluorescence densely Glacier No. 1. (top) Dust (cryoconite) on the ice surface collected covering the surface of the granules. The morphological charac- from site SE2. Dust consisted mainly of small brown granules teristics of the three taxa were: (1) 2.9 6 0.27 mm (mean 6 SD) in containing cyanobacteria and organic matter. (bottom) The dust cell diameter with a sheath, (2) 1.0 6 0.12 mm in cell diameter with collected on the snow surface from SE5 consisted mainly of mineral particles. a sheath, and (3) 1.0 6 0.11 mm in cell diameter without a sheath. The mineral particles in the dust were brown, white, or transparent, and were microscopically observed to range from 1.3 to 98 mm (mean: 15.2 mm, SD 5 8.6) in diameter. The minerals appear to be quartz, feldspar, mica, calcite, and clay minerals, although more detailed studies are required. The dust on the snow surface mainly consisted of mineral particles, but also contained spherical unicellular green algae (Chlorophyta). The algal cells were red or green in color, and ranged 8.8 6 3.5 mm (mean 6 SD) in size. The algae were relatively more abundant at site SE5 than at site SE6. SPECTRAL REFLECTANCE OF THE GLACIER SURFACE Spectral reflectance on the glacial surface varied among the study sites (Fig. 8). The reflectance in the measured wavelength range (350–1050 nm) varied from 0.076 to 0.221 on the ice surface (SE1–SE4), and was significantly lower than on the snow surface, which varied from 0.341 to 0.661. In the ice surface spectra, the reflectance in the range between 550 and 850 nm was relatively FIGURE 6. Altitudinal distribution of amounts of organic matter higher than in other ranges. A small absorption (depression in the on the surface of the Uru ¨ mqi Glacier No. 1. Error bars indicate spectrum) was apparent at 680 nm in the ice-surface spectra. The standard deviation. snow-surface spectra showed that albedo increased as wavelength N. TAKEUCHI AND Z. LI / 747 FIGURE 8. Spectral albedos in visible wavelength region on the FIGURE 9. Altitudinal profile of integral albedos of visible surface of the Uru ¨ mqi Glacier No. 1 (the east branch). An arrow wavelength region on the surface of the Uru ¨ mqi Glacier No. 1 (the shows absorption feature at 680 nm due to chlorophyll a in the east branch). surface dust. Error bars indicate standard deviation. increased from 350 to 600 nm, held steady between 0.6 and 0.7 The composition of surface dust suggests that dust in the from 600 to 850 nm, and then decreased from 850 to 1050 nm. snow area mainly consisted of deposits of wind-blown mineral The integrated albedos in the measured wavelength range desert dust, while that in the ice area was mostly composed of varied from 0.093 to 0.236 (mean: 0.143) in the ice area, and from cryoconite granules formed by microbial activity on the glacier. As 0.496 to 0.638 (mean: 0.560) in the snow area (Fig. 9). The albedo previous studies have shown, significant amounts of desert dust at the lowest site (SE1) was the highest in the ice area, while that at can be deposited on the northern slopes of the Tien Shan the middle site (SE3) was the lowest. In the snow area, the albedo Mountains from surrounding deserts such as the Junggar (Sun, at the lower site was lower than that at the higher site (0.531 at 2002). Since microscopy confirmed that dust on the snow surface SE5 versus 0.588 at SE6). consisted mainly of fine mineral particles (Fig. 7), it appeared to be mostly wind-blown desert dust. On other glaciers, for example, some in Alaska and Altai, red colored snow algae account for the Discussion reduction in surface albedo in the snow area (e.g. Takeuchi, 2001d; Takeuchi et al., 2006a, 2006b). Microscopy revealed red algal cells Our results indicate that surface dust significantly reduced the in the dust on the snow of Uru ¨ mqi Glacier No. 1. These are surface albedo of Uru ¨ mqi Glacier No. 1. In the ice area, the probably Chloromonas sp., which is a common genus of snow spectral reflectances measured on the surface showed that the algae (Chlorophyta) with red pigments. However, since the reflectances in the visible wavelength range (350–800 nm) were amount of algae appeared to be much less than that of mineral generally low, but slightly higher in the range between 550 and particles, their effect on surface albedo is likely negligible. Were 850 nm. They exhibit the typical spectral curves of a dirty glacial the algae to affect the surface albedo significantly, the absorption ice surface (e.g. Zeng et al., 1984). The higher reflectance between feature of chlorophyll a would be apparent at a wavelength of 550 and 850 nm corresponded