A variation of stable isotope composition of snow with altitude on the Elbrus mountain, Central Caucasus

Abstract

This study aims to analyze the stable isotope composition of the snow cover of the Elbrus Mountain-the highest mountain in Europe. Snow sampled in the middle accumulation. Snow sampled at the south slope of Mt. Elbrus at different elevations, and the total altitude range is approximately 1700 m. A significant altitude effect in fresh snow precipitation was determined in February 2001 with gradient -1.3‰ δ18O/100 m (-11.1‰ δ2H /100 m) at 3100-3900 m a.s.l. and inverse altitude effect in February 2016 with gradient +1.04‰ δ18O /100 m (+8.7‰ δ2H /100 m) at 3064-3836 m a.s.l. There is no obvious altitude effect of the δ2H and δ18O values in snow at the Elbrus slope in 2017, except for the height range 2256-3716 m a.s.l., where altitudinal effect of δ18O values was roughly - 0.32‰/100m. The δ18O values in the winter snowpack in some cases decrease with increasing altitude, but sometimes are not indicating a temperature-altitude effect. Post-depositional processes cause isotopic changes, which can result from drifting, evaporation, sublimation, and ablation. The study of altitude effect in snow is important for understanding the processes of snow-ice and snow-meltwater transformation and the snow/ice potential to provide paleo-environmental data.

Full text

172
A VARIATION OF STABLE ISOTOPE COMPOSITION OF
SNOW WITH ALTITUDE ON THE ELBRUS MOUNTAIN,
CENTRAL CAUCASUS
Yurij Vasil’chuk1*, Julia Chizhova2, Natalia Frolova1, Nadine Budantseva1, Maria Kireeva1,
Alexander Oleynikov1, Igor Tokarev3, Ekaterina Rets1, Alla Vasil’chuk1
1 Lomonosov Moscow State University, Faculty of Geography, Moscow, Russia
2 Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM RAS), Moscow, Russia
3 The Centre for X-ray Diffraction Studies, Research park at St. Petersburg University, St. Petersburg, Russia
*Corresponding author: vasilch_geo@mail.ru
ABSTRACT. This study aims to analyze the stable isotope composition of the snow cover of the Elbrus Mountain – the highest
mountain in Europe. Snow sampled in the middle accumulation period in January 2017, February 2016, January 2001 and
during snowmelt in July 1998 and August 2009. Snow sampled at the south slope of Mt. Elbrus at different elevations, and
the total altitude range is approximately 1700 m. A significant altitude effect in fresh snow precipitation was determined
in February 2001 with gradient –1.3‰ δ18O/100 m (–11.1‰ δ2H /100 m) at 3100-3900 m a.s.l. and inverse altitude effect in
February 2016 with gradient +1.04‰ δ18O /100 m (+8.7‰ δ2H /100 m) at 3064-3836 m a.s.l. There is no obvious altitude
effect of the δ2H and δ18O values in snow at the Elbrus slope in 2017, except for the height range 2256-3716 m a.s.l., where
altitudinal effect of δ18O values was roughly -0.32‰/100m. The δ18O values in the winter snowpack in some cases decrease
with increasing altitude, but sometimes are not indicating a temperature-altitude effect. Post-depositional processes cause
isotopic changes, which can result from drifting, evaporation, sublimation, and ablation. The study of altitude effect in snow
is important for understanding the processes of snow-ice and snow-meltwater transformation and the snow/ice potential
to provide paleo-environmental data.
KEY WORDS: stable isotopes, spatial variability, snow cover on glaciers, high altitude, Caucasus
CITATION: Yurij Vasil’chuk, Julia Chizhova, Natalia Frolova, Nadine Budantseva, Maria Kireeva, Alexander Oleynikov, Igor
Tokarev, Ekaterina Rets, Alla Vasil’chuk (2020) A variation of stable isotope composition of snow with altitude on the Elbrus
Mountain, Central Caucasus
.
Geography, Environment, Sustainability, Vol.13, No 1, p. 172-182
DOI-10.24057/2071-9388-2018-22
INTRODUCTION
For all studies that require information about the isotopic
composition of the snowpack in a catchment, detailed infor-
mation on the spatial and temporal variability of the isotopic
content of snow is valuable. The water input in snow-dom-
inated watershed for residence time analysis, end member
mixing analysis or the detection of source water contribution
requires a detailed understanding of the eects of factors
that modify the isotopic composition of snow cover.
