Atmospheric Environment 38 (2004) 2819–2829

ARTICLE IN PRESS

AE International – Asia

*Correspond

6284 9886.

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doi:10.1016/j.at

Seasonal differences in snow chemistry from thevicinity of Mt. Everest, central Himalayas

Shichang Kanga,b,d,*, Paul A. Mayewskib,c, Dahe Qind, Sharon A. Sneedb,Jiawen Rend, Dongqi Zhange

a Institute of Tibetan Plateau Research, CAS, 18 Shuangqing Road, Beijing 100085, ChinabClimate Change Institute, University of Maine, 303 Bryand Hall, Orono, ME 04469, USA

cDepartment of Earth Sciences, University of Maine, Orono, ME 04469, USAdKey Laboratory of Ice Core and Cold Regions Environment, Cold and Arid Regions Environment and Engineering Research Institute,

CAS, Lanzhou 730000, ChinaeChinese Academy of Meteorological Sciences, Beijing 100081, China

Received 8 September 2003; received in revised form 6 January 2004; accepted 25 February 2004

Abstract

During August and September 1998, fresh snow samples were collected in the East Rongbuk (ER) Glacier on the

northern slope of Mt. Everest over an elevation range 5800–6500m. Three snowpits were sampled in the ER glacier at

an elevation of 6400, 6500, and 6500m in August 1998, May 2000 and October 2002, respectively. Snow chemical data

from fresh snow and snowpit samples from the ER Glacier are shown to be consistent with earlier results reported by

other researchers from the vicinity of Mt. Everest. Among major ions, Ca2+ has the most striking seasonal differences:

non-monsoon snow Ca2+ concentration is one order of magnitude higher than monsoon value. A large seasonal

difference characterizes fresh snow SO42� but does not seem to persist in snowpit samples probably as a consequence of

post-depositional ion elution. Non-monsoon snow Na+, K+ and Cl� are close to two times higher than monsoon snow

for both fresh snow and snowpit samples. Magnesium has distinct seasonal variations in snowpit samples and a four-

fold higher concentration in non-monsoon snow than that in monsoon snow. Seasonal differences in major chemical

composition in snow over the Mt. Everest region provide a definitive indicator for precisely dating ice cores and as a

consequence are essential in reconstructing the history of climate change and atmospheric chemistry in this region.

r 2004 Elsevier Ltd. All rights reserved.

Keywords: Fresh snow; Snowpit; Major ions; Seasonal variations; Mt. Everest region

1. Introduction

Studies of climate change as recorded in ice cores

from/near the Mt. Everest region in the central

Himalayas have increased in recent years (Hou et al.,

2002; Qin et al., 2000, 2002; Thompson et al., 2000;

Kang et al., 2001a, b, 2002a, b; Yao et al., 2002). Dating

accuracy is essential to the reconstruction of ice core

ing author. Tel.: +86-10-6284 9071; fax: +86-10-

ess: shichang.kang@itpcas.ac.cn (S. Kang).

e front matter r 2004 Elsevier Ltd. All rights reserve

mosenv.2004.02.043

climatic records and a primary dating method is the

measurement of seasonal variations in chemical species.

To validate seasonal timing of chemical species it is

necessary to establish input timing.

Due to the severe winter weather and the difficult

logistics encountered in the high regions of the

Himalayas, continuous year round precipitation sam-

pling is rarely accomplished. However, during the last

decade, studies on snow chemistry in the central

Himalayas have been undertaken, in order to evaluate

the impact of anthropogenic pollution on high elevation

remote regions. Up to now, chemical data from fresh

d.

ARTICLE IN PRESSS. Kang et al. / Atmospheric Environment 38 (2004) 2819–28292820

snow events are mainly available for two seasons:

monsoon and pre-monsoon seasons from both the

northern and southern slopes of Mt. Everest (Jenkins

et al., 1987; Valsecchi et al., 1999; Marinoni et al., 2001;

Shrestha et al., 2002) and its vicinity, such as Mt.