to the optical characteristics of 680 nm (e.g. Takeuchi et al., 2006a). However, there was no such glacial surface dust on Chinese glaciers (Takeuchi, 2002b). The absorption at 680 nm in the snow surface spectra, confirming the mean integrated albedo of the ice surface on the glacier was 0.143, insignificant contribution of the algal cells to surface albedo which is lower than that of a clean, bare ice surface, which is reduction. generally 0.34–0.51 (Paterson, 1994). In western China, it has been In contrast to the snow area, surface dust in the ice area reported to be 0.38 (0.34 to 0.42) on glaciers (Bai and Yu, 1985). contained high levels of organic matter and cyanobacteria. The The difference between the albedo of bare ice and the measured mass fraction of organic matter in dust on the ice surface (9.4%) glacial albedo is 0.24, which equals the approximate effect of surface dust on this glacier. was considerably higher than that on the snow surface (5.1%). Microscopy showed that the dust consisted mainly of small brown The reduction in albedo by surface dust was also significant in granules that were not observed on the snow surface (Fig. 7). In the snow area. The spectral reflectance of clean snow or firn addition, their size, composition, and structure resemble those of surface in the visible wavelength usually ranges from 0.60 to 0.95 cryoconite granules, already reported on a Himalayan glacier, and continuously diminishes as wavelength increases (e.g. Zeng et growing as an algal mat on the glacial surface (Takeuchi et al., al., 1984). On the Uru ¨ mqi Glacier No. 1, the spectral albedos on 2001a). Thus, these granules are likely to be the products of two sites (SE5 and SE6) in the snow area showed that the albedo was generally lower than that of clean snow, and was particularly biological activity on the glacial surface. Although the mass lower in the range between 350 and 550 nm. This curve indicates fraction of organic matter in the dust was only 9.4% in dry weight, that the snow albedo was reduced by dust on the surface. microscopy shows that the organic matter was comparable to the 748 / ARCTIC,ANTARCTIC, AND ALPINE RESEARCH abundant wind-blown deposits of desert dust, while those of organic components may be the result of intensive biological productivity on the glacial surface. Long-term mass balance measurements of the Uru ¨ mqi Glacier No. 1 have shown a negative mass balance from 1958 to 2003 (210,032 mm), which is equivalent to a glacial thinning of 11.1 m (Ye et al., 2005). In particular, mass balance change has been continuous and highly negative in a recent 5-year period (1997–2002). Analysis of the mass balance and climate data suggests that the negative mass balance of the glacier is due to an increase in summer temperatures (Ye et al., 2005). Warmer summer temperatures could increase the frequency of rain instead of snowfall. Snowfall could cover the ablation ice surface, raise its albedo, and thus decrease its melting. However, increase of the frequency of rain could allow the dusty ablation surface to be exposed for a longer time (Fujita and Ageta, 2000). Therefore, the effect of surface dust on glacial melting could drastically increase when summer temperature increases. Thus, an enormous accu- mulation of surface dust probably accounts for the recent accelerated shrinkage of the glacier. Our results show that organic matter contributes significantly to the reduction in surface albedo and may affect ablation of the glacial surface. Previous studies have shown that anthropogenic pollution was a significant factor in altering the chemical FIGURE 10. Comparison of amounts of surface dust and their conditions of snow and ice on this glacier (e.g., Lee et al., 2003). components among various glaciers around the world. Error bars indicate standard deviation. Such chemical alterations of snow and ice may affect the biological community, changing the amount of organic dust, and then possibly altering the glacial surface albedo. Further study is mineral components in terms of particle volume. The smaller mass necessary to improve our understanding of what accounts for fraction of organic matter is likely due to its lower density compared variations in a biological community and to evaluate better the with that of mineral particles. In the ice-surface spectra, an effect of microbial activity on glacial surface albedo. absorption of around 680 nm was apparent, and was presumably due to the chlorophyll a of snow algae and cyanobacteria on the glacial surface (Fig. 8). This indicates that organic components also Acknowledgments exert a major