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Do contemporary (1980–2015) emissions determine the elemental carbon deposition trend at Holtedahlfonna glacier, Svalbard?

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The climate impact of black carbon (BC) is notably amplified in the Arctic by its deposition, which causes albedo decrease and subsequent earlier snow and ice spring melt. To comprehensively assess the climate impact of BC in the Arctic, information on both atmospheric BC concentrations and deposition is essential. Currently, Arctic BC deposition data are very scarce, while atmospheric BC concentrations have been shown to generally decrease since the 1990s. However, a 300-year Svalbard ice core showed a distinct increase in EC (elemental carbon, proxy for BC) deposition from 1970 to 2004 contradicting atmospheric measurements and modelling studies. Here, our objective was to decipher whether this increase has continued in the 21st century and to investigate the drivers of the observed EC deposition trends. For this, a shallow firn core was collected from the same Svalbard glacier, and a regional-to-meso-scale chemical transport model (SILAM) was run from 1980 to 2015. The ice and firn core data indicate peaking EC deposition values at the end of the 1990s and lower values thereafter. The modelled BC deposition results generally support the observed glacier EC variations. However, the ice and firn core results clearly deviate from both measured and modelled atmospheric BC concentration trends, and the modelled BC deposition trend shows variations seemingly independent from BC emission or atmospheric BC concentration trends. Furthermore, according to the model ca. 99 % BC mass is wet-deposited at this Svalbard glacier, indicating that meteorological processes such as precipitation and scavenging efficiency have most likely a stronger influence on the BC deposition trend than BC emission or atmospheric concentration trends. BC emission source sectors contribute differently to the modelled atmospheric BC concentrations and BC deposition, which further supports our conclusion that different processes affect atmospheric BC concentration and deposition trends. Consequently, Arctic BC deposition trends should not directly be inferred based on atmospheric BC measurements, and more observational BC deposition data are required to assess the climate impact of BC in Arctic snow.
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Atmos. Chem. Phys., 17, 12779–12795, 2017
https://doi.org/10.5194/acp-17-12779-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Do contemporary (1980–2015) emissions determine the elemental
carbon deposition trend at Holtedahlfonna glacier, Svalbard?
Meri M. Ruppel1, Joana Soares2,3, Jean-Charles Gallet4, Elisabeth Isaksson4, Tõnu Martma5, Jonas Svensson1,2,
Jack Kohler4, Christina A. Pedersen4, Sirkku Manninen1, Atte Korhola1, and Johan Ström6
1Department of Environmental Sciences, University of Helsinki, Helsinki, 00790, Finland
2Finnish Meteorological Institute (FMI), Helsinki, 00560, Finland
3Air Quality Research Division, Environment and Climate Change Canada, Toronto, M3H 5T4, Canada
4Norwegian Polar Institute, Tromsø, 9296, Norway
5Department of Geology, Tallinn University of Technology, Tallinn, 19086, Estonia
6Department of Environmental Science and Analytical Chemistry ACES (Atmospheric Science Unit), Stockholm University,
Stockholm, 11418, Sweden
Correspondence to: Meri M. Ruppel (meri.ruppel@helsinki.fi)
Received: 20 April 2017 – Discussion started: 5 May 2017
Revised: 1 September 2017 – Accepted: 7 September 2017 – Published: 26 October 2017
Abstract. The climate impact of black carbon (BC) is no-
tably amplified in the Arctic by its deposition, which causes
albedo decrease and subsequent earlier snow and ice spring
melt. To comprehensively assess the climate impact of BC in
the Arctic, information on both atmospheric BC concentra-
tions and deposition is essential. Currently, Arctic BC de-
position data are very scarce, while atmospheric BC con-
centrations have been shown to generally decrease since the
1990s. However, a 300-year Svalbard ice core showed a dis-
tinct increase in EC (elemental carbon, proxy for BC) depo-
sition from 1970 to 2004 contradicting atmospheric measure-
ments and modelling studies. Here, our objective was to de-
cipher whether this increase has continued in the 21st century
and to investigate the drivers of the observed EC deposition
trends. For this, a shallow firn core was collected from the
same Svalbard glacier, and a regional-to-meso-scale chem-
ical transport model (SILAM) was run from 1980 to 2015.
The ice and firn core data indicate peaking EC deposition
values at the end of the 1990s and lower values thereafter.
The modelled BC deposition results generally support the
observed glacier EC variations. However, the ice and firn
core results clearly deviate from both measured and mod-
elled atmospheric BC concentration trends, and the modelled
BC deposition trend shows variations seemingly independent
from BC emission or atmospheric BC concentration trends.
Furthermore, according to the model ca. 99 % BC mass is
wet-deposited at this Svalbard glacier, indicating that meteo-
rological processes such as precipitation and scavenging effi-
ciency have most likely a stronger influence on the BC depo-
sition trend than BC emission or atmospheric concentration
trends. BC emission source sectors contribute differently to
the modelled atmospheric BC concentrations and BC deposi-
tion, which further supports our conclusion that different pro-
cesses affect atmospheric BC concentration and deposition
trends. Consequently, Arctic BC deposition trends should not
directly be inferred based on atmospheric BC measurements,
and more observational BC deposition data are required to
assess the climate impact of BC in Arctic snow.
1 Introduction
Black carbon (BC) is a carbonaceous fine particle with strong
light-absorbing ability. It is produced by natural and anthro-
pogenic incomplete combustion of biomass and fossil fuels
and may be transported with prevailing winds over thousands
of kilometres from its emission sources (e.g. Ramanathan
and Carmichael, 2008; Bond et al., 2013). It poses a global
environmental threat by warming the atmosphere, but the cli-
mate impacts of BC are amplified in the Arctic, where its de-
position on snow and ice decreases surface reflectance and
hastens snow and ice melt, which further decreases the re-
Published by Copernicus Publications on behalf of the European Geosciences Union.
12780 M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends?
flectivity (e.g. Hansen and Nazarenko, 2004). Globally, BC is
the second most important climate warming agent after car-
bon dioxide. However, in the Arctic, due to the snow–albedo
feedback, the effect of BC in the observed warming and melt-
ing may exceed that of greenhouse gases (e.g. Flanner et al.,
2007, 2009; Bond et al., 2013).
Atmospheric BC concentrations have been monitored in
the Arctic starting since 1989 at Alert (Canada), Barrow
(USA) and later at Zeppelin (Ny-Ålesund, Norway), and
the observations show a 40% decrease from 1990 to 2009
(Sharma et al., 2013). Furthermore, measurements from
northern Finland showed a 78 % decrease in atmospheric BC
concentrations between 1971 and 2011 (Dutkiewicz et al.,
2014). This observed decrease is mostly attributed to the fall
of the USSR and a resulting decrease in BC emissions in
major source areas of Arctic BC (e.g. Sharma et al., 2013).
However, atmospheric observations reflect the effect of BC
on Arctic climate only partially, as the climate effect of BC
deposited on high-reflectance snow and ice surfaces is no-
tably stronger than of atmospheric BC (Flanner et al., 2007,
2009; Bond et al., 2013). As 85–90 % of BC is suggested to
be wet-deposited in the Arctic (Wang et al., 2011), and the
BC proportion bound by precipitation is mostly not recorded
by atmospheric measurements, the BC emission and atmo-
spheric BC concentration trends may not reliably represent
the BC deposition trend. Therefore, to comprehensively as-
sess the effects of BC in Arctic climate change, observations
on its deposition rate and trend in the area are also essential.
Ice cores represent a valuable means to study BC deposi-
tion as they accumulate direct evidence of contaminant de-
position in chronological order, potentially for hundreds to
thousands of years. Ice core records are irreplaceable when
evaluating e.g. contemporary atmospheric or snow BC con-
centration variations in the context of past BC variations
and when evaluating the role of these variations for the ob-
served climate change in the Arctic and beyond. Despite
the importance of ice core records in deciphering the role
of BC in Arctic climate change, relatively few records ex-
ist at present. Four continuous BC ice core records covering
ca. 1750 to 2013 have been published from Greenland (Mc-
Connell et al., 2007; McConnell and Edwards, 2008; Mc-
Connell, 2010; Keegan et al., 2014) and one 300-year record
(1700 to 2004) from Svalbard (Ruppel et al., 2014). The
high-elevation Greenland records indicate a BC deposition
peak around 1910 followed by rapidly decreasing deposition
until 1950 and more or less stable, almost preindustrial val-
ues until the present (McConnell, 2010). The Svalbard ice
core clearly concurs with the Greenland records for the early
20th century but unexpectedly shows a pronounced increase
in BC concentrations and deposition from 1970 to the top
of the core in 2004 (Ruppel et al., 2014). The reasons for
the observed post-1970 BC deposition increase in Svalbard
– while at the same time Greenland ice cores, atmospheric
measurements (e.g. Sharma et al., 2013) and model results
(e.g. Koch et al., 2011) suggest decreasing BC values – was
left partly unresolved (Ruppel et al., 2014). Increasing flaring
emissions from northern Russia in the Barents Sea area that
do not reach the Greenland ice coring sites due to restricted
isentropic uplift in the Arctic, and potentially increasing wet-
scavenging efficiency due to increasing temperatures partic-
ularly around Svalbard, were the leading hypotheses (Ruppel
et al., 2014). A similar rapid increase in BC fluxes between
ca. 1970 and 2013 was also observed in two lake sediment
records from northern Finland (Ruppel et al., 2015).
