Elemental composition in surface snow from the ultra-high elevation area of Mt. Qomolangma (Everest)

Chinese Science Bulletin

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Elemental composition in surface snow from the ultra-high elevation area of Mt. Qomolangma (Everest)

ZHANG QiangGong1,2, KANG ShiChang1,3†, CONG ZhiYuan1,2, HOU ShuGui3 & LIU YongQin1,2 1 Institute of Tibetan Plateau Research, Chinese Academy of Sciences CAS, Beijing 100085, China; 2 Graduate University of CAS, Beijing 100049, China; 3 State Key Laboratory of Cryospheric Science, CAS, Lanzhou 730000, China

A total of 14 surface snow (0―10 cm) samples were collected along the climbing route (6500―8844 m a.s.l.) on the northern slope of Mt. Qomolangma in May, 2005. Analysis of elemental concentrations in these samples showed that there are no clear trends for element variations with elevation due to re-distribution of surface snow by strong winds during spring. In addition, local crustal aerosol inputs also have an influence on elemental composition of surface snow. Comparison between elemental concentration datasets of 2005 and 1997 indicated that data from 2005 were of higher quality. Elemental concentrations (especially for heavy metals) at Mt. Qomolangma are comparable with polar sites, and far lower than large cities. This indicates that anthropogenic activities and heavy metal pollution have little effect on the Mt. Qomolangma atmospheric environment, which can be representative of the background atmospheric environment.

Mt. Qomolangma, ultra-high elevation, surface snow, elemental concentration

Mt. Qomolangma (Everest), the highest summit in the world, is minimally influenced by the anthropogenic activities and is thus regarded as a representative region of the background global atmospheric environment[1]. Glaciochemical records from snow/ice are natural ar-chives of atmospheric processes, and are therefore used extensively in measuring environmental variation and tracing anthropogenic pollutants. Trace metals recorded in alpine and polar snow/ice are a sensitive proxy in evaluating anthropogenic influences on the atmospheric environment, and are also used to understand atmos-pheric chemistry processes[2―4]. Extensive research has been carried out on Mt. Qomolangma to evaluate spatial and temporal distributions of major ion concentrations and their sources[5―7]. However, trace metal measure-ments have not been extensively made in Mt. Qomo-langma snow/ice samples[8,9], maily due to their ex-tremely low concentrations (usually at level of ng/g to pg/g) and servere weather conditions in this region. Re-ports concerning trace metals in the snow/ice from the

ultra-high elevation and even the summit of Mt. Qomo-langma are rare and to the best of our knowledge, the only available report[9] was provided by the Third Com-prehensive Scientific Expedition Team who made re-search on Mt. Qomolangma in 1975. This team made thorough preliminary observations to understand the chemical composition of snow from this region. How-ever, the reliability of the data is questionable due to the limitation of the sampling equipment and detection techniques at that time.

In May 2005, a total of 14 surface snow (0―10 cm) samples were collected along the climbing route from the advanced base camp to the summit (6500―8844 m Received February 28, 2007; accepted July 30, 2007 doi: 10.1007/s11434-007-0446-z †Corresponding author (email: [email protected]) Supported by the National Natural Science Foundation of China (Grant Nos. 40401054, 90411003 and 40121101), the National Basic Research Program of China (Grant No.2005CB422004), Social Commonweal Research Project of Ministry of Science and Technology of China (Grant No.2005DIA3J106) ,the “Talent Project” and Innovation Project (Grant No.KZCX3-SW-334/339) of CAS, and Dean Founda-tion of CAS

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a.s.l.). In this paper, major elements and trace metals in the surface snow samples are analyzed and their spatial variations and reasons for the variations are discussed.