influence on the surface albedo. Although the We wish to thank Wan Feiteng, Zhou Ping, and other staff quantitative contribution of each component to albedo reduction and students of the Cold and Arid Regions Environment and is uncertain, both organic and inorganic components are likely to be Engineering Research Institute of the Chinese Academy of Science effective in reducing the surface albedo on this glacier. in Lanzhou, China, for their valuable logistical support of the field The amount of total (organic plus inorganic) surface dust on work. This study was financially supported by a Grant-in-Aid for the ice surface of the Uru ¨ mqi Glacier No. 1 is roughly equivalent Young Scientists (A, No. 18681005) and a Grant-in-Aid for to those on other glaciers in China and the Himalayas, but is Scientific Research (B, No. 19310020) of the Japan Society for the markedly greater than on glaciers in other parts of the world. Promotion of Science (JSPS) and also partly by the Ili Project According to previous studies, the average amount on the July 1st funded by the Research Institute for Humanity and Nature, Glacier in the Qilian Mountains, China, was 292 g m (Takeuchi Japan. We also thank two reviewers (Todd Hinkley and et al., 2005). The amount of dust recorded on the Yala Glacier in anonymous) and an associate editor, Dan Muhs, for helpful suggestions that very much improved the manuscript. the Himalayas was 225 g m (Takeuchi et al., 2000). These amounts are roughly comparable to that on the Uru ¨ mqi Glacier No. 1. 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The amount of mineral dust on the reflectivity during the ablation period on Peyto Glacier, Alberta, Uru ¨ mqi Glacier No. 1 was approximately 15 times higher than the Canada. Journal of Glaciology, 42(141): 333–340. mean of that on the Patagonian, Alaskan, and Canadian Arctic Dean, W. E., 1974: Determination of carbonate and organic glaciers (297 versus 20.3 g m ), while the amount of organic matter in calcareous sediments and sedimentary rocks by loss on matter was approximately 45 times higher (30 versus 0.67 g m ). ignition; comparison with other methods. Journal of Sedimen- The amounts of both mineral dust and organic matter on Uru ¨ mqi tary Research, 44: 242–248. Glacier No. 1 are also higher when compared with other Asian Fujita, K., 2007: Effect of dust event timing on glacier runoff; glaciers (Fig. 10). The higher levels of inorganic components on sensitivity analysis for a Tibetan glacier. 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Characteristics of Surface Dust on Ürümqi Glacier No. 1 in the Tien Shan Mountains, China

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Taylor & Francis
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© 2008 Arctic, Antarctic, and Alpine Research
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1938-4246
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1523-0430
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10.1657/1523-0430(07-094)[TAKEUCHI]2.0.CO;2
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Abstract

Zhongqin Li{ Monitoring studies show that many mountain glaciers worldwide are decreasing in mass. An important component of the process of ice mass loss is the effect of dust on *Corresponding author: Department of albedo and its effect on glacier mass balance. The characteristics of surface dust were Earth Sciences, Graduate School of Science, Chiba University, 1-33, investigated in August 2006 on the Uru ¨ mqi Glacier No. 1 in the Tien Shan Yayoicho, Inage-ku, Chiba-city, Chiba Mountains, China. The bare ice surface of the glacier was mostly covered by brown 263-8522, Japan dust. The amounts of surface dust on the ice surface (dry weight) ranged from86to ntakeuch@faculty.chiba-u.jp 22 22 1113 g m (mean: 335 g m , standard deviation: 5 211), which is within the {Laboratory of Cryosphere and normal range for Asian glaciers, but significantly greater than those on glaciers in Environment/Tien Shan Glaciological Station, Cold and Arid Regions other regions such as Alaska, Patagonia, and the Canadian Arctic. An analysis of Environmental and Engineering organic matter and microscopy of the surface dust revealed that the dust contained Research Institute, Chinese Academy of high levels of organic matter, including living cyanobacteria. This suggests that it is Sciences, 320 Donggang West Road, comprised not only of deposits of wind-blown desert dust, but is also a product of Lanzhou 730000, China microbial activity on the glacier itself. Spectral albedo of the glacial surface showed lizq@lzb.ac.cn spectrum curves typical