During orographic lift of air mass, the heavier water mol-
ecules condense at rst, i.e. the precipitation is isotopically
enriched, and the cloud moisture is subsequently depleted
due to continuous precipitation under equilibrium fraction-
ation.
Depletion of the isotopic composition of precipitation
with elevation is the “altitude isotope eect” – the altitude iso-
tope eect in precipitation well-known since the Dansgaard
(1964) research. The altitude eect is temperature-related be-
cause the condensation is caused by the temperature drop
due to the increasing altitude. Due to the decreasing pres-
sure with increasing altitude, a larger temperature decrease is
required to reach the saturated water vapor pressure than for
isobaric condensation. Moser and Stichler (1970) observed
altitudinal isotope eect in fresh snow at the Kitzsteinhorn in
Austrian Alps. An elevation gradient for δ18O values between
is −0.6 and −1.0‰ per 100 in high mountains in the snow
was determined (Niewodniczanski et al. 1981). However,
there was in a wide range of isotope values with small-scale
inverse gradient and thus only partly attributable to a linear
elevation gradient. These variations explained by conditions
during snowfall and after snow deposition, such as wind drift
and fractionation by melting processes, as well as orographic
and climatic features of the studied areas (Niewodniczanski
et al. 1981). For the fresh snow in the Canadian Rocky Moun-
tains, elevation gradients range from −0.3 to +1.8‰ per 100
m, depending on snowfall and accumulation conditions
(Moran et al. 2007).
In contrast to the altitude isotope eect in fresh snow,
the isotopic composition of an entire snowpack is more
complex (Moser and Stichler 1974). The snowpack is altered
by sublimation, evaporation, metamorphism of snow crys-
tals, percolating of meltwater and isotopically enriched pre-
cipitation, especially in temperate climatic conditions (Judy
et al. 1970; Ambach et al. 1972; Stichler et al. 2001; Sokratov
and Golubev 2009). These processes may conceal the alti-
tudinal eect in fresh snow and result in inverse gradients
(Moser and Stichler 1970). In some cases, there was no sig-
nicant relation between the isotopic signature of the entire
snowpack and elevation (Raben and Theakstone 1994; Kang
et al. 2002; Königer et al. 2008).
Dietermann and Weiler (2013) observed only a limited
altitude isotope eect in Swiss Alps. The altitudinal eect
for δ2H values at the south-facing slopes ranged from −6.2
to +2.6‰/100 m with a wide variability for the individu-
al samples. These results conrm the inuence of melting
processes altering the mean isotopic composition of snow
cover. The north-facing slope of this catchment is a steep
av-

173
Yurij Vasil’chuk, Julia Chizhova et al. A VARIATION OF STABLE ISOTOPE ...
alanche-prone slope popular for mountain skiing. These fac-
tors likely lead to snow mixing and disturbance of the altitude
isotopic eect (Dietermann and Weiler 2013).
We have found the altitudinal eect on δ18O and δ2H val-
ues of fresh snow on the southern slope of Elbrus in Janu-
ary 2001, decreasing with increasing altitude (Vasil’chuk and
Chizhova 2010). The of snow becomes more and more deplet-
ed in 18O and 2H content at higher elevations. In the range of
3100–3400 m a.s.l., the gradients are –2.4 ‰ / 100 m for Δδ18O
and –20 ‰ for Δδ2H values, and at altitudes of 3400–3900 m
they are –0.6 / 100 m for Δδ18O and –6 ‰ for Δδ2H values. We
found a decreasing d-excess values in snow at 3100 to 3400
m a.s.l. We associated high gradients at altitudes from 3100 to
3400 m with intensive washing out of the air mass and iso-
topic depletion during precipitation. However, if we assume,
based on the isotope data, the decrease of δ18O values from
–17 to –29‰ in snow with increasing altitude from 3100 to
3400 m due to progressive precipitation, the decreasing of
d-excess in this snow could not be explained.
The progressive rainout process based on the Rayleigh
fractionation/condensation model predicts increasing d-ex-
cess values in the latest stages of precipitation. Also, the equi-
librium Reyleigh condensation model including the isotopic
kinetic eect (Jouzel and Merlivat 1984) as well as isotopic
model including mixed cloud processes (Ciais and Jouzel
1994) predict relatively high values of d-excess.
In many cases, the d-excess is found to increase with alti-
tude on the mountain slopes, possibly for a variety of reasons.