Xixabangma (B100 km from Everest) (Mayewski, 1986;Kang et al., 2002c), Mt. Cho Oyu (B40 km from

Everest) (Balerna et al., 2003), and Hidden Valley

(Shrestha et al., 1997). Short-term fresh snow and

aerosol chemistry sampling during monsoon and post-

monsoon seasons has shown low pollutant concentra-

tions in the Himalayan atmosphere suggesting these sites

are representative of the remote troposphere (Wake

et al., 1994; Shrestha et al., 1997; Kang et al., 2002c;

Marinoni et al., 2001). Comparisons of fresh snow

chemistry from central Himalayas and investigation of

sources of major ions indicate that variations of snow

chemistry are strongly influenced by the seasonality

other than geographical locations (Marinoni et al., 2001;

Kang et al., 2002c; Balerna et al., 2003).

A recent study of a shallow ice core from Mt.

Xixabangme indicates that spring (pre-monsoon season)

and late summer (monsoon season) are key periods in

seasonal variations in snow chemistry in the region

(Kang et al., 2000). The highest values of ion concentra-

tions in snow occur in spring (Wake et al., 1993; Kang

et al., 2000), resulting from dust deposition during the

peak in the dust-storm activity—mainly April and May

over Asia (Parrington et al., 1983; Gao et al., 1992; Qian

et al., 1997). The lowest values of ion concentrations

occur in late summer (Wake et al., 1994; Kang et al.,

2000), reflecting not only decreased dust deposition

(Wake et al., 1994; Shrestha et al., 1997), but also the

effect of increased precipitation washing out aerosols

(Kang et al., 2002c). This seasonal alternation has been

confirmed by fresh snow chemistry studies from the

vicinity of Everest (Marinoni et al., 2001; Shrestha et al.,

2002; Balerna et al., 2003).

In order to evaluate the dependability of using ice core

records to reconstruct past atmospheric change, some

studies focused on how closely snow chemistry repre-

sents atmospheric chemistry by comparing of chemical

compositions between snow and aerosols (Shrestha et al.,

1997) and between wet, dry and snow deposition

(Valsecchi et al., 1999), suggesting that some chemical

species (e.g. NO3�, Cl�, NH4

+) deposited in snow are

influenced by post-depositional processes such as

absorption and scavenging of gaseous species (HCl,

HNO3, NH3) from the atmosphere. A comparison of

two adjacent ice core records from glacier accumulation

zone and percolation zone, respectively, on the northern

slope of Mt. Everest (Hou et al., 2002) shows that the

overall features of the d18O profiles of the two cores aresimilar, while a significant discrepancy exists for the

ionic profiles of the two cores due to post-depositional

modification processes (e.g. the elution process, chemical

reactions). The dramatically decreased NH4+ and SO4

2�

concentrations in the core from percolation zone could

be caused by the ion elution process that moved most

chemicals away with runoff (Hou et al., 2002).

The meteorological and pluviometric regime of the

Asian continent is mainly controlled by polar air masses

from the Arctic, continental air masses from central

Asia, and maritime air masses from the Pacific and

Indian Oceans (Bryson, 1986). The location of the East

Rongbuk (ER) Glacier on Mt. Everest (27�590N,

86�550E) (Fig. 1) at the boundary of the South Asian

monsoon (Indian monsoon) and the continental climate

of central Asia, combined with the high elevation of the

site (6500m, well above the influence of the boundary

layer), offers a unique opportunity to describe and

understand change in climate and chemistry of the

atmosphere over Asia.

Here we present chemical data from fresh snow

sampled in August and September 1998 and three

snowpits sampled in August 1998, May 2000 and

October 2002 from the ER Glacier (Fig. 1) on the

northern slope of Mt. Everest, and compare our data

with existing results from the region. The main purpose

of the present work is to expand the snow chemistry

database for the high mountain regions of the Hima-

layas, and to expand our knowledge of the spatial and

temporal characteristics of snow chemistry in the Mt.

Everest region. In particular, we focus on the differences

between snow chemistry from monsoon and non-

monsoon seasons and verify the significance of this

seasonal difference as applied to high precision ice core

dating.