of those of snow and ice contaminated with dust. The integrated surface albedo ranged from 0.09 to 0.24 (mean: 0.14) in the ice area, from 0.50 to 0.64 (mean: 0.56) in the snow area. The lower albedo on the glacial surface compared with that of clean bare ice or snow surface suggests that the albedo was significantly reduced by the surface dust on this glacier. Results suggest that the mineral and organic dust on the glacial surface substantially accounts for the recent shrinkage of the glacier. DOI: 10.1657/1523-0430(07-094)[TAKEUCHI]2.0.CO;2 accumulation area, and can be visibly observed in ice cores or Introduction snow pits (e.g. Han et al., 2006; Li et al., 2006; Wake et al., 1994). Surface dust on glaciers can significantly affect albedo on the Recent studies have revealed that surface dust is derived not glacial surface (e.g. Brock et al., 2000; Cutler and Munro, 1996). only from wind-blown desert dust, but also from biological activity Surface materials usually consist of wind-blown dust particles, on the glacial surface, where communities of snow algae, rock from the surrounding valley walls, glacial till, and/or organic microfauna, insects, and bacteria thrive. These organisms are matter produced by glacial organisms. These contaminants in specialized taxa that have adapted to extremely cold environments snow and ice can reduce surface albedo and accelerate the melting (e.g. Hoham and Duval, 2001; Kohshima, 1987). Organic matter of snow and ice. For example, the drastic decrease from 0.8 to 0.5 derived from such organisms forms small spherical granules on the in albedo due to a strong dust storm was observed on the surface glacial ice (e.g. Takeuchi et al., 2001a). Such biogenic surface dust is of a Tibetan glacier (Fujita, 2007). Its impact on glacial runoff has known as cryoconite, and exerts a significant impact on the surface been estimated as a 29% increase over the control runoff without albedo of some glaciers (e.g. Takeuchi et al., 2005; Takeuchi et al., the dust deposition (Fujita, 2007). Recent observational records 2001a; Kohshima et al., 1993). However, the biological element of have shown a substantial thinning and terminus retreat of glaciers surface dust has not been thoroughly studied. in many parts of the world (e.g. Meier et al, 2007; Oerlemans, Uru ¨ mqi Glacier No. 1, located in the Tien Shan Mountains in 2005). Glacial shrinkage is generally considered to result from northwest China, is a glacier in Asia that has been monitored for climate change such as global warming, but also possibly from the more than 40 years and is among those glaciers listed as actively variations in surface dust. Therefore, the characteristics and receding by the World Glacier Monitoring Service (e.g. Ye et al., quantity of surface dust constitute one of the most important 2005). The reports have shown that this glacier is currently parameters needed to determine the mass balance of glaciers. receding rapidly, so it is important to understand the process of On Asian glaciers, wind-blown desert dust is one of major glacial shrinkage. Although much research, including studies of components of surface contamination. Significant amounts of mass balance, ice cores, and snow chemistry, has been carried out wind-blown desert dust are deposited on glaciers in western China on the glacier (e.g. Li et al., 2006; Lee et al., 2003; Wake et al., because the glaciers are surrounded by arid areas encompassing 1992), the characteristics of surface dust and effects of surface dust vast deserts such as the Taklimakan, Junggar, and Gobi (e.g. on the mass balance of this glacier have not yet been studied. Wake et al., 1994). In this region, dust storms usually occur in This paper aims to describe the quantity and characteristics of spring and deposit enormous amounts of fine desert particles on surface dust on the Uru ¨ mqi Glacier No. 1. Dust collected from the glacial surface. Such annual deposits form dust layers in the various parts of the glacier in August 2006 was analyzed, and its 744 / ARCTIC,ANTARCTIC, AND ALPINE RESEARCH 2008 Regents of the University of Colorado 1523-0430/08 $7.00 ¨ FIGURE 2. Pictures of Uru ¨ mqi Glacier No. 1. (top) East (left) and west (right) branches of the Uru ¨ mqi Glacier No. 1 from a moraine (2 August 2006). (bottom) East branch of the glacier. Monitoring Service of the International Commission on Snow and Ice. According to those records, the glacier has retreated continu- ously from 1962 to 2003, with the overall decrease during that period amounting to 20% of the glacier volume (Ye et al., 2005). The recent mean equilibrium line altitude