1 Materials and methods

In May 2005, a comprehensive scientific expedition to Mt. Qomolangma was organized by the Chinese Acad-emy of Sciences (CAS). During the expedition, a total of 14 surface snow (0―10 cm) samples (Figure 1) were collected along the climbing route from the advanced base camp to the summit (6500―8844 m a.s.l.) on the northern slope of Mt. Qomolangma during the period of May 15―20. Among those samples, 9 were from the elevation of 6500―7300 m , with an elevation interval of 100m, the rest were collected at elevations of 7500 m, 8100 m, 8200 m, 8300 m, and 8844.43 m (the summit), respectively. There was no snowfall in the sampling week. All the samples were directly collected by using pre-acid-cleaned high-density polyethylene (HDPE) containers supplied by Nalgene®. Field blanks filled with ultrapure water were opened during sample collec-tion in the field and handled as samples. Extreme care was taken during sample collection in order to avoid potential contamination and the detailed sampling method is the same as that used by Wake et al.[10,11] and

Kang et al.[6]. Samples were kept frozen in the field, during trans-

portation, and in the laboratory until analysis. All the samples were acidified with 1% nitric acid and analyzed for a total of 20 elements, namely, B, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Cu, Zn, As, Se, Mo, Cd, Sb, Cs, and Pb by ICP-MS (Agilent 7500a) at the Institute of At-mospheric Physics, CAS. Most of the elemental concen-trations of blank samples are below the instrument de-tection limit, indicating minimal contamination during sampling and analysis. Evaluation of measured elemen-tal concentrations and detection limits indicated the re-liability of the data. δ 18O was measured using an MAT-253 with precision of 0.5‰ at the Institute of Ti-betan Plateau Research, CAS.

2 Results and discussion

2.1 δ 18O and elemental concentrations

Mt. Qomolangma is located in the southern Tibetan Pla-teau, central Himalaya with its climate being signifi-cantly influenced by the Indian Monsoon. Previous studies[7,12] suggested that δ 18O in precipitation from this area presents a clear “precipitation effect”, namely a negative correlation between δ 18O and precipitation amount[13]. Zhang et al.[7] investigated δ 18O and major

Figure 1 Map showing the sampling locations.

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ions in fresh snow from Mt. Qomolangma and suggested that precipitation mainly occurs in the period of early June to September. The 14 samples in this study were collected in the middle of May. The mean δ 18O of −16.73‰ suggested that the elemental concentrations are most likely representative of the spring atmospheric environment in this region. Since less precipitation events occurred in spring and there was no snowfall during the sampling week, elemental composition is mainly contributed by aerosol dry deposition.

Elemental concentration variations with the increas-ing elevation are presented in Figure 2, Cr, Co, Cd, Cs, and Pb are not shown because their concentrations are extremely low and in most samples their concentrations

are lower than the detection limits. Ca, Na, K, Mg, and Fe have higher concentrations, with Ca concentrations being the highest, reaching 80 μg/g at the elevation around 6500 m. Concentrations of trace metals are typi-cally in the order of several ng/g. Previous studies sug-gested that high concentrations of soluble components of the elements (e.g. Ca2+, Na+, K+, Mg2+) in spring in the Mt. Qomolangma region were mainly caused by spring dust storms over Asia[5,6]. High concentrations of Ca and other crustal elements are mainly caused by the influ-ence of crustal aerosols from prevalent spring dust storms over the Tibetan Plateau[6,14,15] or South/Central Asia[5,10]. The low concentrations of elements which may come from anthropogenic sources (e.g. Cr, Co, Cd,

Figure 2 Variations of elemental concentrations with the increasing elevation.

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and Pb) suggest that anthropogenic contributions of these elements, if present, are minimal.