2. Methods

During August and September 1998, a total of 39

fresh snow samples were collected on the ER Glacier on

the northern slope of Mt. Everest (27�590N, 86�550E).

Our sampling sites were at nine sites between 5800 and

6500m (Fig. 1). Eight storm events were sampled. For

logistical reasons, not all elevations could be sampled for

each event. Three snowpits in the ER Glacier were

sampled continuously at 5 cm depth interval in August

1998, May 2000 and October 2002, respectively.

Sampling methods for fresh snow and snowpit are the

same as those used by Mayewski (1986), Wake et al.

(1993, 1994) and Kang et al. (2000, 2002c). Extreme care

was taken at all times during sample collection and

handling to assure samples were not contaminated. For

example, non-particulating suits, polyethylene gloves

and masks were worn at all times during sampling. Pre-

washed high-density polyethylene HDPE containers

were used as sample scoops. Field blanks were collected,

filled with ultrapure water in the laboratory, opened

during sample collection and handled as samples.

ARTICLE IN PRESS

Fig. 1. Map of sampling sites for fresh snow and snowpits in the East Rongbuk Glacier on the northern slope of Mt. Everest, central

Himalayas.

S. Kang et al. / Atmospheric Environment 38 (2004) 2819–2829 2821

Samples were kept frozen in the field, during transporta-

tion, and in the laboratory until analysis. All of these

sampling techniques have been demonstrated to mini-

mize or eliminate contamination (Wake et al., 1994).

Analysis of duplicate samples as well as field and

laboratory blanks indicates that sample contamination

during sample collection, transport, and subse-

quent analytical procedures is negligible. Major ion

ARTICLE IN PRESSS. Kang et al. / Atmospheric Environment 38 (2004) 2819–28292822

(NO3�, Cl�, SO4

2�, NH4+, Ca2+, Na+, K+ and Mg2+)

concentrations were measured at the Climate Change

Institute, University of Maine, USA, using a Dionex Ion

Chromatograph model DX-500. Detailed methods are

described by Buck et al. (1992) and Wake and Mayewski

(1993).

3. Results and discussions

3.1. Chemical composition of fresh snow samples

The mean composition and standard deviation of all

1998 fresh snow samples and each snowfall event are

given in Tables 1 and 2. We calculated the ion balance

DC (sum of cations—sum of anions) for each sample;

the mean value of DC; �0.03meq l�1 (Table 2), indicatesa balance between major cations and anions for our

fresh snow samples. With respect to the sea-salt ratio

(0.86), the ratios of Na+/Cl� from Mt. Everest fresh

snow are very low, with a mean value of 0.30 (Table 2)

and only one event having a ratio higher than 0.86

(Table 1), indicating that there is a large excess of Cl� in

our samples. This is consistent with results from fresh

snow over the Cho Oyu range (Balerna et al., 2003) and

ice core chemical records from the ER Glacier (Kang

et al., 2002b), but in disagreement with the results from

the southern slope of the Nepal Himalayas (Marinoni

Table 1

Mean chemical composition and standard deviation (7) of fresh snoevent (unit: meq l�1)