The increasing BC deposition on the Svalbard glacier has
significant effects on the radiative budget of this site and
concurs with substantially increased summer melting of the
glacier since the 1980s (Ruppel et al., 2014). The increased
melt of the glacier is better explained by the combination of
observed increasing summer temperatures and the increasing
BC concentrations than by increasing temperatures alone. To
estimate the extent of the climatic implications suggested in
Ruppel et al. (2014) it is essential to solve whether the ob-
served increasing BC deposition trend in Svalbard since 1970
can be corroborated with other data. Furthermore, it is nec-
essary to thoroughly assess the BC sources responsible and
the deposition processes associated to the observed increase
because these may affect also other parts of the Arctic.
Here, our objective is to resolve what the BC deposition
trend has been during the last 10 years on the previously
studied Svalbard glacier, Holtedahlfonna. For this, a new
14.7 m deep firn core and a 2.5 m thick accumulated winter–
spring snow profile were collected from Holtedahlfonna in
April 2015. BC was analysed from the samples as elemen-
tal carbon (EC) with the same methodology (thermal–optical
with the EUSAAR 2 protocol) as in Ruppel et al. (2014).
In addition, the source of the BC deposited at the glacier
is investigated using a meso-to-global-scale chemical trans-
port model System for Integrated modeLling of Atmospheric
composition Model (SILAM; Sofiev et al., 2012). The results
may have significant implications for the comprehensive as-
sessment of the impact of BC in the recent past, present and
future Arctic climate system.
2 Material and methods
2.1 Site description and field sampling
Svalbard is an archipelago located in the Arctic Ocean
(Fig. 1). It has relatively mild climate despite its location
at high latitudes due to an intrusion of the North Atlantic
current bordering western Svalbard and its location in the
pathway of both Arctic and North Atlantic cyclones. Sval-
bard is covered up to 60% by glaciers, of which the major-
ity have retreated during the last 15–40 years (Nuth et al.,
2010), and even the glaciers situated at highest elevation (ca.
1200 m a.s.l.) experience frequent surface melt in the sum-
mer (e.g. Beaudon et al., 2013).
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M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends? 12781
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Figure 1. Map of Svalbard and the location of study sites on the
Holtedahlfonna glacier. The inset presents an aerial satellite image
of the Holtedahlfonna glacier in summer. The 300-year ice (2005)
and firn (2015) core study sites are indicated by red circles.
Holtedahlfonna is a ca. 300 km2ice field in western Sval-
bard, located 40 km north-east of the Ny-Ålesund research
station (Fig. 1). A 125 m deep ice core was drilled in
April 2005 at 1150 m elevation, at a saddle point of a moun-
tain ridge at the edge of Holtedahlfonna (Fig. 1; 7908.150N,
1316.200E). This coring location was selected based on the
current knowledge of the subglacial bedrock topography. The
ice core was estimated to cover ca. 300 years, and EC was
analysed from the inner core section (Ruppel et al., 2014).
The EC analysis revealed an unexpected increase in the Arc-
tic from 1970 to 2004 (i.e. the top of the core). To confirm
the observed trend and to decipher whether the trend had
continued after 2004, a new 14.7 m deep firn core was col-
lected on 19 April 2015 from the same glacier, at 1120m
elevation (7908.4240N, 1323.6390E). The new coring site
was located ca. 2.8 km south-east from the 2005 coring site
(Fig. 1) in the vicinity of a mass-balance measurement stake,
and thus annual snow accumulation measurements are avail-
able from this site since 2003. Before drilling, the top 80 cm
of the snow pack were removed to obtain a hard surface to
drill. The core was collected with a PICO drill, and a depth
of 14.7 m below the snow surface was reached. A combina-
tion of time constraint and type of drill did not permit drilling
deeper. The firn was retrieved in ca. 60–100 cm sections and
was immediately packed into labelled plastic bags.
In addition, a 2.53 m deep snow pit was dug on 21 April
ca. 15 m away from the firn coring site to study the top snow
layers missed by the firn core and the annual EC variation
in more detail. The snow pit was dug down to the previous
summer surface that was identified both by a (the only) hard
layer in the snow pack and the snow accumulation data re-
trieved from the mass-balance measurements at the site. The
snow column thus covers the accumulated snow from the end
of summer 2014 to April 2015. The snow was first excavated
and snow physical properties were recorded, particularly the
snow stratigraphy, which allowed the identification of differ-
ent layering in the snow pack. In total, 13 samples were col-
lected into whirl-pack bags, resulting in on average a 20cm
vertical resolution for EC measurements in snow. The firn
core and snow samples were stored frozen and transported to
the Norwegian Polar Institute (NPI), Tromsø, Norway.
The firn core was cut in a freezer laboratory (22 C) us-
ing a thin blade band saw. Each vertical ice core section was
split to subsamples assigned to oxygen and hydrogen isotope
ratio and EC analyses. The outer 1–2 cm layer of the firn core
was removed and the isotope and EC samples were cut from
the inner part of the firn core protected from possible con-
tamination during drilling, packing and handling until dis-
tributed into clean sample vials. As the EC concentration of
the firn samples was expected to be quite low for the thermal–
optical method to detect, the sample sizes for EC measure-
ments were kept relatively large. The core was divided into
14 vertical subsamples for EC measurements of ca. 1 m to-
tal length each and an average horizontal cross section of 4.2
by 4.5 cm, equal to an average cross-sectional area of 19 cm2
(±2 cm2). The subsamples generated between 0.9 and 1.2 L
meltwater.
2.2 Filtering and EC analysis
To ensure comparability, the filtering and EC analysis of
the firn core and snow samples were performed in the
same facilities and with same instruments as in Ruppel
et al. (2014), which followed the original procedure of
Forsström et al. (2009). The frozen samples were melted
and immediately filtered through precombusted (at 800 C
for 4 h) quartz fibre filters (Munktell) in a glass filtering sys-
tem. All parts of the filtering system were cleaned between
each sample using distilled water and a brush. Blanks (five
samples) were prepared to check for possible contamination
in the filtering system. The filters were allowed to dry in in-
dividual petri dish containers in a clean cupboard and subse-
quently individually wrapped into aluminium foil and stored
in a refrigerator (+6–8 C) before analysis.
The filters were analysed for EC using a thermal–optical
method (Sunset Laboratory Inc., Forest Grove, USA; Birch
and Cary, 1996) with the latest recommended thermal se-
quence EUSAAR_2 (Cavalli et al., 2010) at Stockholm Uni-
versity. In the first stage, the method separates organic and
carbonate carbon from the filters under increasing tempera-
ture steps in a helium atmosphere, while EC evolves from the
filters in the second stage under a helium–oxygen atmosphere
at temperatures reaching 850 C. During analysis, the trans-
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12782 M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends?
0 100 200 300 400 500 600 700 800 900
-25
-20
-15
-10
-5
0
-160
-120
-80
-40 200520072009201120132014
2
δ H
18
δ O
Cumulative snow water equivalent accumulation (cm)
September of year
2012 2010 2008 2006
Figure 2. Holtedahlfonna firn core isotope and measured mass balance inferred dating. The red and blue curves present the hydrogen and
oxygen isotope profiles for the firn core. The dashed lines indicate the September layers of the firn core against the firn depth in cumulative
snow water equivalent centimetres. These data are based on snow accumulation rate (mass balance) measurement on a nearby stake. Please
see text for more details.
mittance of the filter is monitored using laser light, which
allows for optical correction of charring, i.e. potential py-
rolysis of organic carbon to EC during the analysis (Cavalli
et al., 2010). All blanks showed EC concentrations well be-
low detection limit of the analysis method (0.2 ECµgcm2).
The used methodology includes uncertainties that are de-
scribed in more detail in Ruppel et al. (2014). In short, in liq-
uid samples (i.e. melted snow and ice) smallest EC particles
may go through the filter (e.g. Torres et al., 2014), leading
to a quantified undercatch of ca. 22 % for the used filtering
set-up (Forsström et al., 2013). In addition, from each filter
sample (11.34 cm2) only a small punch (1.5 cm2) is anal-
ysed for EC. To evaluate the uncertainties caused by this sub-
sampling, triplicate analyses were prepared for five ice core
samples. These measurements (Fig. 4c) showed an average
relative SD of 8.5% (range of relative SD=5.3–13.7 %),
which is smaller than reported e.g. in Ruppel et al. (2014;
19.6 % average relative SD). Combined, i.e. added together
in quadrature, these error sources cause a ca. 23.6 % uncer-
tainty in our current EC measurements.