This issue has not been nally resolved. Hereby, a decreasing
d-excess with decreasing δ18O values in fresh snow in Jan-
uary 2001 may indicate a very ambiguous formation of the
isotopic composition of snow cover on the southern slope of
Elbrus.
Recent studies of glaciers of Elbrus are focused on obtain-
ing information about the environmental conditions of ice
accumulation, including sources of air masses, atmospheric
conditions, and the transformation of snow to ice. The stable
isotopes and chemical composition are indicators of the pro-
cesses involved in atmospheric precipitation.
Observations of recent retreat of the Elbrus glacier system
(Vasil’chuk et al. 2006, 2010; Zolotarev and Kharkovets 2010;
Holobâcă 2016; Tielidze and Wheate 2017) show signicant
changes of the glaciers volume and their ‘tongues’ retreats
during the past 100 years, however, there appears to be no
signature in the isotopic composition of the glacier ice (Va-
sil’chuk et al. 2006).
Although most of the incoming moisture to the Elbrus
is of Atlantic origin, some air masses drift from the south-
ern deserts. The dust that originates from the foothills of the
Djebel Akhdar in eastern Libya and transported to the Cauca-
sus along the eastern Mediterranean coast, Syria and Turkey
(Shahgedanova et al. 2013) was found in snowpack of Gara-
baschi glacier.
Elbrus glacier’s ice is paleo-archive, especially at altitudes
above 4900 m, where isotope record is undisturbed by the
meltwaters due to the absence of melting at this elevation.
The isotope records of low-latitude and high-mountain gla-
ciers cores have the potential to provide detailed paleo-en-
vironmental proxy record and to prove extremely valuable in
producing continuous records of atmospheric chemistry and
climate (Thompson et al. 1998, 2006a, 2006b; Tian et al. 2003;
Yao et al. 2006). The low-latitude Tibetan cores records, espe-
cially Dunde and Dasuopu, are consistent with the local tem-
perature records (Yao et al. 2006), the more northern sites,
similar to Dunde, are thought to be more temperature-dom-
inated (e.g., Tian et al. 2003).
In recent years, deep drilling of Elbrus glaciers allowed to
obtain δ18O and δ2H records (Mikhalenko et al. 2015; Kozach-
ek et al. 2017). There was no signicant correlation between
ice core δ18O records from the western Elbrus plateau (height
5115 m a.s.l) with regional temperature, neither with the re-
analysis data nor with the data of meteostation (Mikhalen-
ko et al. 2015; Kozachek et al., 2017). At the western Elbrus
plateau, the snow accumulation rate is high and moreover,
pronounced seasonal variations of δ18O and δ2H values were
noted in the core. In spite of the presence of δ18O amplitude
in ice core, which could indicate the existence of a δ18O-tem-
perature relationship, conditions of individual snowfall play
an important role. Such conditions include snow mixing by
wind and dierent air masses with dierent source character-
istics aect the precipitation at the base and crest of a moun-
tain.
In this case, the study of the formation of an isotope al-
titude eect in snow is important for understanding this ex-
clusion of temperature eect in ice. Here, the results of iso-
tope analysis of the snow samples are presented to provide a
better understanding of the spatial and temporal features of
snow accumulation on Elbrus.
STUDY SITE
The Caucasus Mountains are located between the Black
and the Caspian Seas and generally oriented from east to
southeast, with the Greater Caucasus range often considered
as the divide between Europe and Asia. The total area of gla-
ciers in the Caucasus is about 1121±30 km2 (Mikhalenko et
al. 2015). Glaciers on the Elbrus Mountain are located in the
altitudinal range 2800-5642 m.
The coldest conditions occur above 5200 m a.s.l., where
the mean summer air temperature does not exceed 0oC,
while the Elbrus glaciers between 4700 and 4900 m a.s.l. are
prone to surface melting. Snow accumulation measurements
from 1985 to 1988 showed total snow accumulation of 400–
600 mm w.e. a-1 with considerable wind-driven snow erosion
at the col of Elbrus (5300 m a.s.l.).
The summer atmospheric circulation pattern in the Cau-
casus is dominated by the subtropical high pressure to the
west and the Asian depression to the east. In winter, circula-
tion is aected by the western extension of the Siberian High
(Volodicheva 2002). The Caucasus is located in the southern
part of the vast Russian Plain and therefore bueted by the
unobstructed passage of cold air masses from the north.
High mountain ridges in the southern Caucasus deect air
owing from the west and southwest. The inuence of the
free atmosphere on the Elbrus glacier regime is greater than
local orographic eects as the glacier accumulation area lies
above main ridges.
