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Journal ArticleDOI

Globally Significant CO2 Emissions From Katla, a Subglacial Volcano in Iceland

16 Oct 2018-Geophysical Research Letters (John Wiley & Sons, Ltd)-Vol. 45, Iss: 19

AbstractVolcanoes are a key natural source of CO2, but global estimates of volcanic CO2 flux are predominantly based on measurements from a fraction of world's actively degassing volcanoes We combine high‐precision airborne measurements from 2016 and 2017 with atmospheric dispersion modeling to quantify CO2 emissions from Katla, a major subglacial volcanic caldera in Iceland that last erupted 100 years ago but has been undergoing significant unrest in recent decades Katla's sustained CO2 flux, 12–24 kt/d, is up to an order of magnitude greater than previous estimates of total CO2 release from Iceland's natural sources Katla is one of the largest volcanic sources of CO2 on the planet, contributing up to 4% of global emissions from nonerupting volcanoes Further measurements on subglacial volcanoes worldwide are urgently required to establish if Katla is exceptional, or if there is a significant previously unrecognized contribution to global CO2 emissions from natural sources We combine high‐precision airborne measurements from 2016 and 2017 with atmospheric dispersion modelling to quantify CO2 emissions from Katla, a major subglacial volcanic caldera in Iceland that last erupted 100 years ago but has been undergoing significant unrest in recent decades Katla's sustained CO2 flux, 12‐24 kt/d, is up to an order of magnitude greater than previous estimates of total CO2 release from Iceland's natural sources Katla is one of the largest volcanic sources of CO2 on the planet, contributing up to 4% of global emissions from non‐erupting volcanoes Further measurements on subglacial volcanoes world‐wide are urgently required to establish if Katla is exceptional, or if there is a significant previously unrecognized contribution to global CO2 emissions from natural sources

Topics: Volcano (51%)

Summary (2 min read)

1. Introduction

  • Volcanoes are one of the most important natural sources of carbon dioxide (CO2), but empirical measurements are available for only ~20% of major volcanic gas emission sources (reviewed in Burton et al., 2013).
  • The authors study is the first to report the CO2 flux from a subglacial volcano in Iceland by measuring the gas directly in the atmosphere.
  • Measurements of gas emissions from subglacial volcanic systems are important for understanding the underlying magma systems and, subsequently, for forecasting their eruptions, which are typically highly hazardous due to the generation of ash and jökulhlaups (flash floods of glacial melt water).

1.1. Katla Volcanic System

  • The subglacial Katla volcanic system is one of the largest andmost active ones in Iceland and has erupted 1–3 times per century since the settlement of Iceland 1,100 years ago (Larsen, 2000), and up to 6 times per century in prehistoric times (Óladóttir et al., 2008).
  • The eruptions within the glaciated part are typically accompanied by tephra generation (bulk volume 0.02–2 km3) and jökulhlaups due to the magma-ice interaction (Larsen, 2000).
  • There are two main areas of geophysical unrest—within the caldera, and near the Goðabunga rise on the western part of the central volcano (e.g., Jónsdóttir et al., 2009).
  • The smell of hydrogen sulfide (H2S) is commonly reported near the outlet rivers, in particular duringmajor andminor jökulhlaups (Bergsson, 2016).
  • A DOAS UV spectrometer installed on the flanks of Katla since July 2017 has never detected sulfur dioxide (SO2) (Icelandic Met Office monitoring data).

2.1. Airborne Observations

  • The airborne observations were made using the atmospheric research aircraft (a highly modified BAE-146 aircraft) of the Facility for Airborne Atmospheric Measurements (http://www.faam.ac.uk).
  • Details about the instrumentation are in Text S1 in the supporting information.
  • Flight paths were selected based on the prevalent wind direction in order to obtain downwind measurements of active volcanoes.
  • No flights traversing the subglacial caldera were possible in 2016 or 2017 due to cloud cover over the glacier.
  • The full tracks of the flights reported in this paper are shown in Figure S1 in the supporting information.

2.2. Gas Source Modeling

  • In order to identify the source of the excess CO2, the authors applied two approaches.
  • The second involved simulating the effects of a variety of plausible sources within a very high resolution numerical weather prediction model (Weather Research and Forecasting model [WRF]; full details about the model Text S1) and comparing the distribution of dispersed gases within the model with the observations.
  • Results of HYSPLIT are included in supporting information .
  • For the sources in theWRF simulations the authors initially used the 32 volcanic systems in Iceland and ran theWRFmodel with CO2 as a passive tracer.
  • This confirmed unequivocally that the source was in the region of Katla, leading us to make further measurement flights in 2017, and more detailed simulations of the Katla region in order to identify the source of the gas.