Date Na+ NH4+ K+ Mg2+ Ca2+ Cl�

30 Aug 0.25 0.01 0.22 0.33 2.63 0.76

70.37 70.02 70.27 70.18 71.74 70.15

31 Aug 0.15 0.09 0.03 0.12 0.16 0.89

70.14 70.10 70.06 70.06 70.19 70.09

Sep 1 +DL 0.19 +DL 0.15 0.15 0.85

Sep 2 0.10 0.28 +DL 0.12 0.92 0.83

Sep 4 0.08 0.88 +DL 0.31 0.56 1.01

Sep 5 0.51 0.06 0.28 0.44 5.63 1.75

70.28 70.10 70.04 70.14 71.14 70.30

Sep 6 0.51 3.72 0.21 0.44 6.11 1.23

70.35 73.76 70.10 70.27 71.13 70.50

Sep 29 1.70 0.53 0.49 0.29 2.40 1.05

72.01 70.81 70.50 70.11 71.20 70.86

DC=([NH4+]+[Ca2+]+[Na+]+[K+]+[Mg2+])�([NO3

�]+[Cl�]+[SO

et al., 2001; Valsecchi et al., 1999), in which the Na+/

Cl� ratios during the monsoon period are very similar to

the classical sea-salt ratio showing the strong marine

contribution related to the monsoon circulation. The

excess Cl� can be explained assuming an enrichment of

Cl� in the snow due to the scavenging of HCl in the

atmosphere. This is supported by comparison between

ion concentrations in snow and aerosols over the

Hidden Valley (Shrestha et al., 1997) and the southern

slope of Mt. Everest (Shrestha et al., 2002). On the other

hand, Na+ and Cl� may have different sources during

the monsoon season. Kang et al. (2002b) has performed

Empirical Orthogonal Function (EOF) analysis for

major ion concentration of the ER ice core to classify

the chemical species in the ice core. EOF analysis allows

a more robust assessment of the behavior of several

variates and also provides new time-series that represent

their relationships. EOF decomposition provides objec-

tive representations of multivariate data through the

analysis of the covariance structure of its variates (e.g.

Meeker et al., 1995). The results form this analysis

indicate that the EOF2 mainly loaded with K+ and Cl�

representing crustal species from, for example, KCl-rich

deposits transported by summer atmospheric circulation

from local or regional sources. Although the source of

the KCl-rich deposits cannot be specified from our

study, a possible source may be local or regional

(around the north and south of Himalayas) mineral

w from the northern slope of Mt. Everest by individual storm

NO3� SO4

2� DC Na+/Cl� No. of

samples

Elevation

(m a.s.l.)

1.31 1.16 0.23 0.30 8 6300–6500

71.26 70.36 72.03 70.38

0.25 0.44 �1.00 0.16 18 6300–6500

70.14 70.15 70.39 70.14

0.97 0.61 �1.92 1 6500

0.17 0.85 �0.42 0.12 1 6300

0.80 0.55 �0.52 0.08 1 6450

4.56 1.14 �0.53 0.28 3 6300–6450

73.82 70.51 73.29 70.14

5.74 1.57 2.46 0.39 2 6450

70.57 71.07 71.22 70.13

0.46 0.50 2.92 0.93 5 5800–6200

70.47 70.35 73.46 70.70

42�]); DL: detection limit.

ARTICLE IN PRESS

Table 2

Mean major ion concentrations and standard deviation (7) of fresh snow and snowpit samples from the East Rongbuk Glacier on thenorthern slope of Mt. Everest (unit: meq l�1)

Number Sampling Elevation Na+ NH4+ K+ Mg2+ Ca2+ Cl� NO3

� SO42� DC Na+/Cl� Depth

(cm)

No. of

sample

Date (m a.s.l.)

Fresh

snow

August–September

1998

5800–6500 0.41 0.34 0.15 0.23 1.71 1.02 1.14 0.72 �0.03 0.30 39

70.86 71.06 70.26 70.16 72.13 70.45 71.90 70.48 71.64 70.40

Snowpit 1 August 1998 6400 0.71 0.08 0.46 0.49 4.85 1.29 0.18 0.69 4.43 0.35 55 11

71.16 70.10 70.54 70.57 79.02 70.06 70.03 70.35 710.38 70.52

Snowpit 2 May 2000 6500 0.75 1.41 0.29 0.35 8.26 0.90 1.37 0.69 8.11 0.65 125 24

70.98 70.92 70.25 70.48 720.31 70.64 71.39 70.46 720.45 70.37

Snowpit 3 October 2002 6500 0.54 Nd 0.24 0.21 2.79 0.55 1.32 0.80 1.13a 0.81 360 74

70.90 70.35 70.20 75.15 70.69 71.13 70.42 74.69 70.30

DC=([NH4+]+[Ca2+]+[Na+]+[K+]+[Mg2+])�([NO3

�]+[Cl�]+[SO42�]); nd: not determined.

anot included [NH4+].