Most part of the annual precipitation falls in the western
and southern parts of the Caucasus. For the southern slope
of the Caucasus, the amount of precipitation ranges from
3000–3200 mm a-1 in the west to 1000 mm a-1 in the east.
The proportion of winter precipitation (October–April) also
decreases eastward from more than 50 to 35–40% for the
northern Greater Caucasus and from 60–70 to 50–55% for the
southern slope (Rototaeva et al. 2006). The proportion of solid
precipitation increases with altitude and reaches 100% above
4000–4200 m.
Our research is focused on the southern slope of Elbrus,
from the Azau station (2330 m a.s.l.), along the Garabashi
Glacier (43°20´ N, 42°26´ E) to the summit (Fig. 1). The paper
discusses data obtained in 2017, 2016, and, also the data we
have obtained in previous years (Vasil’chuk et al., 2006, 2010;
Vasil’chuk and Chizhova 2010).
In terms of temperature, the 2015/16 season continued a
unique series of warm winters, which began in 2009/10. The
temperature anomaly was formed due to warm months at

174
the beginning (November) and the end of winter (February,
March). While the traditionally cold months (December, Janu-
ary) were slightly dierent from the long-year norm.
According to the amount of precipitation, the 2015/16
season was 18% below normal, and the winter maximum
precipitation was recorded in January. During the January
snowfall, 101.9 mm of precipitation fell, which was 36% of the
precipitation of the entire cold period (XI-III). The thickness
of the snow at the bottom of the valley during the second
decade of January increased from 30 cm to 72 cm (weather
station Terskol, 2141 m a.s.l.) and from 59 cm to 103 cm (Azau
weather station).
Winter 2016/17 was characterized by extremely low pre-
cipitation and long periods without precipitation, for exam-
ple, until January 26, 2017, snow fell only on 26 November.
The level of temperature drop with altitude (lapse rate) for
the southern slope of Elbrus is concerned to be 0.6 °C / 100 m.
This lapse rate was determined by comparison of automatic
weather station (installed on the western Elbrus plateau at
5115 m a.s.l.) record with measurements from the nearest
meteorological station (Mikhalenko et al. 2015).
METHODS
Snow was sampled on the south slope of Mt. Elbrus in
the middle of the snow accumulation period in January 2017,
February 2016, January 2001 and during snowmelt season in
July 1998 and August 2009. In 2017, fresh snow was sampled.
In 2016, the surface snow (1 Feb) and fresh snow (3 Feb) were
sampled, in 2001 and 2009 fresh snow was sampled. During
the ablation season of 1998, surface snow was sampled. The
sampling was performed at an altitude of about 1700 m (Fig.
2).
Samples of surface snow (from a depth of 0-15 cm)
were collected on 1 February 2016 (according to the Terskol
weather station, precipitation events were on 28 and 29 Jan-
uary). Samples of fresh snow collected on 3 February 2016
(from a depth of 0-15 cm) represent snow fell on 2 February
from morning till evening. According to the Terskol weather
station on 2 February, 9 mm of precipitation fell.
In January 2001 and August 2009, samples of just depos-
ited snow also have been collected within three hours after
snowfall at 0-10 cm depth of snow cover. Samples of melted
snow were collected at the Garabaschi glacier in July 1998.
GEOGRAPHY, ENVIRONMENT, SUSTAINABILITY 2020/01
Fig. 1. Space image of Elbrus from SPOT 7 satellite, August 20, 2016
Fig. 2. Sampling prole on the southern slope of Elbrus

175
Yurij Vasil’chuk, Julia Chizhova et al. A VARIATION OF STABLE ISOTOPE ...
In January 2017, samples of fresh snow were collected
within the range of 2300-3800 m a.s.l. On January 27 and 28,
in the valley and on the slope of Elbrus, the snow fallen on
26 January was sampled. On January 29, snow fell in the af-
ternoon and newly deposited snow was sampled on 30 Jan-
uary. All snow samples were taken from 0-10 cm depth of
snow cover. In the valley (2332 m a.s.l.) and at the slope (3345
m a.s.l.) snow pits had been excavated at 10 cm intervals.