2.3 Dating of firn core
The 14.7 m firn core was dated by preparing a composite esti-
mate based on annual layer counting using the seasonal vari-
ability in the oxygen (δ18O) and hydrogen (δ2H) stratigraphy
in combination with snow density and mass-balance mea-
surements (stake 10) next to the coring site recorded since
2003. For the oxygen and hydrogen isotope analysis the core
was sampled at 5 cm vertical resolution following methods
described in Divine et al. (2011). The isotope analyses were
performed at Tallinn University of Technology using a Pi-
carro L2120-i water isotope analyser with a high-precision
AO211 vaporizer. The results were calibrated to VSMOW
scale. Reproducibility of the δ18O and δ2H measurements
was ±0.1 and ±1 ‰, respectively.
There are very pronounced variations with large seasonal
amplitudes in the water isotope records in the uppermost
2 m of the core assumed to be due to different atmospheric
sources of precipitate. These annual variations gradually get
smoothed out due to diffusion during the firnification process
(Fig. 2), rendering the distinction between years more diffi-
cult with increasing depth. Therefore, supporting data from
the mass-balance stake are useful for dating. Stake 10 has
been visited and maintained regularly since 2002 and thus
an annual mass balance of the study site is available from
2003. By combining the density and depth data from the firn
core, the snow water equivalent along the core profile could
be obtained and was compared with the mass-balance (snow
water equivalent accumulation) data measured at the stake
since 2003. Thereby, the limit of years (September measure-
ment points at the stake) could be determined as a function of
depth, and subsequently the core could be dated. The density
and water isotope inferred dating of the core match well with
the mass-balance inferred limits of years (Fig. 2).
2.4 Atmospheric modelling
SILAM (Sofiev et al., 2008), a model developed by the
Finnish Meteorological Institute, was run for a simulation
between 1980 and 2015 to study BC deposition variations
and the contribution of different sources of BC deposited
at Holtedahlfonna. SILAM is a meso-to-global-scale chem-
ical transport model. For this study, the model was driven
Atmos. Chem. Phys., 17, 12779–12795, 2017 www.atmos-chem-phys.net/17/12779/2017/
M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends? 12783
1980 1990 2000 2010
101
102
103
104
Year
Mg BC yr −1
(a) Global BC emissions
1980 1990 2000 2010
100
101
102
103
104
Year
Mg BC yr−1
(b) BC emissions north of 40° N
awb
dom
ene
fire
flr
ind
ships
tra
wst
All
Total anthropogenic
Figure 3. Temporal trend of BC emissions by sector from 1980 to 2015: (a) globally and (b) north of 40N. The emission sectors are as
follows: all indicates all anthropogenic and natural sources combined, total anthropogenic is all anthropogenic sources, awb is agricultural
waste burning, dom is domestic, ene is energy production, fire is natural fires, flr is flaring, ind is industry, ships is shipping, tra is transport
and wst is waste incineration. Anthropogenic MACCity BC emissions are from Granier et al. (2011), ECLIPSE flaring emissions from
Klimont et al. (2013) and natural fire emissions from Lamarque et al. (2010). Note the logarithmic yaxes.
by ERA-Interim (Dee et al., 2011) meteorology and by
global MACCity anthropogenic BC emissions (Granier et al.,
2011) updated with ECLIPSE emission data set for flaring
(Klimont et al., 2013) and natural fire (open biomass burn-
ing) emissions (Lamarque et al., 2010) shown in Fig. 3. Gen-
erally, BC emissions north of 40N are considered signif-
icant for the Arctic (AMAP, 2011). Unfortunately, to our
knowledge, there is no single continuous data source of nat-
ural fire BC emissions from 1980 to 2015. The Lamarque
et al. (2010) data set we used here is based on estimated
burned land area and extends until the year 2008. Between
2008 and 2015 constant emissions of 2008 were used. Kaiser
et al. (2012) and Soares et al. (2015) have shown that the
emission data estimated by burned area data tend to be un-
derestimated. An alternative data set of natural fire BC emis-
sions, which is considered more reliable, is based on satellite
images, IS4FIIRES (Soares et al., 2015). However, the satel-
lite emission data are available only since 2003 and show
considerably higher values, which would cause a step change
in the emissions if the data sets were combined. As our objec-
tive is to examine trends for 1980 to 2015, it is more reason-
able to use the longer Lamarque et al. (2010) data set in our
simulations. The total global BC emissions have increased in
the study period while north of 40N they have decreased
(Fig. 3). Svalbard receives atmospheric transportation domi-
nantly from Eurasia (e.g. AMAP, 2011), and anthropogenic
BC emissions from this region have decreased in the study
period while natural fire emissions have increased (e.g. Bond
et al., 2007; Lamarque et al., 2010).
The model was run through the period between 1980 and
2015 with 1 h temporal resolution, 0.72×0.72horizon-
tal resolution and 29 hybrid sigma-pressure vertical levels.
This investigated time period was constrained by the avail-
ability of meteorological ERA-Interim data. The dispersion
model considers BC as an inert pollutant, with size distribu-
tion described by a single bin with size ranging from 0.001
to 1 µm in dry particle diameter (Dp). Production was inte-
grated over each size bin while dry and wet removal rates
were calculated using mass-weighted mean diameter in each
bin. Depending on particle size, which takes into account the
particle hygroscopic growth, mechanisms of dry deposition
varied from primarily turbulent diffusion driven removal of
fine aerosols to primarily gravitational settling of coarse par-
ticles (Kouznetsov and Sofiev, 2012). Wet deposition distin-
guished between sub- and in-cloud scavenging by both rain
and snow (Horn et al., 1987; Smith and Clark, 1989; Jylhä,
1991; Sofiev et al., 2006). The sources for BC deposited at
Holtedahlfonna were investigated by tagging the different
emission sectors while computing atmospheric dispersion of
BC. Subsequent to the SILAM runs, a multilinear regres-
sion model based on the median values for atmospheric BC
concentrations and deposition for every single year, between
1980 and 2015, was used to estimate the slope of the mod-
elled temporal BC trends, with coefficients being estimated
with 95 % confidence intervals. An Ftest was applied to test
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12784 M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends?
2005 2010 2015
0
5
10
15
20
0
5
10
15
20
25
EC deposition
-2 -1
(mg m yr )
EC concentration
-1
(µg L )
Year
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
0 5 10 15 20 25
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
Depth (cm)
-1
EC concentration (µg L )
Year
0
50
100
150
200
250
0 5 10 15 20 25
EC concentration
-1
(µg L )
Depth (cm)
(a) (b) (c)
(d)
Apr
2015
Sep
2014
Figure 4. EC concentrations (µgL1) in the Holtedahlfonna stake 10 snow pit and firn core, and EC deposition (mgm2yr1). (a) EC
concentrations of the snow pit against the snow depth. In addition, the April 2015 and approximate September 2014 layers are indicated. (b)
EC concentrations in the firn core (solid line), snow pit (dashed line, same as a) and previous surface snow samples (blue stars) with depth
and year. The previous surface snow measurements are by Forsström et al. (2013). Panels (c) and (d) compare the temporal EC concentrations
(c) and deposition (d) in the firn core. The red dots and error bars in panel (c) indicate average EC concentration and the absolute errors of
samples from which multiple analyses were performed.
Table 1. Annual mean firn core EC concentration and deposition at Holtedahlfonna, stake 10, from 2006 to 2014. The values present total
EC concentrations and deposition averaged over the respective year, assuming that the EC deposition rate has stayed constant throughout the
respective year. Dating uncertainties of the firn core increase the uncertainties of these values.
Year 2006 2007 2008 2009 2010 2011 2012 2013 2014
EC µgL19.9 12.9 15.9 10.4 16.6 8.7 29.6 26.9 28.8
EC mgm2yr19.0 11.9 13.2 7.3 12.8 6.3 25.6 18.4 23.9
if the linear regression relationship between the response and
predictor variables was significant.
Generally, like many models, SILAM agrees better with
observations closer to sources than in the Arctic. In the Arc-
tic the modelled BC concentrations and deposition are sys-
tematically low, but the seasonality in atmospheric BC con-
centrations is captured, specifically capturing the Arctic haze
period (see Fig. 5 and discussion below).
3 Results
3.1 Snow pit EC data
The EC variations in the snow pit covering the end of summer
2014 to April 2015 are shown in Fig. 4a. The EC concentra-
tions ranged between 4.7 and 20.3 µgL1, which is in the
same range as EC concentrations of 1.4, 9.4 and 11.6 µgL1
previously measured at the same site in spring surface snow
of 2007, 2008 and 2009, respectively (Forsström et al., 2009,
2013; Fig. 4b). The snow pit samples show a similar seasonal
trend in EC concentrations as previously observed in Arctic
snow packs with elevated concentrations during spring and
summer and lower values in the autumn and winter (Doherty
et al., 2010, 2013).
3.2 Firn core EC data
The EC concentrations of the shallow firn core are between
3.5 and 24.6 µg L1with an average of 10.4µgL1(Fig. 4b).