2.3. Gas Emission Rate Calculations

  • As the exact location and number of the degassing sources within the large glacier (590 km2) overlying Katla were unknown, the calculation of the CO2 emission rate (“flux”) presented a challenge not previously reported in studies using airborne measurements.
  • The authors calculated the CO2 flux using two independent methods, direct calculations and model simulations.
  • The interpolation techniques were inverse distance weighting (IDW in Table 1) for all of the flights and fitting of a Gaussian plume dispersion model (Gaussian in Table 1).
  • Coupled with dense gas dynamics, WRF is essential here for effective source identification.

3.2. CO2 Emission Rate From Katla

  • In Iceland, the previous estimates of total natural CO2 flux amounted to 2.7–5.8 kt/d (Ármannsson et al., 2005) and included emissions from only four volcanic systems (Grímsvötn, Eyjafjallajökull, Hekla, and Krafla).
  • These measurements are ill-suited to determining the total flux of CO2 being released, nor are they suitable for determining the maximum concentrations of CO2 released, as this would need to be measured at the mouth of the outlet river, an unstable, dynamic environment where permanent installations are unsustainable.
  • The authors share these results here to show that there are additional, noncontinuous, ground-level emissions of CO2 from Katla volcano that may not be captured in their aircraft-based assessment.
  • Ground-based CO2 concentration measurements during a jökulhlaup were made at the outlet river Jökulsá á Sólheimasandi in July 2014, with values of up to 12,000-ppm CO2.

4. Conclusions

  • The discovery of a very large CO2 emission from Katla volcano is novel, as Katla was thought to be a minor emitter of gases between the periodic jökulhlaups and eruptions (last eruption in 1918 C.E.).
  • The authors have shown unequivocally that Katla volcanic system as a whole is a source of CO2, but the exact location(s) of the degassing sources is still unknown (and are potentially dynamic).
  • Further direct observations are needed to locate these sources with greater accuracy.
  • The collection of a CO2 flux time series andmeasurements of other gas species, including, for example, hydrogen sulfide andmethane, will therefore be critical for furthering their understanding.
  • Only 3 of the measured 33 volcanoes were subglacial (Redoubt, Spurr, and Grímsvötn).

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The University of Manchester Research
Globally Significant CO2 Emissions From Katla, a
Subglacial Volcano in Iceland
DOI:
10.1029/2018GL079096
Document Version
Final published version
Link to publication record in Manchester Research Explorer
Citation for published version (APA):
Ilyinskaya, E., Mobbs, S., Burton, R., Burton, M., Pardini, F., Pfeffer, M. A., Purvis, R., Lee, J., Bauguitte, S.,
Brooks, B., Colfescu, I., Petersen, G. N., Wellpott, A., & Bergsson, B. (2018). Globally Significant CO2 Emissions
From Katla, a Subglacial Volcano in Iceland. Geophysical Research Letters, 45(19), 10,332-10,341.
https://doi.org/10.1029/2018GL079096
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Geophysical Research Letters
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Download date:10. Aug. 2022