Isotope ratios in snow of 2016, 2017 and 2009 were
measured by a Finnigan Delta-V continuous ow mass spec-
trometer in Stable Isotope Laboratory of Geographical De-
partment of Lomonosov Moscow State University. Concur-
rently, isotope composition of snow sampled in 2016, was
determined in Saint Petersburg State University Resource
center for Geo-Environmental Research and Modeling (GEO-
MODEL) by Picarro L-2120i. The dierences in measured δ18O
values for the same samples in two laboratories does not ex-
ceed ±0.3‰. Isotope composition of snow sampled in 2001
and 1998 was measured by W.Papesch in Research center
“Arsenal” in Seibersdorf, Austria.
Isotope data are expressed conventionally as δ-notion
(‰), representing a deviation in parts per thousand, relating
to the isotopic composition of V-SMOW (Vienna Standard
Mean Ocean Water). International standards V-SMOW2, GISP,
SLAP2 were used for the calibration. The measurement pre-
cision for δ18O values is ±0.1‰.
RESULTS
The δ18O - δ2H ratios for all snow samples (accumulation
and melt) are shown in Fig. 3. Most of them are very close to
the global meteoric water line.
Altitude isotope eect in fresh winter snow is clearly vis-
ible in 2016 at elevation up to 3000 m a.s.l and in 2001 at
elevation from 3000 to 4000 m a.s.l (Fig. 4, a). Inverse altitude
eect was observed in fresh snow sampled in 2016 above
3000 m a.s.l and in August 2009 (Fig. 4, b).
The values of d-excess (dexc) in fresh snow have season-
al variations increasing in summer (Table 1). The dexc values
depend on the relative humidity of the air masses at their
oceanic origin (Merlivat and Jouzel 1979). The lower dexc val-
ues of precipitation in the northern hemisphere during the
summer months correspond with the higher relative air hu-
midity which relates to the SST in the oceanic source regions
of the air masses concerned. In the Chinese Tien Shan, high
dexc values were noted during the winter months when pre-
Fig. 3. The δ18O - δ2H plot for all snow samples: 1998, 2001, 2009, 2016, 2017
Fig. 4. The δ18O values in snow cover of Elbrus Mountain in winter (a) and summer season (b)

176
GEOGRAPHY, ENVIRONMENT, SUSTAINABILITY 2020/01
cipitation fell at low temperatures and low relative humidi-
ty (Pang et al. 2011). On the contrary, the higher dexc values
during the winter months are caused by the lower relative
humidity at the oceanic source regions. The inverse trend
for dexc values in summer precipitation may occur in regions
where the atmospheric water vapor dominates due to mois-
ture evaporation from continental basins (Schotterer et al.
1993; Schotterer et al. 1997).
We consider separately the surface snow (which lay af-
ter falling out for some time and was subjected to various
processes: re-deposition, sublimation, melting, drifting, etc.)
and fresh newly deposited snow, which was sampled either
immediately after snowfall or the next day after.
Newly deposited (fresh) snow
In fresh snow sampled on 27 and 28 January 2017, the
δ18O values vary from –24.84 to –34.46‰, the δ2H from –173.2
to –247.9‰ (Table 2). Regardless of the date of selection, all
samples are in the altitude range of 2256-3850 m a.s.l. Prac-
tically, there is no clear relationship between the δ18O and
δ2H values and altitude (Fig. 5). However, some weak trend
to decreasing δ18O values with altitude can be identied by
calculating the dierence between isotope content at 2256
m a.s.l. and 3850 m a.s.l. It gives the gradient to be −0.32‰
δ18O/100 m.
On 3 February 2016, the δ18O values increased from
−34.5‰ to −25.5‰ in fresh snow between 2287 and 3836
m a.s.l., the lowest δ18O values were obtained near 3000 m
a.s.l. (Fig. 6). It was found that there is a clear inverse altitudi-
nal isotope eect between 4000 and 3000 a.s.l. with a gradi-
ent of δ18O = +1.04‰/100 m (Table 2). Below 3000 m a.s.l.,
the δ18O and δ2H values distributed randomly which could
be attributed to the lower boundary of air mass or turbulent
mixing inside of it.
In August 2009, fresh snow showed weak positive iso-
tope trend with altitude with a low statistical signicance
(Fig. 7).
In 2001, the altitudinal isotope eect has been observed
above 3000 m in fresh snow with gradient of δ18O –1.3‰/100
m and δ2H –11.1‰/100 m (at 3100 m δ18O = –17.81‰, δ2H
= –128.1‰, at 3900 m δ18O = –28.24‰, δ2H = –217.1‰, see
Fig. 6).