The firn core EC concentrations match the snow pit EC ob-
servations for the overlapping part from 80 to 253cm from
the snow surface (Fig. 4b). The annual deposition of EC to
the firn core was calculated using the dating (Sect. 2.3.) of
the core. The EC deposition values in the firn core range from
2.8 to 19 mg m2yr1(on average 10 mg m2yr1). Table 1
presents annual (averaged over calendar years) EC concen-
trations and deposition for 2006 to 2014.
Due to the comparably low temporal resolution of the EC
samples no annual variation can be detected in the firn core,
although the observed EC variation may be partly caused by
some samples covering more of the high BC-laden spring to
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M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends? 12785
1980 1985 1990 1995 2000 2005 2010 2015
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Year
-3
BC concentration (µg m )
(a) Zeppelin, annual BC trend 1980–2015
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0
0.05
0.1
0.15
0.2
0.25
Month
-3
BC concentration (µg m )
(b) Zeppelin, 2006 monthly BC trend
Model
Observations
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Month
-3
BC concentration (µg m )
(c) Zeppelin, 2007 monthly BC trend
Model
Observations Model
Observations
Figure 5. Observed atmospheric BC concentrations compared to modelled atmospheric BC concentrations at Zeppelin monitoring station
Ny-Ålesund, Svalbard. (a) Modelled annual average BC concentrations from 1980 to 2015 and observed annual average BC concentrations
from 2002 to 2011. (b, c) Comparison of modelled and observed monthly average atmospheric BC concentrations for 2006 (b) and 2007 (c).
summer snow (e.g. two vs. zero spring layers) compared to
cleaner winter snow (see Ruppel et al., 2014). The firn core is
too short to indicate any clear temporal trend but, in general,
the EC concentrations and deposition seem to be on a lower
level from 2005 to 2011 and to increase to higher levels from
2012 to 2015 (Fig. 4c and d, Table 1). The temporal trend of
EC deposition is similar to the EC concentration trend ob-
served in the core (Fig. 4c and d).
3.3 Modelled BC data
To evaluate the performance of SILAM for Svalbard and
BC, atmospheric BC observations made at the Zeppelin (Ny-
Ålesund) monitoring site were compared to model results
from the correspondent model grid cell in Fig. 5. Figure 5a
shows the model results from 1980 to 2015 while atmo-
spheric observations were available only for 2002 to 2011.
Both the observations and model results show large varia-
tion in atmospheric BC concentrations from one year to the
next, but with an overall decreasing trend (Fig. 5a). However,
compared to the observations, the model significantly under-
estimates the atmospheric BC concentrations (on average by
a factor of 5). Such underestimations of atmospheric BC con-
centrations are particularly common for the Arctic where pre-
vious comparisons to observations have shown atmospheric
BC concentrations being underestimated in chemistry mod-
els by up to a magnitude (e.g. Koch et al., 2009; Lee et al.,
2013; Dutkiewicz et al., 2014).
Figure 5b and c present the seasonality of observed and
modelled monthly BC concentrations for 2006 and 2007.
The model captures the seasonality seen in the observations
but fails to reproduce the magnitudes observed especially in
spring time. Note that the timing of observed spring peaks
(Arctic haze) varies from year to year. This corroborates
with several multi-model studies (Shindell et al., 2008; Koch
et al., 2009; Eckhardt et al., 2015) showing that atmospheric
models are usually not able to simulate the seasonality of
BC in the Arctic precisely, typically underestimating the Arc-
tic haze season occurring during the winter and early spring.
1980 1985 1990 1995 2000 2005 2010 2015
-2 -1
BC deposition (mg m yr )
-3
Atmospheric BC concentration (µg m )
0
1
2
0
0.01
0.02
Year
BC concentration
BC deposition
Figure 6. Modelled annual BC deposition and atmospheric concen-
trations at Holtedahlfonna.
A more detailed discussion on the uncertainties of the model
and input driving the runs is presented in Sect. 4.
The results of modelled atmospheric BC concentrations
and BC deposition at Holtedahlfonna are presented in
Fig. 6. The modelled annual atmospheric BC concentra-
tions decrease quite constantly from 1990 onwards after no-
tably higher values modelled for the 1980s (slope 1.3×
105µgm3yr1;p < 0.001). The modelled BC deposition,
in contrast, shows significant variation from year to year with
no clear trend over the study period. Statistically, the depo-
sition trend decreases weakly over 1980 to 2015, but this
trend is not significant (slope = −3.9×103µgm3yr1;
p=0.09). The modelled atmospheric BC concentration and
deposition trend correlate only weakly (r=0.29, p=0.08)
over the study period.
The model results suggest that the total BC deposition is
dominated by wet deposition at Holtedahlfonna (98.7 %).
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12786 M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends?
1980 1985 1990 1995 2000 2005 2010 2015
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Year
(b) Atmospheric BC concentration
awb
dom
ene
fire
flr
ind
ships
tra
wst
(a) BC deposition
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1980 1985 1990 1995 2000 2005 2010 2015
Year
Figure 7. The annual source sector contribution to the modelled total BC deposition and atmospheric BC concentrations at Holtedahlfonna
between 1980 and 2015. The sources for (a) BC deposition and (b) atmospheric BC concentrations. The emission sectors are as follows: awb
is agricultural waste burning, dom is domestic, ene is energy production, fire is natural fires, flr is flaring, ind is industry, ships is shipping,
tra is transport and wst is waste incineration.
There are notable differences in the source contributions
for the modelled BC deposition and atmospheric BC concen-
trations at Holtedahlfonna (Fig. 7). Over the period of 1980
to 2015 transport and domestic emissions are the most impor-
tant sources for BC deposited at Holtedahlfonna (Fig. 7a),
both with ca. 30 % contribution, while the domestic sector
(43 % on average) is the most important emission source
for atmospheric BC concentrations at the glacier, followed
by the industry and transport sectors (Fig. 7b). For both the
modelled atmospheric BC concentrations and deposition the
contribution of domestic emissions has decreased during the
investigated time period while the contribution of transport,
including shipping, and natural fires has increased, and the
contribution of industry and other sectors has stayed quite
constant.
4 Discussion
4.1 Comparison of the snow and firn core EC data with
the 2005 ice core
Previous EC concentrations from surface snow in 2007, 2008
and 2009 (Forsström et al., 2013) and the snow pit and firn
core data collected from the Holtedahlfonna 2015 coring site
(stake 10) corroborate each other (Fig. 4b). However, the firn
core EC concentrations measured at stake 10 (an average of
10.4 µg L1) are notably lower than recorded in the 300-year
ice core collected from a different site on the same glacier
in 2005 (on average 35.8µgL1) (Ruppel et al., 2014). At
the same time, the overall annual EC deposition in the firn
core (on average 10mgm2yr1) compares quite well to the
EC deposition recorded in the 300-year ice core (on average
11.2 mg m2yr1). However, there is a notable drop of a fac-
tor of 2.5 in the EC deposition values from the last data point
in the 300-year ice core (of 23.7 mgm2yr1deposited in
the sample covering ca. 2001 to 2003) to the first sample in
the firn core (9.3 mgm2yr1deposited between ca. mid-
2005 and early 2006) (Fig. 8). Regrettably, the new firn and
old ice core do not temporally overlap, and therefore it can-
not be confirmed whether the measurements at the separate
coring locations are directly comparable. In the following we
discuss the hypothesis of an actual rapid drop in EC deposi-
tion having occurred between the end of 2003 and mid-2005
at Holtedahlfonna, as suggested by the current data. Sec-
ondly, we explore the hypothesis that this difference in EC
deposition is caused by local post-depositional factors at the
coring sites, impeding the comparison of the cores. In addi-
tion, the sources for the deposited EC are examined.
4.1.1 Post-depositional processes affecting EC
deposition at the two Holtedahlfonna coring sites
EC concentrations in snow and ice are strongly affected
by numerous additional factors to atmospheric BC concen-
trations, such as EC scavenging efficiencies, precipitation
amounts and post-depositional processes of wind drift, sub-
limation and melt, that may dilute or concentrate EC in the
snow (e.g. Doherty et al., 2010, 2013). Snow accumulation
rates and post-depositional factors may vary locally, poten-
tially causing differences in EC concentrations between the
two Holtedahlfonna coring sites located 2.8 km apart (Fig. 1).
Previous results on EC or BC concentrations in surface snow
and full vertical snow profiles have shown that EC concen-
trations and column loads can vary substantially (commonly
of a factor of 2, but even a factor of 16 has been reported)
even on a metre-to-metre scale due to post-depositional pro-
cesses (e.g. Doherty et al., 2010, 2016; Svensson et al., 2013;
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M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends? 12787
0
10
20
30
40
1860 1880 1900 1920 1940 1960 1980 2000 2020
Year
-2 -1
EC deposition (mg m yr )
0
10
20
30
40
Figure 8. EC deposition at Holtedahlfonna between 1850 and 2015. EC deposition (mgm2yr1) in the 2005 ice core (black curve; Ruppel
et al., 2014) and in the shallow firn core (red curve) collected from different sites (see Fig. 1) on Holtedahlfonna.