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9

Monsoon Pre-monsoon

Ca2+ SO42-Na+ NO3

- Cl-

38.0

1 East Rongbuk Gl., northern slope of Mt. Everest (5800-6500 m a.s.l., Aug.-Sept. 1998, sample number n=39); Present work2 Gyabrag Gl., northern slope of Mt. Cho Oyu (5671-5730 m a.s.l., Sept. 2000, n=7); Balerna et al., 20033 Dasuopu Gl., northern slope of Mt. Xixabangma (5400-7000 m a.s.l., Aug.-Sept. 1997, n=102); Kang et al., 20024 Khumbu Valley, southern slope of Mt. Everest (5050-6050 m a.s.l., Sept.-Oct. 1998, n=17); Marinoni et al., 20015 Khumbu Valley, southern slope of Mt. Everest (5050 m a.s.l., July-Aug., 1992, n=19); Valsecchi et al., 19996 Hidden Valley, Dhaulagiri peak (5050-5700 m a.s.l., Aug. 1994, n=28); Shrestha et al., 19977 Middle Rongbuk Gl., northern slope of Mt. Everest (5600-7100 m a.s.l., Apr.-May 1986, n=96); Jenkins et al., 19878 Northern slope of Mt. Xixabangma (6300 m a.s.l., May 1984, n=6); Mayewski et al., 19869 Island peak, southern slope of Mt. Everest (5300-6100 m a.s.l., May 1994, n=3); Marinoni et al., 2001

* Data are not available.

* *

Ion

conc

entr

atio

ns (

ueq

L-1)

Fig. 2. Comparison of ion concentrations (meq l�1) between monsoon and pre-monsoon fresh snow samples collected in the vicinity ofMt. Everest, central Himalayas.

S. Kang et al. / Atmospheric Environment 38 (2004) 2819–2829 2823

aerosols (Shrestha et al., 1997; Thompson et al., 2000)

that are deposited mainly during the summer season

which we assume because of their connections to

summer atmospheric circulation (Kang et al., 2002b).

In order to investigate the seasonal differences of

major ion concentrations in fresh snow over the vicinity

of Mt. Everest, all data from recent research in the

region is plotted in Fig. 2, to reveal a comparison

between fresh snow chemistry during monsoon and pre-

monsoon seasons. The fresh snow compositions from

the ER Glacier are in accordance with concentrations of

monsoon fresh snow samples collected on both northern

ARTICLE IN PRESSS. Kang et al. / Atmospheric Environment 38 (2004) 2819–28292824

and southern slopes of the region, but far lower than

those from fresh snow in pre-monsoon season (Fig. 2).

In addition, for the entire dataset available in this

region, ion concentrations of pre-monsoon samples are

much higher than those of monsoon ones, especially

Ca2+ and SO42� concentrations (Fig. 2).

Calcium concentrations range between 1.71 and

6.44meq l�1 in monsoon fresh snow, and jump to 12.6–38.0meq l�1 in pre-monsoon fresh snow (Fig. 2). Pre-monsoon Ca2+ concentrations are one order of magni-

tude higher than the monsoon concentrations. Pre-

monsoon fresh snow SO42� concentrations vary from 5.8

to 15.9meq l�1, one to two orders of magnitude higherthan monsoon values (0.25–1.38 meq l�1) (Fig. 2).Differences in NO3

� between pre-monsoon and monsoon

season are apparent but not as much as those for Ca2+

and SO42�. Pre-monsoon Na+ and Cl� concentrations in

fresh snow are roughly double higher than those during

monsoon season (Fig. 2). Pre-monsoon NH4+, K+ and

Mg2+ concentrations, available only from one report

(Island Peak, southern slope of Mt. Everest (Marinoni

et al., 2001)), are also higher than those in monsoon

samples, and differences in the three species between two

seasons are similar to those of Na+ and Cl�.