Simultaneous temperature measurements on the
southern slope of Elbrus in the altitude range of 2355−3853
m showed temperature drop with altitude for dierent
types of weather in the 2016/17 season (Table 3).
Table 1. Deuterium excess of snow cover of Elbrus Mountain
Year Type of snow
dexc, ‰
mean max min
1998 Summer melted 11 15 7
2001 Winter fresh 11 14 9
2009 Summer fresh 22 32 18
2016 Winter fresh 12 22 2
2017 Winter fresh 24 33 17
Fig. 5. The altitudinal eect on δ18O, δ2Н and dexc for fresh snow in 27 January 2017

177
Yurij Vasil’chuk, Julia Chizhova et al. A VARIATION OF STABLE ISOTOPE ...
Table 2. The altitudinal distribution of δ18O and δ2H values in fresh snow on Elbrus in 2016 and 2017
Sample ID Height, m δ18O, ‰ ∆ δ18O, ‰/100 m δ2H, ‰ dexc, ‰
03.02.2016
E19 c 3836 –25.5

+1.04
–191 12.68
E20 c 3747 –29.2 –224 9.63
E21 c 3705 –27.7 –209 12.04
E22 c 3588 –31.1 –243 6.45
E23 c 3457 –34.4 –260 15.59
E24 c 3403 –32.1 –242 14.87
E26 c 3351 –31.3 –237 12.96
E27 c 3307 –33.9 –257 14.51
E28 c 3255 –32.8 –253 10.02
E29 c 3197 –34.5 –266 10.13
E30 3142 –33.3 –253 13.43
E31 3064 –33.5 –259 8.98
E32 2978 –32.2
Not pronounced
–253 5.18
E35 2353 –31.8 –242 12.11
E34 2321 –32.1 –242 14.71
E33 2287 –31.6 –241 11.32
04.02.2016
E36 с 2908 –32.2
Not pronounced
–252 6.12
E37 с 2462 –27.0 –209 6.51
E38 с 2884 –32.6 –247 14.26
E39 с 2548 –31.2 –236 13.57
E40 с 2872 –29.7 –236 1.80
E41 с 2796 –29.2 –222 11.61
E42 с 2744 –28.7 –219 10.83
E43 с 2665 –31.3 –241 9.12
27.01.2017
E1-2017 3850 –31.28
Not pronounced
–225,9 24.3
E7-2017 3820 –30.65 –220 25.2
E2-2017 3764 –32.12 –228 28.96
E9-2017 3716 –33.97
–0.32
–241.6 30.16
E3-2017 3598 –32.47 –230.8 28.96
E4-2017 3468 –30.47 –216.5 27.26
E15-2017 3443 –34.46 –247.9 27.78
E5-2017 3400 –29.15 –213 20.2
E8-2017 3351 –32.31 –225.2 33.28
E6-2017 3205 –32.31 –230.8 27.68
E16-2017 3130 –30.61 –224.5 20.38
E10-2017 2931 –32.02 –236.8 19.36
E11-2017 2865 –24.84 –173.2 25.52
E13-2017 2579 –30.94 –220.3 27.22
E14-2017 2454 –31.24 –232.9 17.02
E18-2017 2256 –29.28 –212.7 21.54
E19-2017 2145 –15.63 –102.7 22.34

178
These values mean that for the snow samples of 2001, in
which the altitude isotope eect is pronounced (from 2900
to 3900 m a.s.l.), the relationship coecient δ18O with T is in
the range from 0.55 ‰/˚С to 0.76 ‰/˚С (based on Table 3
data for dierent types of weather). This corresponds to the
Rayleigh model of equilibrium isotope fractionation.
The decrease of dexc values with altitude was revealed
(see Fig 6). Such decreasing dexc values during snowfall con-
tradicts other model calculations (Jouzel and Merlivat 1984;
Ciais and Jouzel 1991) and eld observations (Vasil’chuk et
al. 2005).