Forsström et al., 2013; Delaney et al., 2015). Consequently,
the similarity in EC concentrations measured at stake 10
(2015 coring site) from the surface snow, snow pack and
firn core samples gives confidence on the reproducibility of
the used EC analysis method. At the same time, in light
of the commonly found small-scale horizontal variation in
EC and BC concentrations discussed above, the differences
in EC concentrations observed between the 2005 and 2015
Holtedahlfonna coring sites are not unexpected.
In contrast, EC deposition at a specific site is generally
not affected by post-depositional processes, as long as EC is
not transported laterally after deposition (e.g. Ruppel et al.,
2014). The atmospheric processes are expected to be the
same for the Holtedahlfonna sites, which consequently likely
receive the same amount of EC input from the atmosphere.
However, geomorphological properties of the coring sites,
such as topography, differ between the sites, which may re-
sult in different amounts of snow being deposited at the sites
by lateral transport (redistribution) of snow. The 2005 site is
located 50 m higher in altitude at a point more exposed to
wind activity than the 2015 coring site that is located on the
central line of the glacier where mass-balance measurements
are performed (Fig. 1). Indeed, the 2005 core site records
notably less annual net accumulated material (on average
0.5 m water equivalent per year (mw.e.yr1) between 1960
and 2004) than the 2015 site (on average 0.78mw.e.yr1
between 2003 and 2015). The different snow accumulation
rates may indicate that different post-depositional processes
affect or dominate at the sites, consequently causing the an-
nual EC concentrations and deposition to diverge at the sites.
The snow accumulation rate difference has significant con-
sequences for the annual EC concentrations observed at the
sites (higher concentrations at the 2005 site) if the same
amount of precipitation is assumed for the sites (discussed
below). However, if the precipitation amount at the sites is
indeed the same, EC deposition is not directly affected by
the snow accumulation rates (Ruppel et al., 2014), and addi-
tional factors are needed to explain the different EC deposi-
tion rates at the sites. The only process by which the observed
EC deposition in snow and/or an ice core could conceivably
be notably higher at one of nearby locations receiving same
precipitation and atmospheric EC deposition is additional lat-
eral or vertical transport of already deposited EC by wind
activity. These processes affecting the snow accumulation,
EC concentrations and deposition at the sites are discussed
in more detail in the following.
The annual snow accumulation rate is the sum of snow
accumulating (precipitation, wind drift) and reducing (abla-
tion, run-off) processes. The precipitation amount at the sites
is considered the same, and therefore wind drift, summer
melt and sublimation are the probable causes for the different
net snow accumulation at the sites. Summer melt occurs fre-
quently on Holtedahlfonna (Beaudon et al., 2013). However,
BC has a low post-depositional scavenging efficiency due
to its hydrophobic properties; i.e. it is concentrated in melt-
ing snow and not flushed unless the melting is strong (e.g.
Doherty et al., 2013). No summer surface run-off or high
amounts of refrozen water (signalling strong vertical move-
ment of meltwater) in the snow stratigraphical record have
been observed on Holtedahlfonna, indicating that the sum-
mer melt on Holtedahlfonna is not strong enough to flush EC
laterally or vertically. Therefore, it is unlikely that melting or
run-off would cause the different EC deposition amounts at
the two coring sites.
Consequently, wind drift and sublimation may be the most
plausible post-depositional explanations for the observed dif-
ferences in snow accumulation rate and EC deposition lev-
els at the two coring sites, as these processes actually have
the potential to remove or add snow and EC to the annual
snow pack. Redistribution of snow mass by wind drift has
significant impacts on the snow accumulation rates on Sval-
bard (Jaedicke and Gauer, 2005; Beaudon et al., 2011; Sauter
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12788 M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends?
et al., 2013). Sauter et al. (2013) showed that on Vestfonna
ice cap, eastern Svalbard, up to 20 % of primary accumulated
snow is redistributed by wind drift. To explain the higher
EC deposition at the 2005 site it should receive more EC-
laden snow by wind drift than the 2015 site. Higher wind drift
could also explain higher EC concentrations at the site, since
part of snow mass is sublimated during its transport (Sauter
et al., 2013), which concentrates EC in wind-blown snow.
However, if the higher EC deposition at the 2005 site would
be solely explained by it receiving more snow by wind drift
than the 2015 site, then its snow accumulation rate should
also be higher than that of the 2015 site. As the snow accu-
mulation rate is actually lower at the 2005 than the 2015 site,
wind drift cannot explain the differences alone.
Sublimation, which is a function of air temperature, hu-
midity and wind speed, may affect the varying net snow ac-
cumulation rate at the Holtedahlfonna coring sites, as Arctic
winter sublimation commonly reaches values of 10–50% of
total winter precipitation (Liston and Sturm, 2004, and ref-
erences therein). During sublimation water is lost from the
snow pack while EC is left behind and concentrated (e.g. Do-
herty et al., 2010, 2013). The 2005 site is most likely windier
than the 2015 site and may therefore be more prone to sub-
limation, which would result in the lower net snow accumu-
lation rate observed at this site compared to the 2015 site.
However, although significant amounts of water may be lost
from snow/glacier surfaces due to sublimation, this process
does not affect EC deposition rates.
Thus, to explain simultaneously the differences in snow
accumulation rates and EC deposition amounts at the two
Holtedahlfonna coring sites by post-depositional processes,
a combination of high snow drift and sublimation would need
to be considered. However, the differences in snow accumu-
lation rates and EC values between the sites are so large that
based on current knowledge on the amount of snow remobi-
lization by wind and sublimation discussed above, it seems
improbable that these processes would explain the differ-
ences between the sites alone.
Consequently, while the post-depositional processes cer-
tainly affect the measured snow accumulation rate and EC
concentration, as well as wind drift the EC deposition, none
of these processes are alone or together likely to entirely ac-
count for the different level of EC deposition observed in
the 2005 and 2015 firn/ice cores. It is therefore more plausi-
ble that a drop in EC deposition has occurred between 2003
and 2005 at the Holtedahlfonna glacier. The magnitude of
this drop remains uncertain, since the differences between
the ice and firn core are affected by the above described
post-depositional processes to an unknown extent. Sudden
drops are not unprecedented in the 300-year Holtedahlfonna
record, in which EC deposition has dropped strongly, for in-
stance from peak values of 34 mgm2yr1around 1908 to
14 mg m2yr1in 1913 (Fig. 8). At the same time, it should
be kept in mind that previous long-term records comparing
EC (or BC) variations at different coring locations on the
same glacier analysed with the same methods are largely
missing. Therefore, it is ultimately unverified whether such
notable differences in EC values are common due to local
differences between coring sites or indicate actual EC varia-
tion events on the glacier.
4.1.2 Variation in modelled atmospheric BC deposition
at Holtedahlfonna between 1980 and 2015
Atmospheric BC deposition at Holtedahlfonna (as at remote
Arctic regions in general) is a complex end result of BC emis-
sions within and outside of the Arctic, the prevailing atmo-
spheric transport pathways, meteorological conditions along
the way to Svalbard, BC ageing processes and local meteo-
rological processes at the glacier. All these factors contribute
to what emission source areas and sectors are the most sig-
nificant for the EC deposited at Holtedahlfonna, how much
of the emitted BC is scavenged and deposited from the at-
mosphere before reaching Holtedahlfonna, how efficient in-
cloud and below-cloud BC scavenging is at a specific time
at Holtedahlfonna, and thereby how much atmospheric and
in-cloud EC present at Holtedahlfonna is actually deposited.
These processes may vary temporally with notable effects
on the observed EC deposition trend at Holtedahlfonna. As
according to our model results almost 99 % of BC is wet-
deposited at Holtedahlfonna, the significance of meteorolog-
ical processes and their variation in comparison to sole BC
emissions for the observed EC deposition trend have to be
considered. Moreover, it would be a gross oversimplifica-
tion to assume that the EC deposition trend at Holtedahl-
fonna would solely reflect BC emission trends in source ar-
eas and/or atmospheric BC concentration trends, since local
and regional meteorological processes affect the EC deposi-
tion rate notably. As a possible example of the consequences
of disregarding temporal meteorological variation, previous
modelling results of historical BC deposition in Finland us-
ing constant (year 1997) meteorology since 1850 show that
the modelled BC deposition trend closely follows the in-
ventory BC emission trend, while the observed BC deposi-
tion trend clearly diverged from the modelled trend (Ruppel
et al., 2015). One possible explanation for the described dis-
crepancy are variations in meteorological processes affect-
ing BC scavenging efficiencies that were unaccounted for in
the model. Thus, to produce generally more plausible mod-
elled data, atmospheric BC deposition at Holtedahlfonna was
here modelled only beginning from 1980, the start of ERA-
Interim meteorological data.