was measured as 4110 m a.s.l. (1997– 2003; Ye et al., 2005). Because the glacier is located in the headwaters ¨ ¨ of the Uru ¨ mqi River that flows into Uru ¨ mqi, which is the largest city in this region with a population of approximately 1.6 million, the FIGURE 1. Geographical location (a) and map (b) of the Uru ¨ mqi glacial shrinkage is causing great concern over its impact on water Glacier No. 1 in the Tien Shan Mountains, China. Study sites are resources (Ye et al., 2005). shown on the map. Field work was carried out from 2 to 5 August 2006. Sample collections and spectral albedo measurements were done at 6 sites characteristics were compared with those from other glaciers on the east branch (SE1–SE6) and at 2 on the west branch (SW1 across the world. The spatial variations in surface albedo were and SW2) (Fig. 1). The sites chosen were visibly representative of measured on the glacier, and the effects of surface dust on the the surface conditions around each site in terms of their surface surface albedo are also discussed. roughness and the amounts of rock debris. Moreover, these sites were selected because of their safety and easy accessibility. The snow line in our study period (early August) was approximately Study Site and Methods 4000 m a.s.l., and was located between sites SE4 and SE5 on the The Tien Shan Mountains are one of the major mountain east branch, and SW1 and SW2 on the west branch (Fig. 1). systems in central Asia with peaks rising about 4000–6000 m a.s.l. In order to quantify the amount of dust on the glacial surface The Uru ¨ mqi Glacier No. 1 (43u069N, 86u489E) is located on the and its organic-matter content, ice and snow on the surface layers eastern side of the Tien Shan Mountains in the Xinjyang Uygur were collected with a stainless-steel scoop (approximately 15 cm 3 autonomous region of China. The total area of the glacier is 15 cm in area and 1–3 cm in depth) from 5 sites in the bare ice area approximately 1.73 km . It lies between 3740 and 4486 m a.s.l., faces (SE1–SE4, and SW1) and 3 in the snow area (SE5, SE6, and SW2). northwest, and consists of two branches (the east and west branches), Five samples were collected from randomly selected surfaces at which became separated in 1994 due to glacial shrinkage (Figs. 1 and each study site. Collection areas on the surface were measured to 2). Mass balance of the glacier has been monitored since 1959, and calculate the amount of dust per unit area. To fix biological the resulting records have been published in annual reports of the activity, the collected samples were melted and preserved as a 3% Tianshan Glacier Station, as well as compiled by the World Glacier formalin solution in clean 30-mL polyethylene bottles. All samples N. TAKEUCHI AND Z. LI / 745 FIGURE 4. Altitudinal distribution of amounts of surface dust on the Uru ¨ mqi Glacier No. 1. Error bars indicate standard deviation. Results AMOUNTS OF DUST ON THE GLACIER SURFACE Most of the glacial surface of the ice area was covered with brown dust (Fig. 3). The amounts of dust on the bare ice surface FIGURE 3. The bare ice surface on the Uru ¨ mqi Glacier No. 1. 22 22 ranged from 86 to 1113 g m (mean: 335 g m , standard (top) Glacial ice surface covered with brown dust. (site SE3 on 2 deviation [SD] 5 211) in dry weight. The altitudinal profile of August 2006). (bottom) Surface dust on the ice. (site SE3 on 2 such amounts showed that those at the higher elevation sites (SE4 August 2006). and SW1) were greater than those at the other sites except for the snow area (431–480 versus 238–267 g m ; Fig. 4); however, the difference was not statistically significant (one-way ANOVA test, were transported for analysis to a laboratory of Chiba University, F 5 1.37, P 5 0.288). Dust was also deposited at the bottom of Japan. The samples were dried (60uC, 24 hours) in pre-weighed cryoconite holes, relatively higher numbers of which were crucibles. The amount of dust per unit area of the glacier was observed at site S3, in contrast to only a few at the other sites. obtained based on measurements of the dry weight and the Dust amounts in the snow area were much smaller than in the ice sampling area. The dried samples were then combusted for 22 22 area, ranging from 4.0 to 9.8 g m (mean: 6.2 g m ,SD 5 1.5). 