The variations of elemental concentrations at different elevations have been investigated in many experiments. By studying snow trace metal chemistry in Chamonix Valley and Maurienne Valley in the Alps region, Veys-seyre et al.[16] indicated that the trace metal concentra-tions tend to decrease with increasing elevation. Varia-tions of crustal ion concentrations (e.g. Ca2+ and Mg2+) in summer snow from 5800 to 7000 m on Mt. Xixa-bangma also followed the decreasing trend with eleva-tion ascent, reflecting the vertical distribution of dust aerosols in the atmosphere[17]. As shown in Figure 2, there are no clear trends for element concentration with elevation for Mt. Qomolangma snow samples. High concentrations of major elements (e.g. Ca, Mg, Fe) were observed at 7500 m, possibly due to the influence of very local inputs of crustal dust[9] since this site is close to bare rock. In addition, most elements have high con-centrations at the summit of Mt.Qomolangma, which may be due to pollutants caused by climbers who gather at the site when they reach the summit. This indicates the pristine condition of the summit, with potential con-tamination from human activities. Observed meteoro-logical data at the col of East Rongbuk Glacier (6518 m a.s.l) showed that the average daily wind speed is 7.52 m/s with the maximum value of 18.8 m/s during the pe-riod of May 1 to 22[19] with wind speeds at higher eleva-tion areas of Mt. Qomolangma greatly exceeding those at 6518 m[9]. These strong winds could redistribute the surface snow and/or shift crustal aerosols short distances from nearby rock areas onto the snow[18]. Thus, surface snow redistribution and local crustal aerosol inputs may change the vertical profile of chemical species in the free atmosphere, causing a random altitudinal trend for crustal elements (or other trace elements) in snow on Mt. Qomo-langma. 2.2 Comparison of elemental concentrations

To date, the only available referenced data in the ul-tra-high elevation area of Mt. Qomolangma were pro-vided by the Third Comprehensive Scientific Expedition Team to Mt. Qomolangma in 1975. Although the sam-pling equipment and detection techniques had great dif-ference between the two studies, it is still valuable to compare elemental concentrations between these two datasets. As shown in Table 1, elemental concentrations in the 2005 samples were lower than in the 1975 ones,

except for few elements at certain elevations. Some elements (e.g. Al and Zn), have concentrations to be two orders of magnitude lower in 2005 samples than in 1975 ones. Comparison of the mean elemental concentrations revealed that all elements in 2005 samples have lower concentrations than in 1975 ones except for Sb. Notably, concentrations of Pb in 1975 samples are higher than 10 ng/g above the elevation of 7000 m, however, Pb was not detected in most of 2005 samples, and those meas-ured Pb concentrations are far lower than 1975 samples. As discussed above, Cr, Co, Cd, and Cs were under de-tection limits in most 2005 samples. Therefore, we sug-gest that elemental concentrations measured in 2005 samples are more reliable due to advanced sampling methods and analyzing techniques. The dataset we pre-sent here provides the atmospheric environment back-ground in the ultra-high elevation area of Mt. Qomo-langma.

To further understand the environmental significance of the elemental concentrations in Mt. Qomolangma samples, data of elemental concentration in precipitation from other regions in the world were cited and organized for comparison (Table 2). The data include precipitation in remote polar regions, such as fresh snow from the Asuka site in Antarctica[20], snow samples from the Atqasuk site in Artic[21], snowpit samples (1991―1995) collected from Central Greenland[22] and from the col of Rongbuk Glacier (6500 m a.s.l.), fresh snow from dif-ferent elevations from Chamonix Valley[16] in the Alps region and precipitation from Athens[23] which repre-sents large cities influenced by intensive human activi-ties.

Concentrations of major elements (i.e. Na, Ca, K, and Ca) display larger differences between samples from Mt. Qomolangma and polar regions. Concentrations of Ca in Mt. Qomolangma samples are much higher than those in snow samples from Atqasuk site in Arctic, resulting from crustal aerosol deposition in snow from local bare rock sources in spring as discussed above. Relatively high concentrations of Na and Mg in Atqasuk samples are interpreted as input of sea salt spray[23]. Concentra-tions of trace metals (i.e. Zn, Mn, Cu, As, V, Cr) in Qo-molangma surface snow are comparable to sites in polar regions, while being far lower than those in Athens (es-pecially for Cu and Zn). This reflects the nominal an-thropogenic influence on the ultra-high elevation area of Mt. Qomolangma, which can be regarded as a represen-