Surface snow
Snow sampled on February 1, 2016, in the range of 1900
m − 4100 m a.s.l. is characterized by insignicant isotope vari-
ations (see Fig. 7). The possible reasons are: 1) the formation of
isotope composition of snow at single condensation level from
extensive cloud; 2) the initial isotope signal of the snow may
GEOGRAPHY, ENVIRONMENT, SUSTAINABILITY 2020/01
Fig. 6. The altitudinal eect on δ18O, δ2Н and dexc for fresh snow in 8 February 2001 and 3 February 2016
Fig. 7. The altitudinal eect on δ18O, δ2Н and dexc for fresh snow in August, 2009 and for surface snow 1 February, 2016

179
Yurij Vasil’chuk, Julia Chizhova et al. A VARIATION OF STABLE ISOTOPE ...
be modied by processes of drifting or wind erosion. In the ab-
lation season of 1998, the residual surface melted snow had
the highest δ18O values from −6.82 to −8.79‰ and δ2H from
−41.9 to −57.0‰ (see Fig. 4, b). That probably was a result of
spring-summer snow accumulation modied by sublimation
and partial melting. The lower value at 3780 m a.s.l. indicates
partial melting of surface snow and exposure of winter snow.
The absence of altitudinal isotope eect can be explained
by the fact that snow-bearing air masses undergo no small-
scale orographic uplift and secondly that the source and the
trajectory of air masses are essential to the average isotopic
content (Moran et al. 2007).
Snow pits
The mean values of δ18O for two snow pits in January 2017
at 2332 m and 3345 m a.s.l. were –26.4 ‰, –24.8 ‰ and the
values for δ2H were –189.7 ‰, –174.8 ‰, respectively. While
the mean δ18O and δ2H values in snow pit at a lower altitude
are more negative than the values at a higher altitude (Fig. 8).
In the pit at 2332 m, the upper horizon is formed by snow with
low values of δ18O (–29.4 ‰) and δ2H (–215.4 ‰), this is clear-
ly freshly fallen January snow, in other snow horizons the δ18O
and δ2H values are close to a uniform.
Similar values of δ18O and δ2H were obtained in the mid-
dle snow horizons at 3345 m a.s.l., while the lower horizon
here is characterized by relatively high values (see Fig. 8), in-
dicating the accumulation and preservation of snow, which
was fallen most probably in autumn.
Interpretation
In fresh snow in February 2016, the most negative val-
ues of δ18O from −31.3 to −34.4‰ in the range of 3064–
3457 m a.s.l. (Table 2) are extreme for Elbrus, especially for
elevation below 4000 m a.s.l. Snow pit and rn core isotope
records obtained at 5115 m a.s.l. (Kutuzov et al. 2013) show
a clear season variation from −27 ‰ to −5.5 ‰ for δ18O val-
ues. Extremely negative isotope values in fresh snow of 2016
may be explained by drying of the air mass. The evolution
of the isotope composition of water vapor during conden-
sation and rainout from an idealized air mass is commonly
modeled as a Rayleigh distillation process. The late stages of
rainout are associated with rapid decreases of δ18O values
in precipitation and in vapor. The rate of decrease of δ18O
values also increases exponentially as the air mass dries out,
and is greater at lower temperatures (Moran et al. 2007).
Table 3. Measured air temperature on the southern slope of Elbrus in 2017
Date and type of the
weather
Height a.s.l.
30/01/2017
Cloudy with clearings,
overhead fog
31/01/20017
Clear, little
cloudy
4/02/2017
Clear, in the
morning cloudy
5/02/2017
Cloudy with clearings, the bottom
of the sun, above the fog
2355 –15 –18 –4 –2
2934 –22 –21 –7 –8
3465 –27 –28 –13 –12
3853 –23 –26 –15 –14
calculated lapse rate
˚C/100 m –0.53 –0.53 –0.734 –0.80
Fig. 8. The values of δ18O, δ2H and dexc in snow pits at 2332 and 3345 m a.s.l.

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GEOGRAPHY, ENVIRONMENT, SUSTAINABILITY 2020/01
In any case, we can not ignore the empirical data obtained
for snow on 3 February, even if the isotope values distribu-
tion was not described by any model.
The formation of an altitude isotopic eect is not always
associated with local conditions like a windward / leeward
slope, temperature, etc. The absence of altitude eect is often
explained by the fact that air masses do not follow the oro-
graphic uplift and, secondly, the source and trajectories of air
masses, that could change pretty fast, are both important for
the formation of isotope composition.
Moore et al. (2016) investigated the importance of non-
local processes through the analysis of the synoptic scale
circulation during a snowfall event at the summit of Mount
Wrangell in south-central Alaska. During this event, there was
over a 1-day period in which the local temperature was ap-
proximately constant, a change in δ18O values that exceeded
half that normally seen to occur between summer and winter
in the region. It may be suggested that a change in the source
region for the snow that fell on Mount Wrangell during the
event from the subtropical eastern Pacic to northeastern
Asia.