There is one dataset of major ion concentrations for

post-monsoon fresh snow sample from Mt. Cho Oyu

reported by Balerna et al. (2003). Comparison shows

post-monsoon fresh snow also has higher ion concen-

trations than monsoon fresh snow, especially for Ca2+,

SO42� and NO3

�. This further confirms that low

concentrations of major ions in fresh snow occur during

monsoon season in the high elevation regions of the

central Himalayas, as noted by earlier researchers (Wake

et al., 1994; Marinoni et al., 2001; Kang et al., 2000;

Balerna et al., 2003). The low ion concentrations of

monsoon snow may reflect both decreased dust deposi-

tion (Wake et al., 1994; Shrestha et al., 1997) and

increased precipitation that washes out aerosols (Kang

et al., 2002c). The high ion concentrations in pre-

monsoon snow may result from dust deposition during

the peak in the dust-storm activity mainly in April and

May over Asia (Parrington et al., 1983; Gao et al., 1992;

Qian et al., 1997).

We also investigate the spatial distribution of fresh

snow chemical compositions in the vicinity of Mt.

Everest, in order to understand whether the crest of the

Himalayas is an effective barrier for transportation of

monsoon moisture from the south or dust storms from

the north, which is crucial to the interpretation of ice

core records recovered from the region. During mon-

soon season, Ca2+ concentrations in fresh snow are

higher in Mt. Cho Oyu (2) and the Hidden Valley (6),

both located in the northern slope of the Himalayas,

than those in other sites (Fig. 2), meanwhile, Ca2+

concentrations from two other northern sites: the ER

Glaciers (1) and the Dasuopu Glacier (3), are quite close

to the values in southern locations—the Khumbu Valley

(4, 5). For other species, the concentrations are more

homogeneous during monsoon season, and not as

dependent on geographical location as those on the

southern or northern slope of the Himalayas. Studies

also show that, during the pre-monsoon season, most of

major ions (e.g. Ca2+, SO42�, NO3

�) come from dust

deposition over the central Himalayas (Wake et al.,

1993; Kang et al., 2000). It seems that pre-monsoon

Ca2+, Na+ and Cl� concentrations are higher on the

northern slope of Mt. Everest and Xixabangma than

those on the southern slope of Mt. Everest (Fig. 3).

However, pre-monsoon SO42� concentrations are lower

on the northern slope of Mt. Everest than those on the

southern slope, while NO3� concentrations do not show

gradients between the northern and southern slopes.

Therefore, differences in fresh snow compositions

between the northern and southern slopes of the Mt.

Everest are not large compared with those between

monsoon and non-monsoon seasons. This may suggest

that the crest of the Himalayas is not a very effective

barrier to the spatial distribution of ion concentrations

in fresh snow for both pre-monsoon and monsoon

seasons, at least in the high mountain region of Mt.

Everest. More data will be needed to further understand

the role of the Himalayas in the distribution of snow

chemistry.

3.2. Chemical composition of snowpit samples

Table 2 summaries the mean ion concentrations for

snowpit samples collected from the ER Glacier on the

northern slope of Mt. Everest. Despite the different

sampling dates and snowpit depths, major ion concen-

trations from the three snowpits are consistent. An

obvious feature of snowpit chemistry is that Ca2+

concentrations are far higher than those of other species.

Comparison of ion concentrations between our 1998

fresh snow and three snowpits shows that, except for

Ca2+ concentrations, most of the species have similar

concentrations (Table 2). Our fresh snow samples have

very similar cation and anion concentrations, however,

a large excess of cations exists for snowpit samples due

to high Ca2+ concentrations (Table 2). This can be

comprehended considering that snowpits comprise

multi-season samples. Snowpit Na+/Cl� ratios suggest

that there is also an excess of Cl� compared to the sea-

salt Na+/Cl� ratio, in accord with results for fresh snow

samples.

Major ion concentrations versus depth for three

snowpits are presented in Figs. 3–5. Snowpit 1, elevation

of 6400m (Table 2), is located above the average

equilibrium line of the ER Glacier and the bottom of

the pit (close to an icy crust) is slightly dirty and

represents spring dust deposition. The variations of

Ca2+ concentration with depth show that Ca2+ spikes

ARTICLE IN PRESS

Fig. 3. Ion concentrations (meq l�1) versus depth in snowpit 1 collected in August 1998 at an elevation of 6400m in the East RongbukGlacier on the northern slope of Mt. Everest. Vertical dashed line represents the seasonal boundary.