Atmospheric BC concentration trends, in contrast, have
been generally observed to follow BC emission trends in
the Arctic (e.g. Sharma et al., 2013). In our results the mod-
elled atmospheric BC concentration decreases between 1980
and 2015 (Fig. 6), as has also been observed between 1990
and 2009 at the three long-term Arctic BC monitoring sta-
tions in Alert, Barrow and Ny-Ålesund (Sharma et al., 2013),
and in a 47-year weekly measurement record from north-
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M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends? 12789
ern Finland (Dutkiewicz et al., 2014). The modelled atmo-
spheric BC concentrations at Holtedahlfonna underestimate
the values measured at the closest measurement station, Ny-
Ålesund (Zeppelin), from 2001 to 2015 by an order of mag-
nitude (see Sharma et al., 2013). However, the comparison
between these sites should be done carefully, since the sites
are located in different grid cells in the model and at differ-
ent altitudes (Holtedahlfonna at 1150 ma.s.l.in comparison
to Zeppelin at 440 ma.s.l.) and are therefore subjected to dif-
ferent wind and precipitation forcing. In addition, the moni-
toring station measures BC absorption which is converted to
concentrations using a mass absorption coefficient, whereas
the model output is mass concentration. Despite the problems
of comparing absolute measured and modelled atmospheric
BC concentrations at these sites, they both show the same
decreasing trend.
Notably, however, the modelled annual BC deposition
does not clearly follow (or correlate to) the declining north
of 40N BC emissions (Fig. 3b) or modelled and measured
atmospheric BC concentration trends (Fig. 6). Instead, the
modelled BC deposition shows significant variation from
year to year. The modelled BC deposition trend follows the
wet deposition pattern at the site, which varies mostly irre-
spective of peaks or minima in the atmospheric BC concen-
trations. Consequently, the modelled BC deposition seems
for the most part to be driven by other parameters, for ex-
ample by meteorological processes, rather than atmospheric
BC concentrations. However, over the whole study period the
modelled BC deposition trend is decreasing weakly, as dis-
cussed in Sect. 3.3., similar to the modelled atmospheric BC
concentration trend, although the rate of the deposition de-
crease is not as evident as for the concentrations due to strong
yearly variations (Fig. 6).
The modelled BC deposition at Holtedahlfonna is about
a magnitude lower than the measured EC deposition in the
ice and firn cores (Fig. 9). Similar notable underestimations
in modelled BC values compared to observations have been
previously reported in the Arctic for both snow BC con-
centrations (e.g. Forsström et al., 2013) and BC deposition
(e.g. Ruppel et al., 2013, 2015). The modelled BC deposi-
tion trend at Holtedahlfonna does not show clear consistency
with the observed EC deposition in the ice and firn cores, al-
though some similarities can be observed. The notable vari-
ation in the measured ice/firn core EC deposition from one
data point to the next in addition to the year-to-year variation
in the modelled BC deposition highlights the significance of
wet deposition patterns and underlying varying meteorolog-
ical processes to the surface deposition trends. In addition,
the modelled BC deposition trend seems to support a no-
table drop in BC deposition observed between the ice and
firn core. The 300-year ice core recorded an average EC de-
position of 18.5 mgm2yr1between 1980 and 2003 and the
firn core an average EC deposition of 10mgm2yr1be-
tween 2005 and 2015. This corresponds to a drop of 46 % in
the observed EC deposition at Holtedahlfonna between the
1980 1985 1990 1995 2000 2005 2010 2015
0
1
2
3
4
0
10
20
30
40
-2 -1
Modelled BC deposition (mg m yr )
-2 -1
Observed EC deposition (mg m yr )
Year
Obs. EC deposition
5-yr average
Mod. BC deposition
5-yr average
Figure 9. Modelled BC deposition compared to ice and firn core
EC deposition at Holtedahlfonna from 1980 to 2015; 5-year running
averages are included.
respective time periods. In the model results, the average BC
deposition from 1980 to 2003 is 0.8 mgm2yr1and drops
to 0.48 mg m2yr1between 2005 and 2015, which corre-
sponds to a drop of 40 %. Thereby, the model data suggest
that a significant drop in BC deposition may have occurred
at Holtedahlfonna on a decadal scale, although according to
the model results the drop does not seem to have happened as
abruptly as indicated by the ice and firn core data. The model
data do not indicate a clear peak in BC deposition around
the late 1990s as recorded in the 2005 ice core, although
the 5-year running average of the modelled BC deposition
is temporarily lifted from 1994 to 1997. Similarly high BC
deposition values are modelled for the mid-1980s, but with-
out a longer modelled time period it is unclear whether these
modelled high 1980–1990s values would represent similar
increasing and peaking values on a decadal or centennial
scale as recorded in the 2005 ice core between 1970 and the
2000s (Fig. 8). Furthermore, the modelled deposition does
not show an increasing trend from ca. 2005 to 2015 as indi-
cated by the firn core measurements (Fig. 9).
Consequently, the model results support some features of
the ice and firn core observations, such as higher EC deposi-
tion in the 1980s and 1990s and a drop in deposition there-
after, but these variations are smoothed and lowered by the
model in comparison to the ice and firn core values (Fig. 9).
Explanations for the observed variations being smoothed out
in the model results could relate to the spatial and time reso-
lution of meteorology and emissions. The spatial horizontal
resolution of the ERA-Interim meteorology is 0.72×0.72
and 3 h time resolution. This resolution is quite crude for
this study, as it smooths out the spatial and temporal dis-
tribution of meteorological variables and local climate pa-
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12790 M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends?
rameters at the glacier may not be represented accurately
in the model. Also, the validation of ERA-Interim meteo-
rological data shows that the main limitations in the Arctic
are the positive biases in temperature and humidity below
850 hPA, and they do not capture low-level inversions (Dee
et al., 2011). The first may influence whether precipitation is
solid or liquid, changing the precipitation velocities, and the
second may influence the mixing of the lower troposphere. In
addition, the anthropogenic inventory emissions are available
as monthly or annual emissions for only every 5 or 10 years
(Fig. 3), and the data are linearly interpolated between these
data points. Thus, the scenario-based emission data sets may
smooth out modelled BC variations in comparison to the ice
and firn core observations, and consequently the year-to-year
variations in modelled BC deposition are mainly driven by
meteorology. Furthermore, the global bottom-up emission in-
ventories are based on assumptions of emission factors (BC
amount released from certain burned fuel using a given tech-
nology) and estimations of used fuel amounts (e.g. Bond
et al., 2007), but recently the accuracy of the inventories on
the quantity and spatial allocation of BC emissions has been
questioned particularly for the Arctic (Eckhardt et al., 2015;
Huang et al., 2015; Winiger et al., 2017). Possible underesti-
mation of anthropogenic (e.g. Stohl et al., 2013; Huang et al.,
2015) and natural fire (Soares et al., 2015) BC emissions sig-
nificant for the Arctic and their spatial and emission sectoral
misallocation (Winiger et al., 2017) in the emission inven-
tory driving the model may partly cause the underestimations
of atmospheric BC concentrations and consequently lower
BC deposition in the model results compared to the observed
ice and firn core EC deposition and may potentially affect
the modelled BC deposition trend. Furthermore, the current
model set-up does not include a parameterization for aerosol
ageing, while models with ageing processes tend to show
higher BC mass concentrations in the remote Arctic (e.g. Liu
et al., 2011). The dry and wet deposition schemes of SILAM
have been evaluated (Kouznetsov and Sofiev, 2012; Khan
et al., 2017; Sofiev et al., 2011), but currently in SILAM BC
particles grow only based on relative humidity, which may
enhance dry deposition of relatively large BC particles close
to the sources, allowing the dispersion of only very small
particles to the remote Arctic. Consequently, too little BC
(in mass) may be transported and deposited annually in the
Arctic in the model, especially during the Arctic haze sea-
son (Fig. 5). However, without ageing in SILAM, the parti-
cles do not grow via condensation of soluble material during
transportation, resulting in the particles being too small for
dry deposition when reaching the Arctic. The lack of age-
ing processes may lead to an over-domination of Arctic wet
scavenging in the model as particles are too small for dry de-
position, and consequently the result of 99 % wet deposition
at Holtedahlfonna may be exacerbated.
Nonetheless, the modelled BC deposition variation sug-
gests that the BC deposition trend may diverge from the
atmospheric BC concentration trend on an annual scale
(Fig. 6), which is likely explained by meteorological pro-
cesses affecting for instance BC scavenging. Meanwhile,
the model could be improved by including a temperature
dependency to the scavenging efficiency of BC, as Cozic
et al. (2007) showed that the scavenging efficiency of BC in-
creases significantly from temperatures of 20 (10 % BC
scavenged in mixed phase clouds) to 0C (60% scavenged
in liquid clouds).
4.2 Sources contributing to modelled BC deposition
and atmospheric concentrations at Holtedahlfonna
In Ruppel et al. (2014) it was hypothesized that the observed
increase in the Holtedahlfonna ice core EC deposition from
1970 to 2004 could have been partly caused by simultane-
ously increasing flaring emissions from north-western Rus-
sia. That area is a major source for BC in Svalbard (e.g.