3 hours at 500uC in an electric furnace, and weighed again. The The surface dust in the ice area contained levels of organic amount of organic matter was calculated from the difference in matter ranging from 7.3 to 11.9% (mean: 9.4%,SD 5 1.6) in dry weight between the dried and combusted samples. This method is weight (Fig. 5). The percentage of organic matter for specific sites slightly modified from Dean (1974). After combustion, only was highest at site SE2 (11.5 6 0.5%, mean 6 SD), and gradually mineral particles remained. In order to investigate the composition diminished down to site SE4 (8.0 6 0.6%) as the elevation of the surface dust, other samples of surface ice/snow were increased. The organic-matter content in the snow-surface dust collected and examined with optical microscopes (Leica MZ125, was lower than that on the ice surface, ranging from 3.5 to 5.9% and Nikon E600). (mean: 5.1%,SD 5 0.59). Spectral reflectances in the visible to near-infrared wave- The amount of organic matter per unit area on the glacial length range (350–1050 nm) were measured on the glacial surface 22 22 surface ranged from 7.4 to 82.3 g m (mean: 30.2 g m ,SD 5 with a portable spectroradiometer (MS-720, Eiko Seiki, Japan). 15.6) on the ice surface, and from 0.18 to 0.42 (mean: 0.31 g m , Measurements were taken using the sensor at a height of SD 5 0.07) on the snow surface (Fig. 6). The amount on the ice approximately 20 cm above the surface of the ice or snow with surface was relatively lower at the lowest site (20.5 6 12.6 g m , the instrument in the nadir-viewing position. Measurements SE1) and higher at sites SE4 and SW1 (37.8 6 27.2 and 35.0 6 made at this height provided a spot 8.9 cm in diameter on the 8.1 g m , respectively). snow or ice surface. The reflectances were obtained by dividing the surface radiances by the radiance acquired from a white reference panel that is nearly 100% reflective and diffuse. COMPOSITION OF SURFACE DUST Measurements of the white panel were made immediately before Microscopic study of the surface dust revealed mineral and after each surface measurement. Spectral reflectances were measured at five surfaces randomly selected at each site. The particles, amorphous organic matter, and living cyanobacteria. mean of the five surface measurements at a given site constitutes The proportion of the components, when observed by microscopy, the reflectance at that site. clearly differed between the dust in snow and ice areas (Fig. 7). 746 / ARCTIC,ANTARCTIC, AND ALPINE RESEARCH FIGURE 5. Altitudinal distribution of percentages of organic matter in surface dust (dry weight) on the Uru ¨ mqi Glacier No. 1. Error bars indicate standard deviation. Brown organic granules were the main component in dust from the ice area (SE1–SE4, SW1), whereas mineral particles predom- inated in the snow area (SE5, SE6, and SW2) (Fig. 7). The brown granules are spherical and contain an abundance of filamentous cyanobacteria and mineral particles. The size of the organic granules ranged from 0.48 to 4.1 mm (mean: 1.4 mm, SD 5 0.47). Observation with a fluorescence microscope revealed at least three FIGURE 7. Microscopic view of surface dust on the Uru ¨ mqi taxa of filamentous cyanobacteria with autofluorescence densely Glacier No. 1. (top) Dust (cryoconite) on the ice surface collected covering the surface of the granules. The morphological charac- from site SE2. Dust consisted mainly of small brown granules teristics of the three taxa were: (1) 2.9 6 0.27 mm (mean 6 SD) in containing cyanobacteria and organic matter. (bottom) The dust cell diameter with a sheath, (2) 1.0 6 0.12 mm in cell diameter with collected on the snow surface from SE5 consisted mainly of mineral particles. a sheath, and (3) 1.0 6 0.11 mm in cell diameter without a sheath. The mineral particles in the dust were brown, white, or transparent, and were microscopically observed to range from 1.3 to 98 mm (mean: 15.2 mm, SD 5 8.6) in diameter. The minerals appear to be quartz, feldspar, mica, calcite, and clay minerals, although more detailed studies are required. The dust on the snow surface mainly consisted of mineral particles, but also contained spherical unicellular green algae (Chlorophyta). The algal cells were red or green in color, and ranged 8.8 6 3.5 mm (mean 6 SD) in size. The algae were relatively more abundant at site SE5 than at site SE6. SPECTRAL REFLECTANCE OF THE GLACIER SURFACE Spectral reflectance on the glacial surface varied among the study sites (Fig. 8). The reflectance in the measured wavelength range (350–1050 nm) varied from 0.076 to 0.221 on the ice surface (SE1–SE4), and was significantly lower than on the snow surface, which varied from 0.341 to 0.661. In the ice surface spectra, the reflectance in the range between 550 and 850 nm was relatively FIGURE 6. Altitudinal distribution of amounts of organic matter higher than in other ranges. A small absorption (depression in the on the surface of the Uru ¨ mqi Glacier No. 1. Error bars indicate spectrum) was apparent at 680 nm in the ice-surface spectra. The standard deviation. snow-surface spectra showed that albedo increased as wavelength N. TAKEUCHI AND Z. LI / 747 FIGURE 8. Spectral albedos in visible wavelength region on the FIGURE 9. Altitudinal profile of integral albedos of visible surface of the Uru ¨ mqi Glacier No. 1 (the east branch). An arrow wavelength region on the surface of the Uru ¨ mqi Glacier No. 1 (the shows absorption feature at 680 nm due to chlorophyll a in the east branch). surface dust. Error bars indicate standard deviation. increased from 350 to 600 nm, held steady between 0.6 and 0.7 The composition of surface dust suggests that dust in the from 600 to 850 nm, and then decreased from 850 to 1050 nm. snow area mainly consisted of deposits of wind-blown mineral The integrated albedos in the measured wavelength range desert dust, while that in the ice area was mostly composed of varied from 0.093 to 0.236 (mean: 0.143) in the ice area, and from cryoconite granules formed by microbial activity on the glacier. As 0.496 to 0.638 (mean: 0.560) in the snow area (Fig. 9). The albedo previous studies have shown, significant amounts of desert dust at the lowest site (SE1) was the highest in the ice area, while that at can be deposited on the northern slopes of the Tien Shan the middle site (SE3) was the lowest. In the snow area, the albedo Mountains from surrounding deserts such as the Junggar (Sun, at the lower site was lower than that at the higher site (0.531 at 2002). Since microscopy confirmed that dust on the snow surface SE5 versus 0.588 at SE6). consisted mainly of fine mineral particles (Fig. 7), it appeared to be mostly wind-blown desert dust. On other glaciers, for example, some in Alaska and Altai, red colored snow algae account for the Discussion reduction in surface albedo in the snow area (e.g. Takeuchi, 2001d; Takeuchi et al., 2006a, 2006b). Microscopy revealed red algal cells Our results indicate that surface dust significantly reduced the in the dust on the snow of Uru ¨ mqi Glacier No. 1. These are surface albedo of Uru ¨ mqi Glacier No. 1. In the ice area, the probably Chloromonas sp., which is a common genus of snow spectral reflectances measured on the surface showed that the algae (Chlorophyta) with red pigments. However, since the reflectances in the visible wavelength range (350–800 nm) were amount of algae appeared to be much less than that of mineral generally low, but slightly higher in the range between 550 and particles, their effect on surface albedo is likely negligible. Were 850 nm. They exhibit the typical spectral curves of a dirty glacial the algae to affect the surface albedo significantly, the absorption ice surface (e.g. Zeng et al., 1984). The higher reflectance between feature of chlorophyll a would be apparent at a wavelength of 550 and 850 nm corresponded to the optical characteristics of 680 nm (e.g. Takeuchi et al., 2006a). However, there was no such glacial surface dust on Chinese glaciers (Takeuchi, 2002b). The absorption at 680 nm in the snow surface spectra, confirming the mean integrated albedo of the ice surface on the glacier was 0.143, insignificant contribution of the algal cells to surface albedo which is lower than that of a clean, bare ice surface, which is reduction. generally 0.34–0.51 (Paterson, 1994). In western China, it has been In contrast to the snow area, surface dust in the ice area reported to be 0.38 (0.34 to 0.42) on glaciers (Bai and Yu, 1985). contained high levels of organic matter and cyanobacteria. The The difference between the albedo of bare ice and the measured mass fraction of organic matter in dust on the ice surface (9.4%) glacial albedo is 0.24, which equals the approximate effect of surface dust on this glacier. was considerably higher than that on the snow surface (5.1%). Microscopy showed that the dust consisted mainly of small brown The reduction in albedo by surface dust was also significant in granules that were not observed on the snow surface (Fig. 7). In the snow area. The spectral reflectance of clean snow or firn addition, their size, composition, and structure resemble those of surface in the visible wavelength usually ranges from 0.60 to 0.95 cryoconite granules, already reported on a Himalayan glacier, and continuously diminishes as wavelength increases (e.g. Zeng et growing as an algal mat on the glacial surface (Takeuchi et al., al., 1984). On the Uru ¨ mqi Glacier No. 1, the spectral albedos on 2001a). Thus, these granules are likely to be the products of two sites (SE5 and SE6) in the snow area