S. Kang et al. / Atmospheric Environment 38 (2004) 2819–2829 2825

occurs in that layer (45–55 cm) (Fig. 3). From the top to

a depth of 45 cm in snowpit 1, ion concentrations are

relatively low, representing monsoon snow deposition.

Thus, we divide snowpit 1 into two seasons marked by a

dashed vertical line (Fig. 3). Most of the ions have

increasing concentrations in non-monsoon (or spring)

snow, except for NO3�.

Similar methods are applied to identify the monsoon

and non-monsoon snow layers for snowpits 2 and 3. For

snowpit 2, collected in May 2000, high ion concentra-

tions occur in the upper 30 cm snow representing non-

monsoon season deposition, following low ion concen-

trations at a depth of 30–85 cm related to monsoon

season snow, and high ion concentrations in the bottom

related to another non-monsoon season snow (Fig. 4).

The striking spikes of Ca2+ concentrations appear in

both non-monsoon snow layers with values as high as

88.5 and 55.4meq l�1. Detailed examination reveals thatNa+ and Cl� have more similar spikes (Fig. 4), so do

Ca2+ and Mg2+, reflecting close source region or

transport way for both species.

Snowpit 3 sampled in October 2002 has four

distinguishable monsoon and non-monsoon snow layers

(Fig. 5). High Ca2+ and Mg2+ concentrations are in

non-monsoon snow layers. Besides the spikes of Na+,

Cl� and K+ concentrations in non-monsoon seasons,

ARTICLE IN PRESS

Fig. 4. Ion concentrations (meq l�1) versus depth in snowpit 2 collected in May 2000 at an elevation of 6500m in the East RongbukGlacier on the northern slope of Mt. Everest. Vertical dashed lines represent the seasonal boundaries.

S. Kang et al. / Atmospheric Environment 38 (2004) 2819–28292826

high values of the three species also occur in monsoon

season of 2002 (at a depth of 50 and 90 cm) (Fig. 5).

Indeed, the monsoon peaks of three species can be

observed in both snowpit 1 (the depth of 35 cm) (Fig. 3)

and snowpit 2 (around 60 cm) (Fig. 4). High concentra-

tions of these species may be caused by local or regional

crustal aerosol input related to the summer circulation

as reported by Kang et al. (2002b). Sulfate and NO3�

also show spikes not only in non-monsoon snow layers

but also in monsoon layers.

Mean chemical composition of monsoon and non-

monsoon snow from three snowpits is calculated and

presented in Fig. 6. For snowpit samples collected in the

ER Glacier on the northern slope of Mt. Everest, there

is a striking seasonal difference for Ca2+ that is more

distinct than those for other species. Non-monsoon

snow Ca2+ is one order of magnitude higher than that

of monsoon Ca2+, consistent with the fresh snow

samples. Compared with the dramatic difference in

fresh snow SO42� between monsoon and pre-monsoon

seasons (one to two orders of magnitude) (Fig. 2), the

seasonal difference from snowpit samples is minor. The

ion elution process may cause the significant decrease of

SO42� concentrations in snow pack (Hou et al., 2002),

altering the original higher SO42� concentrations in non-

monsoon snow layers. Non-monsoon snow Na+, K+

and Cl� concentrations from snowpits are nearly two

times higher than monsoon values (Fig. 6), which agrees

with the fresh snow samples. The seasonal difference in

NO3� in snowpits is similar to that in fresh snow. Like

Ca2+, it seems that Mg2+ has more distinct seasonal

variations than other ions (Fig. 6): non-monsoon Mg2+

concentrations are about four fold higher that monsoon

values in snowpit samples.

ARTICLE IN PRESS

Fig. 5. Ion concentrations (meq l�1) versus depth in snowpit 3 collected in October 2002 at an elevation of 6500m in the East RongbukGlacier on the northern slope of Mt. Everest. Vertical dashed lines represent the seasonal boundaries.

Fig. 6. Comparison of mean ion concentrations (meq l�1) between monsoon and non-monsoon snow from three snowpit samplescollected in the East Rongbuk Glacier on the northern slope of Mt. Everest, central Himalayas.