In order to explain isotope signal in the sow collected on
the 3rd of February, we suppose a simultaneous coming of
one air mass to the mountain slope, but by two ways. Back-
ward air masses trajectories to Mt. Elbrus are provided by
NOAA using the HYSPLIT model (Draxler and Rolph 2011), cal-
culated for the 3rd of February at 3000 and 5000 m showed
one source and one path of moisture from the north. The most
negative δ18O and δ2H values corresponded to 3064–3457 m
a.s.l. range. One of the reasons for this distribution of δ18O and
δ2H values in snow is the removal of a part of the snow from
the summit zone to a height of 3000 m. In this case, snow
with low δ18O and δ2H values, deposited on summit is blown
downward, forming a reverse altitude isotope eect. Another
reason is that the altitude of 3000 m corresponds to the zone
of maximum accumulation. Progressive precipitation leads to
strong isotopic depletion of the remaining vapor and the last
precipitation. It is obvious that the inverse high-altitude iso-
tope eect is associated with these very negative values at an
altitude of about 3000 m.
In fresh snow sampled in 2017 with a weakly decreasing
of δ18O and δ2H values with altitude, there is also a very slight
increase of dexc. The main feature of the isotope signature of
snow in 2017 is high dexc values reaching 33‰ (see Table 1,
Table 2). Backward HYSPLIT trajectories to Mt. Elbrus for the
26th of January 2017 at 3000 and 5000 m showed the source
of moisture was the Mediterranean area. It is known that this
region during the winter months due to low relative humidity
over the sea is a source of precipitation with high deuterium
excess (Gat and Carmi 1970).
In fresh snow sampled in 2001, there was a “classical” alti-
tudinal isotope eect in precipitation due to orographic uplift
of air masses and the related decrease in the condensation
temperature (see Fig. 6).
When precipitation falls from air masses as they traverse
topographic barriers, continued Rayleigh distillation on the
lee slope should indeed produce an inverse relationship with
altitude-lighter isotopic ratios with decreasing altitude. This
would suggest a systematic altitudinal relationship that is
the opposite of that which is observed on windward slopes,
but an inverse relationship of this type is not well established
or widely reported.
Poage and Chamberlain (2001) provide a compilation of
observed δ18O-elevation gradients from 68 dierent studies
worldwide, with only two of these studies reporting δ18O
depletion of precipitation with altitude. Ambiguous or in-
verse δ18O-elevation relationships have been reported from
eastern (lee) slopes in Sierra Nevada (Friedman and Smith
1970) and the Canadian Rockies (Grasby and Lepitski 2002).
Complex altitudinal relationships are also evident in high al-
pine snow samples (Niewodnizański et al. 1981). This study
indicates the necessity to further study the isotope variabil-
ity of the snow cover to predict the isotopic composition of
snowmelt water and to better understand the accumulation
processes and the sources of snow in high mountains.
CONCLUSIONS
The results suggest that δ18O-elevation gradients in fresh
snow on south slope of Elbrus Mountain have similar values
but opposite trends in dierent years and seasons. Above
3000 m in 2001, the δ18O values decreased with altitude by
–1.3 ‰/100 m (–11,1‰ δ2H /100 m), in 2016, the δ18O values
increased with altitude by +1.04 ‰ /100 m (+8.76 ‰ δ2H
/100 m).
In 2017, the relationship between the values of δ18O and
δ2H with the altitude of the terrain is not clearly pronounced
with a weakly decreasing δ18O values in an altitude range
of 2256–3716 m a.s.l., there is also a very slight increase of
dexc. Such an uneven distribution of the isotope composition
of snow with altitude in dierent seasons most likely is ex-
plained by various mechanisms of snow deposition – oro-
graphic uplift of the air mass along the slope or over-climb-
ing through the main Caucasian ridge and considerable drift
of dry snow on the slope.
Below 3000 m, the disruption of δ18O-elevation gradi-
ents has been attributed to post-depositional altering, wind
movement, turbulent mixing of air masses or simultaneous
coming of an air mass to the slope.
ACKNOWLEDGEMENTS
Researches are nancially supported by Russian Founda-
tion for Basic Research (grantsRFBR № 16-05-00977 eld re-
search, 18-05-60272, isotope analyses and 18-05-60021, data
compilation).

181
Yurij Vasil’chuk, Julia Chizhova et al. A VARIATION OF STABLE ISOTOPE ...
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Received on May 31th, 2018 Accepted on January 21th, 2020