showed that the albedo was generally lower than that of clean snow, and was particularly biological activity on the glacial surface. Although the mass lower in the range between 350 and 550 nm. This curve indicates fraction of organic matter in the dust was only 9.4% in dry weight, that the snow albedo was reduced by dust on the surface. microscopy shows that the organic matter was comparable to the 748 / ARCTIC,ANTARCTIC, AND ALPINE RESEARCH abundant wind-blown deposits of desert dust, while those of organic components may be the result of intensive biological productivity on the glacial surface. Long-term mass balance measurements of the Uru ¨ mqi Glacier No. 1 have shown a negative mass balance from 1958 to 2003 (210,032 mm), which is equivalent to a glacial thinning of 11.1 m (Ye et al., 2005). In particular, mass balance change has been continuous and highly negative in a recent 5-year period (1997–2002). Analysis of the mass balance and climate data suggests that the negative mass balance of the glacier is due to an increase in summer temperatures (Ye et al., 2005). Warmer summer temperatures could increase the frequency of rain instead of snowfall. Snowfall could cover the ablation ice surface, raise its albedo, and thus decrease its melting. However, increase of the frequency of rain could allow the dusty ablation surface to be exposed for a longer time (Fujita and Ageta, 2000). Therefore, the effect of surface dust on glacial melting could drastically increase when summer temperature increases. Thus, an enormous accu- mulation of surface dust probably accounts for the recent accelerated shrinkage of the glacier. Our results show that organic matter contributes significantly to the reduction in surface albedo and may affect ablation of the glacial surface. Previous studies have shown that anthropogenic pollution was a significant factor in altering the chemical FIGURE 10. Comparison of amounts of surface dust and their conditions of snow and ice on this glacier (e.g., Lee et al., 2003). components among various glaciers around the world. Error bars indicate standard deviation. Such chemical alterations of snow and ice may affect the biological community, changing the amount of organic dust, and then possibly altering the glacial surface albedo. Further study is mineral components in terms of particle volume. The smaller mass necessary to improve our understanding of what accounts for fraction of organic matter is likely due to its lower density compared variations in a biological community and to evaluate better the with that of mineral particles. In the ice-surface spectra, an effect of microbial activity on glacial surface albedo. absorption of around 680 nm was apparent, and was presumably due to the chlorophyll a of snow algae and cyanobacteria on the glacial surface (Fig. 8). This indicates that organic components also Acknowledgments exert a major influence on the surface albedo. Although the We wish to thank Wan Feiteng, Zhou Ping, and other staff quantitative contribution of each component to albedo reduction and students of the Cold and Arid Regions Environment and is uncertain, both organic and inorganic components are likely to be Engineering Research Institute of the Chinese Academy of Science effective in reducing the surface albedo on this glacier. in Lanzhou, China, for their valuable logistical support of the field The amount of total (organic plus inorganic) surface dust on work. This study was financially supported by a Grant-in-Aid for the ice surface of the Uru ¨ mqi Glacier No. 1 is roughly equivalent Young Scientists (A, No. 18681005) and a Grant-in-Aid for to those on other glaciers in China and the Himalayas, but is Scientific Research (B, No. 19310020) of the Japan Society for the markedly greater than on glaciers in other parts of the world. Promotion of Science (JSPS) and also partly by the Ili Project According to previous studies, the average amount on the July 1st funded by the Research Institute for Humanity and Nature, Glacier in the Qilian Mountains, China, was 292 g m (Takeuchi Japan. We also thank two reviewers (Todd Hinkley and et al., 2005). The amount of dust recorded on the Yala Glacier in anonymous) and an associate editor, Dan Muhs, for helpful suggestions that very much improved the manuscript. the Himalayas was 225 g m (Takeuchi et al., 2000). These amounts are roughly comparable to that on the Uru ¨ mqi Glacier No. 1. 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Journal

"Arctic, Antartic and Alpine Research"Taylor & Francis

Published: Nov 1, 2008

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