S. Kang et al. / Atmospheric Environment 38 (2004) 2819–2829 2827

ARTICLE IN PRESSS. Kang et al. / Atmospheric Environment 38 (2004) 2819–28292828

Seasonal differences in snow chemical composition in

the vicinity of Mt. Everest offer a definitive indicator for

precisely dating ice cores and hence reconstructing past

change in climate and atmospheric chemistry. Snow

chemistry data from both fresh snow and snowpit

samples reveal that notable differences in Ca2+ con-

centrations exist between monsoon and non-monsoon

seasons, indicating that Ca2+ is perhaps the most

definitive ion for precise dating. Other species serve as

secondary references for dating ice cores.

4. Summary and conclusions

Snow chemical data from fresh snow and snowpit

samples collected in the ER Glacier on the northern

slope of Mt. Everest presented in this paper expand the

database of snow chemistry in the remote and high

mountain regions in the vicinity of Mt. Everest. Ion

balance calculations indicate that monsoon fresh snow

samples are in balance, however, snowpit samples have

an excess of cations due to high Ca2+ concentrations in

non-monsoon season. Fresh snow Na+/Cl� ratio shows

an excess of Cl� , relative to the sea-salt Na+/Cl� ratio,

in accord with the results from snowpit samples,

probably due to the scavenging of HCl in the air and/

or different sources between Na+ and Cl�.

Major ion concentrations from our 1998 fresh snow

samples collected during the monsoon season are similar

to other available data for monsoon fresh snow, but are

far lower than those for pre-monsoon season in the

vicinity of Mt. Everest. Comparison of chemical data

between monsoon and pre-monsoon fresh snow shows

striking seasonal differences in Ca2+ and SO42� con-

centrations: pre-monsoon Ca2+ is one order of magni-

tude higher than monsoon value; pre-monsoon SO42�

is one to two orders of magnitude higher than monsoon

value. Differences in NO3� concentrations between

pre-monsoon and monsoon seasons are also marked

but not as dramatic as those of Ca2+ and SO42�. Pre-

monsoon Na+ and Cl� concentrations are roughly

double higher than monsoon concentrations. Investiga-

tion of the spatial distribution of snow chemistry

indicates differences between fresh snow compositions

on the northern and southern slopes of Mt. Everest

region are neglectable compared with those from

monsoon to pre-monsoon seasons. This suggests that

the crest of the Himalayas is not a completely effective

barrier to the spatial distribution of fresh snow

chemistry during either non-monsoon or monsoon

seasons at least in the high mountain regions in the

vicinity of Mt. Everest.

The glaciochemistry from three snowpits collected in

the ER Glacier agrees with results from fresh snow in

the region. Calcium has the most striking seasonal

differences: non-monsoon snow Ca2+ is one order of

magnitude higher than that of monsoon snow consistent

with fresh snow samples. The dramatic seasonal

difference in fresh snow SO42� does not exist in snowpits

probably due to the ion elution process. Non-monsoon

snow Na+, K+ and Cl� concentrations from snowpits

are close to two times higher than monsoon values, in

agreement with fresh snow samples. Magnesium also has

a distinct seasonal variation, with a four-fold concentra-

tion difference in non-monsoon compared to monsoon

snow.

Snow chemistry data from both fresh snow and

snowpit samples reveal that striking differences in Ca2+

concentrations exist between monsoon and non-mon-

soon seasons, indicating that Ca2+ is perhaps the most

definitive ion for precise dating. Other species serve as

secondary references for dating ice cores. Therefore,

seasonal differences in snow chemical composition in the

vicinity of Mt. Everest offer a tool for precisely dating

ice cores and hence reconstructing past change in climate

and atmospheric chemistry.

Acknowledgements

This research is supported by the National Natural

Science Foundation of China (40121101, 40205007);

the Chinese Academy of Science (KZCX3-SW-339,

KZCX1-10-09, 02, KZCX2-SW-118); the US National

Science Foundation (ATM-0139481); the ‘‘Talent Pro-

ject’’ of CAS. We greatly appreciate helps from Dr. Hou

and Mr. Li in the field and suggestions from referees for

the improvement of our paper.

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