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Table 1 Comparison of elemental concentrations (ng/g) in 2005 samples and 1975 samples from the ultra-high elevation area 7000 m 7500 m 8100 m 8844 m Mean

1975 2005 1975 2005 1975 2005 1975 2005

1975 2005

Na 665 38.38 705 230.4 745 186.2 92 476.9 551.75 233 Ca 17300 307.2 7000 7601 21750 1194 3705 1756 12438 2715 K 264 25.24 580 241 770 93.52 84 130.1 424.5 122.5 Mg 391.5 7.852 3250 204.4 4940 36.52 238 270 2204 129.7 Al 56.3 2.706 700 6.745 950 8.893 86 10.89 448 7.31 Cu 1.6 1.188 16.5 0.224 23.7 0.173 5.8 1.196 11.9 0.695 Fe 4 10.77 710 15.47 800 15.25 1425 19.86 734.75 15.34 Mn 0.9 1.297 36 0.75 34.9 5.708 8.4 3.999 20.05 2.94 Zn 4.1 2.717 4658 <D.L. 13900 0.701 35 9.567 4649 3.25 As 0.7 0.069 0.7 0.21 4.8 0.059 0.1 0.226 1.575 0.141 Sb 0.5 2.302 0.1 10.23 0.4 <D.L. <D.L. 1.184 0.25 3.429 Pb 0.3 0.006 60 0.02 24.7 <D.L. 17.2 0.026 25.55 0.013 <D. L.: under detection limit.

Table 2 Mean elemental concentrations (ng/g) in Mt. Qomolangma samples and comparison with data in precipitation from other regions

Mt. Qomolangma Arctic Antarctica Greenland Rongbuk Glacier Alps Athens

Surface snow mean SD

snowfall Fresh snow Snowpit Snowpit

Fresh snow

Precipitation Na 324.8 538.0 1720 0.2―80 K 129.7 225.3 140 <180 Ca 1852 2582 270 Mg 68.42 86.49 360 <200 Al 4.46 4.09 158 0.05―6 7.3 29.11 5.87 Fe 11.48 4.34 93 33.1 4.88 V 0.139 0.073 0.35 0.154 Mn 1.958 2.133 3.32 <0.5 0.41 3.61 Cu 0.343 0.367 <0.7 4.65 0.044 0.08 154 Zn 2.032 2.390 1.4 <0.5 51 1.3 0.34 33.5 As 0.183 0.295 0.11 0.84 Sb 2.95 2.82 0.9

tative of background atmospheric environment in the remote regions of the world. Surprisingly, elemental concentrations in fresh snow from Chamonix Valley are generally lower than Mt.Qomolangma samples, due to too short time delay between the end of the snowfall and field sampling, thus the samples received less subse-quent dry deposition from local sources[16]. This sug-gests that dry deposition after snowfall plays a signifi-cant role in snow chemistry.

3 Conclusion

We present elemental concentrations in surface snow samples from the ultra-high elevation area of Mt. Qo-molangma. There are no clear trends for variations in element concentrations with elevation, possibly due to local crustal aerosol inputs or redistribution of surface snow by strong winds in spring. The relatively high concentrations of trace metals are possibly due to pol-

lutants introduced by climbers, contaminating the pris-tine condition of the summit. Comparison with samples from the same elevation in 1975 showed that elemental concentrations are lower in 2005 samples than in 1975 samples, except for several elements. This suggests the better reliability of 2005 observation compared with 1975, due to advanced sampling methods and analysis techniques. Elements (especially heavy metals) on Mt. Qomolangma are comparable with polar sites and other remote sites and are far lower than large cities such as Athens. This indicates that anthropogenic activities and heavy metal pollution have little effect on the Mt. Qo-molangma atmospheric environment, which is a repre-sentative of the background atmospheric environment in the remote regions of the world.

The authors thank mountain climbing and mapping team for sampling and Dr. Gao D Y for lab work assistance.

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