Hirdman et al., 2010; Stohl et al., 2013), and according to
Stohl et al. (2013) flaring may contribute to 20–40 % of an-
nual mean surface BC concentrations in Svalbard, but these
emissions have been strongly underestimated or even dis-
regarded in emission inventories (Stohl et al., 2013; Huang
et al., 2015). However, our current model results suggest
a significantly lower contribution of flaring to the BC val-
ues on Holtedahlfonna between 1980 and 2015: ca. 7 % for
the atmospheric concentrations and 2 % for the deposited BC
(Fig. 7). Only in sporadic years, such as 1982 and 2010, is the
flaring contribution suggested to have increased to over 10 %
of the total BC deposited. Interestingly, this modelled con-
tribution of flaring matches well with state of the art dual-
carbon isotope source apportionment measurements of at-
mospheric EC from Tiksi, north-eastern Russia, which sug-
gested flaring to contribute only to 6 % of annual atmospheric
EC concentrations at the site (Winiger et al., 2017). No in-
crease in the contribution of flaring to total BC deposition is
evident in our modelling data from 1980 to 2015 and, even
in the case of possible continued underestimations of flar-
ing in current emission inventories, the hypothesis of Ruppel
et al. (2014) that flaring partly caused the increase observed
in 1970–2004 in the Holtedahlfonna ice core can be rejected
by the current modelling data.
As seen in Fig. 7, there are notable differences in the
source contributions for the modelled BC deposition and
atmospheric concentrations. While transport and domestic
emissions appear to be the most important sources for BC
deposited at Holtedahlfonna, the domestic sector seems to
be the most important emission source for atmospheric BC
concentrations at the glacier. This difference in the source
contribution to the modelled BC deposition vs. atmospheric
concentration can be explained by the difference in emission
location, injection height, transport pathways and removal of
BC from the atmosphere. In the current setting of chemical
transport models, such as SILAM, the physical properties of
the emitted particles (type, size, hygroscopic properties) are
characterized on a low description level, e.g. no aerosol dy-
Atmos. Chem. Phys., 17, 12779–12795, 2017 www.atmos-chem-phys.net/17/12779/2017/
M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends? 12791
namics, and thus no substantial difference in physical prop-
erties between the different emission sectors is present. Nev-
ertheless, in long-term assessments of BC, the meteorology
is key to determining transport pathways and scavenging of
the particles from the atmosphere and may thereby affect the
differences between source contributions of modelled atmo-
spheric and deposited BC.
For the modelled BC deposition, the contribution of do-
mestic emissions has decreased while transport emissions
have generally increased from 1980 to 2015, particularly
when including shipping (Fig. 7a). The BC emissions north
of 40N from the transport sector first increased from 1980
to ca. 2000 and then decreased (Fig. 3). A similar trend is also
identifiable in the modelled source contribution of BC depo-
sition at Holtedahlfonna, although in the 2010s the contribu-
tion of transport increases again (Fig. 7a). While this tempo-
ral evolution of emissions and modelled BC deposition from
the transport sector resemble to some extent the observed EC
deposition trend in the Holtedahlfonna ice and firn cores, the
fraction of transport emissions to the total BC deposited at
Holtedahlfonna seems, based on the model data, too low to
solely explain the recorded ice and firn core EC deposition
trends. Furthermore, the model results show that between
1980 and 2015 the contribution of natural fire emissions to
both the atmospheric BC concentrations and BC deposition
has increased (Fig. 7), as also suggested by their increasing
emissions (Fig. 3). Interestingly, however, natural fires con-
stitute 24 % of total BC emissions north of 40N between
2010 and 2015 in the used emission data, but their contri-
bution to the modelled atmospheric BC concentrations and
BC deposition at Holtedahlfonna is significantly lower, ca.
5 % for both atmospheric composition and deposition in this
time period. This may suggest that natural fire BC emissions
are prone to be washed out of the atmosphere before reach-
ing Svalbard. BC emissions from natural fires appear mostly
in spring and summer and are the dominant source contrib-
utor in this season at Holtedahlfonna, but their contribution
to annual deposition rarely increases to notable values at the
glacier.
In summary, emissions from the domestic and transport
sector, followed by industry, seem to affect the BC values at
Holtedahlfonna the most. None of the anthropogenic or nat-
ural fire emissions have varied independently or together in
a manner that could solely explain the observed EC varia-
tion in the Holtedahlfonna ice and firn cores. Furthermore,
the amount of BC emissions from individual sectors (Fig. 3)
does not equal the modelled contribution of these emission
sectors to the atmospheric BC concentrations or especially
BC deposition at Holtedahlfonna (Fig. 7). Consequently, it
seems most likely that meteorological processes affecting
wet deposition patterns at the glacier (and during transport)
have had a stronger influence on the EC deposition trends at
Holtedahlfonna than the BC emission trends.
5 Conclusions
According to a shallow firn core collected in spring 2015
from Holtedahlfonna glacier, Svalbard, EC concentrations
and deposition have dropped to lower values in the 21st cen-
tury after rapidly increasing values recorded from 1970 to
2004 at the glacier in a 300-year ice core (Ruppel et al.,
2014). Neither the increasing trend from 1970 nor the rapid
drop in EC deposition from 2003 to 2005 is supported by the
Arctic atmospheric BC concentration measurement or BC
emission inventory trends. A meso-to-global-scale chemical
transport model (SILAM) was run to investigate the differ-
ence in atmospheric BC concentration and BC deposition
trends, and to evaluate BC emission sources affecting the
Holtedahlfonna glacier between 1980 and 2015.
Modelling the long-term atmospheric concentrations and
deposition of BC at Holtedahlfonna allowed us to discern the
annual variation and decadal trends for BC. As expected, the
modelled atmospheric BC concentration trend corresponds
to the declining BC emission trend. However, although the
modelled BC deposition decreases weakly throughout the
study period (1980–2015), the trend does not clearly follow
BC emission or atmospheric concentration trends. Our re-
sults show that almost 99 % of BC mass is wet-deposited at
Holtedahlfonna. This number is probably exacerbated by the
lack of aerosol ageing processes in the model which results,
for instance, in the transported particles being too small for
dry deposition in the Arctic and consequently wet scavenging
overly dominating the deposition. Nonetheless, the results
based on the current settings of SILAM corroborate with the
85 to 90 % of BC wet deposition generally suggested for the
Arctic by Wang et al. (2011). Thus, precipitation and other
meteorological factors (such as temperature and cloud phase
(liquid, mixed or ice)) are crucial parameters as they drive
the scavenging of BC, both on site and during the transport
of BC to the Arctic. Consequently, it seems oversimplified to
assume that the BC deposition trend would strictly follow its
emission and/or atmospheric concentration trends.
The modelled BC deposition trend shows similarities with
the observed ice and firn core EC trends, with highest de-
position values reached in the 1980s and 1990s and a sub-
sequent decrease. The ice and firn core data show stronger
variation and steeper fluctuations in EC deposition trends
than the model. This is likely caused by key input data of
the model, as the emission inventory data are based on emis-
sion scenarios that are only available for every 5 or 10 years,
and the model is run with the same grid size as the meteo-
rology (0.72×0.72horizontal resolution), which smooth
out both temporal and spatial variations. Interestingly, the
model results indicate differences in the source contribution
of atmospheric and deposited BC, with domestic BC emis-
sions clearly contributing most to the atmospheric BC con-
centrations and traffic and domestic emissions contributing
equally to the deposited BC. This difference further under-
lines that meteorology, BC transport and chemical ageing in-
www.atmos-chem-phys.net/17/12779/2017/ Atmos. Chem. Phys., 17, 12779–12795, 2017
12792 M. M. Ruppel et al.: Do contemporary emissions determine EC deposition trends?
fluence atmospheric BC concentrations and BC deposition
at Holtedahlfonna differently. Also, the source area location
and whether the emissions are available throughout the year
or are seasonal, affect how they contribute to the atmospheric
concentrations and deposition at the glacier.
Notably, the recorded firn EC concentrations (from 2005
to 2015) are lower than the EC concentrations recorded in
the first half of the 1980s in the 300-year ice core. Simi-
larly decreasing BC concentrations were reported by Doherty
et al. (2010) comparing ca. 1200 surface snow samples col-
lected mainly between 2005 and 2009 to snow collected by
Clarke and Noone (1985) in 1983 and 1984 from Arctic snow
packs, including Svalbard. While Doherty et al. (2010) con-
cluded that it was doubtful that BC in Arctic snow would
have contributed to the rapid decline of Arctic sea ice ob-
served since 1979 (e.g. AMAP, 2011), our ice and firn core
results highlight that such snow measurements provide only
temporal snap shots in a decadal perspective, and significant
BC variation relevant for climate impact assessment may
be overlooked without continuous records. In other words,
only continuous long-term records can reliably show decadal
trends upon which the significance of year-to-year variability
can be assessed.
Observational data on Arctic EC or BC deposition are
currently quite scarce and geographically restricted (mostly
to Greenland and the European Arctic). Moreover, several
firn/ice cores should be retrieved from same glaciers to as-
sess the effect of local post-depositional processes and mi-
crometeorology on the BC concentrations and deposition.
The present data indicate that EC deposition at a Svalbard
glacier is not solely driven by BC emission or atmospheric
concentration trends, as basically all EC is wet-deposited and
thereby mostly affected by precipitation and EC scavenging
efficiency variations. However, it is currently unknown how
widespread or pronounced such discrepancies between atmo-
spheric BC and deposition trends generally are in the Arctic.
Much further BC deposition data are required before general
conclusions on the climatic implications on BC in the Arctic
should be attempted, since it is specifically BC deposition on
reflecting surfaces that amplifies the climate impact of BC
in the Arctic compared to atmospheric BC. Furthermore, the
current data suggest that Arctic BC deposition trends cannot
straightforwardly be reconstructed based on atmospheric BC
concentration trends, or vice versa.
Data availability. The data are available from the authors
(meri.ruppel@helsinki.fi) upon request.
Competing interests. The authors declare that they have no conflict
of interest.
Special issue statement. This article is part of the special issue “In-
teractions between climate change and the Cryosphere: SVALI, DE-
FROST, CRAICC (2012–2016) (TC/ACP/BG inter-journal SI)”. It
is not associated with a conference.
Acknowledgements. We are deeply grateful for the support and
funding received from the NordForsk Top-level Research Initiative
Nordic Centre of Excellence, CRAICC (Cryosphere–Atmosphere
Interactions in a Changing Arctic Climate), and the Academy
of Finland projects 257903 and 296646. The field support was
provided by Norwegian Polar Institute. Support for atmospheric
aerosol observations at Zeppelin (Ny-Ålesund) by the Swedish
EPA is greatly acknowledged.
Edited by: Michael Boy
Reviewed by: two anonymous referees
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... The modeled BC deposition is 1−2 magnitudes lower than the observed SBC fluxes in the sediment records. However, as the sedimentary SBC fluxes do not represent absolute atmospheric BC deposition and may include some BC influx from the catchment area, and models are known to underestimate BC concentrations 44,45 and particularly deposition 8,46 in the Arctic, comparison of relative trends is better justifiable than comparing exact values between model and observations. The temporal trends of the observed SBC fluxes and modeled BC deposition correlate moderately for the years from which 3.3. ...
... However, SBC and elemental carbon deposition trends have increased after 1991 also in northern Finland lake sediments and a Svalbard ice core strongly influenced by much of the same Eurasian emissions as are the current study area ( Figure S7). 7,8 Together, these results imply either an offset between BC emission and observed SBC flux trends, for instance, due to meteorological process affecting BC scavenging efficiency variations 46 or potential underestimations in BC emissions, emission factors, or the temporal trend in Russian emissions, particularly from the oil and gas producing area, since 1991 in emission inventories. The moderately increasing Russian, and particularly oil and gas producing region, CMIP6 emission trend ( Figure S5c) seems clearly underestimated compared to the observed SBC flux trends between 2000 and 2015 ( Figure 2). ...
... Study sites and BC emissions in their vicinity. (A) Locations of the study lakes (yellow dots), previously published lake sediment BC records from northern Finland (green dots),8 and Svalbard,7,9,46 Greenland,56,60 and a Canadian 61 ice core records (green stars). The red line indicates the Arctic as defined by the Arctic Monitoring and Assessment Programme (AMAP). ...
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... Localized studies have also been carried out near Longyearbyen (Aamaas et al., 2011;Khan et al., 2017) and Ny-Ålesund (Sihna et al., 2018;Jacobi et al., 2019). In addition, two ice cores recovered from the Lomonosovfonna and Holtedahlfonna ice fields (Spitsbergen) have provided insights into longer-term variations in BC deposition on Svalbard (Ruppel et al., 2014(Ruppel et al., , 2017Osmont et al., 2018). ...
... (Forsström et al., 2013). For their part, Ruppel et al. (2017) estimated an annual mean L EC snow of 10 mg m −2 using snow samples and a firn core from Holtedahlfonna (HDF) spanning ∼ 8 years (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014). The corresponding mean L EC snow in the late winter (end April) snowpack could be less than half of this value (∼ 5 mg m −2 ), but the high interannual variability in net snow accumulation at this site (Pramanik et al., 2019;Van Pelt and Kohler, 2015) and the uncertainty in the chronology of the firn core make such an estimate tentative at best. ...
... The plot "Glaciers 2007-2017" combines all glacier snowpack data from the present study as well as from earlier glacier surveys by Forsström et al. (2009Forsström et al. ( , 2013. The plot "HDF firn core" is based on the analysis of a firn core from Holtedahlfonna (Ruppel et al., 2017), and the plot "Ny-Ålesund area" is based on the surface snow data presented in Svensson et al. (2013Svensson et al. ( , 2018, and unpublished data (Table S5) (Table S5). Data from Greenland and the Yukon span 3-6 years of accumulation in snow, while the Holtedahlfonna firn core spans an estimated ∼ 8 years (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014). ...
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... BC has an atmospheric lifetime of about 7 d and has been directly targeted in important international mitigation agreements (AMAP, 2015). Theoretical and experimental results showed that the cryosphere is affected both by the BC-induced warming of the atmosphere and by direct and indirect BC effects on the snow once deposited over it (Flanner, 2013), Atmospheric BC measurements in the Arctic regions are still rare, despite an extraordinary effort done by the international scientific community to evaluate the sources, transport paths, concentration and climate impact (Eleftheriadis et al., 2009;Pedersen et al., 2015;Ferrero et al., 2016;Ruppel et al., 2017;Osmont et al., 2018;Zanatta et al., 2018;Laj et al., 2020). BC mass concentrations can be directly measured, by using incandescent or thermal techniques, and indirectly measured, by absorption measurements using an appropriate mass absorption cross section (Petzold, 2013). ...
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... Wet deposition seems to be the preferential pathway as the rBC peak is spread over the whole accumulated snow layer, while dry deposition would rather create a thin and highly concentrated layer. Several studies indicate that rBC is mainly scavenged from the atmosphere via wet deposition processes (Cape et al., 2012;Ruppel et al., 2017;Sinha et al., 2018). The uppermost two layers (A-B, samples 1 to 3) show very low rBC concentrations (average: 0.21 ng g −1 ), in agreement with the clean atmospheric conditions that prevailed on 28 and 29 June with eBC concentrations below 10 ng m −3 . ...
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Black Carbon (BC) is a significant forcing agent in the Arctic, but substantial uncertainty remains to quantify its climate effects due to the complexity of the different mechanisms involved, in particular related to processes in the snow-pack after deposition. In this study, we provide detailed and unique information on the evolution and variability of BC content in the upper surface snow layer during the spring period in Svalbard (Ny-Ålesund). Two different snow-sampling strategies were adopted during spring 2014 and 2015, providing the refractory BC (rBC) mass concentration variability on a seasonal/daily and daily/hourly time scales. The present work aims to identify which atmospheric variables could interact and modify the mass concentration of BC in the upper snowpack, the snow layer which BC particles affects the snow albedo. Despite the low BC mass concentrations, a relatively high daily variability was observed. Atmospheric, meteorological, and snow-related physico-chemical parameters were considered in a multiple statistical model to separate the factors determining observations. Precipitation events were the main drivers of the BC variability. Snow metamorphism and activation of local sources during the snow melting periods appeared to play a non-negligible role (wind resuspension in specific Arctic areas where coal mines were present). The BC content in the snow resulted in being statistically decoupled from the atmospheric BC load.
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Black Carbon (BC) is a major forcing agent in the Arctic but substantial uncertainty remains to quantify its climate effects due to the complexity of mechanisms involved. In this study, we provide unique information on processes driving the variability of BC mass concentration in surface snow in the Arctic. Two different snow-sampling strategies were adopted during spring 2014 and 2015, focusing on the refractory BC (rBC) mass Ny-Ålesund concentration daily/hourly variability on a seasonal/daily time scale (referred to as 80-days and 3-days experiments). Despite the low rBC mass concentrations (never exceeding 22 ng g−1), a daily variability of up to 4.5 ng g−1 was observed. Atmospheric, meteorological and snow-related physico-chemical parameters were considered in multiple statistical models to understand the factors behind the observed variation of rBC mass concentrations. Results indicate that the main drivers of the variation of rBC are the precipitations events, snow metamorphism (melting-refreezing cycles, surface hoar formation and sublimation) and the activation of local sources (wind resuspension) during the snow melting periods. The rBC in the snow seems de-coupled with the atmospheric BC load. Our results highlighted a common association of snow rBC with coarse mode particles number concentration and with snow precipitation events.
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Significance A successful mitigation strategy for climate warming agents such as black carbon (BC) requires reliable source information from bottom-up emission inventory data, which can only be verified by observation. We measured BC in one of the fastest-warming and, at the same time, substantially understudied regions on our planet, the northeastern Siberian Arctic. Our observations, compared with an atmospheric transport model, imply that quantification and spatial allocation of emissions at high latitudes, specifically in the Russian Arctic, need improvement by reallocating emissions and significantly shifting source contributions for the transport, domestic, power plant, and gas flaring sectors. This strong shift in reported emissions has potentially considerable implications for climate modeling and BC mitigation efforts.
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