Globally Signicant CO
2
Emissions From Katla, a Subglacial
Volcano in Iceland
Evgenia Ilyinskaya
1
, Stephen Mobbs
2
, Ralph Burton
2
, Mike Burton
3
, Federica Pardini
3
,
Melissa Anne Pfeffer
4
, Ruth Purvis
5
, James Lee
5
, Stéphane Bauguitte
6
, Barbara Brooks
2
,
Ioana Colfescu
2
, Gudrun Nina Petersen
4
, Axel Wellpott
6
, and Baldur Bergsson
4
1
School of Earth and Environment, University of Leeds, Leeds, UK,
2
National Centre for Atmospheric Science, Fairbairn
House, University of Leeds, Leeds, UK,
3
School of Earth and Environmental Sciences, Williamson Building, University of
Manchester, Manchester, UK,
4
Icelandic Meteorological Ofce, Reykjavik, Iceland,
5
National Centre for Atmospheric Science,
Innovation Way, University of York, York, UK,
6
Facility for Airborne Atmospheric Measurements, Craneld University,
Craneld, UK
Abstract Volcanoes are a key natural source of CO
2
, but global estimates of volcanic CO
2
ux are
predominantly based on measurements from a fraction of worlds actively degassing volcanoes. We
combine high-precision airborne measurements from 2016 and 2017 with atmospheric dispersion modeling
to quantify CO
2
emissions from Katla, a major subglacial volcanic caldera in Iceland that last erupted
100 years ago but has been undergoing signicant unrest in recent decades. Katlas sustained CO
2
ux,
1224 kt/d, is up to an order of magnitude greater than previous estimates of total CO
2
release from Icelands
natural sources. Katla is one of the largest volcanic sources of CO
2
on the planet, contributing up to 4% of
global emissions from nonerupting volcanoes. Further measurements on subglacial volcanoes worldwide are
urgently required to establish if Katla is exceptional, or if there is a signicant previously unrecognized
contribution to global CO
2
emissions from natural sources.
Plain Language Summary We discovered that Katla volcano in Iceland is a globally important
source of atmospheric carbon dioxide (CO
2
) in spite of being previously assumed to be a minor gas
emitter. Volcanoes are a key natural source of atmospheric CO
2
, but estimates of the total global amount of
CO
2
that volcanoes emit are based on only a small number of active volcanoes. Very few volcanoes that
are covered by glacial ice have been measured for gas emissions, probably because they tend to be difcult
to access and often do not have obvious degassing vents. Through high-precision airborne measurements
and atmospheric dispersion modeling, we show that Katla, a highly hazardous subglacial volcano that last
erupted 100 years ago, is one of the largest volcanic sources of CO
2
on Earth, releasing up to 4% of total
global volcanic emissions. This is signicant in a context of a growing awareness that natural CO
2
sources
have to be more accurately quantied in climate assessments, and we recommend urgent investigations of
other subglacial volcanoes worldwide.
1. Introduction
Volcanoes are one of the most important natural sources of carbon dioxide (CO
2
), but empirical measure-
ments are available for only ~20% of major volcanic gas emission sources (reviewed in Burton et al.,
2013). Extrapolations of these measurements give an estimated a global subaerial geological emission rate
of ~1,500-kt/d CO
2
(Burton et al., 2013), which is ~2% of the anthropogenic emission rate of ~96,000 kt/d
(Friedlingstein et al., 2010). Updated measurements of degassing from arc volcanoes, for example, Aiuppa
et al. (2017), demonstrate that there are still large uncertainties. The quanti cation of CO
2
emissions from
previously unmeasured volcanic sources is therefore critical. While subglacial volcanoes are numerous, they
are grossly underrepresented in terms of volcanic gas measurements (3 out of the 33 volcanoes reviewed in
Burton et al., 2013), potentially because they often lack a visible gas plume and/or are more difcult to
access. In Iceland, gas measurements of CO
2
uxes from the 32 active volcanic systems are sparse, and only
2 out of its 16 subglacial volcanoes (Grímsvötn and Eyjafjallajökull) have been measured (Table 1). The
reported uxes CO
2
from nonerupting volcanoes are relatively low, with a maximum of 0.5 kt/d from
Grímsvötn (Ágústsdóttir & Brantley, 1994). Due to the low number of available measurements, the estimates
of total volcanic CO
2
ux in Iceland, 2.75.8 kt/d (Arnórsson & Gislason, 1994; Hernández et al., 2012;
ILYINSKAYA ET AL. 10,332
Geophysical Research Letters
RESEARCH LETTER
10.1029/2018GL079096
Key Points:
Subglacial volcanoes are
underrepresented in terms of gas
monitoring, but we show that they
can be major emitters of CO
2
Katla volcano is found to be one of
largest volcanic sources of CO
2
on
the planet, contributing up to 4% of
all nonerupting volcanoes
High-precision airborne
measurements combined with
atmospheric modeling are a
powerful method to monitor poorly
accessible volcanoes
Supporting Information:
Supporting Information S1
Correspondence to:
E. Ilyinskaya,
e.ilyinskaya@leeds.ac.uk
Citation:
Ilyinskaya, E., Mobbs, S., Burton, R.,
Burton, M., Pardini, F., Pfeffer, M. A., et al.
(2018). Globally signicant CO
2
emissions from Katla, a subglacial
volcano in Iceland. Geophysical Research
Letters, 45, 10,33210,341. https://doi.
org/10.1029/2018GL079096
Received 5 JUN 2018
Accepted 10 SEP 2018
Accepted article online 17 SEP 2018
Published online 7 OCT 2018
©2018. American Geophysical Union.
All Rights Reserved.

Pálmason et al., 1985), are poorly constrained and are likely too low (Ármannsson et al., 2005). The CO
2
ux
from Grímsvötn and Eyjafjallajökull were estimated by analyzing gas content dissolved in melt water accu-
mulating under the ice that likely underestimates the ux as CO
2
degasses very rapidly when the water is
depressurized. Our study is the rst to report the CO
2
ux from a subglacial volcano in Iceland by measuring
the gas directly in the atmosphere.
Measurements of gas emissions from subglacial volcanic systems are important for understanding the under-
lying magma systems and, subsequently, for forecasting their eruptions, which are typically highly hazardous
due to the generation of ash and jökulhlaups (ash oods of glacial melt water). Recent studies across differ-
ent tectonic and geographical settings have demonstrated that increases in CO
2
output can precede erup-
tions by months to years, for example, at Redoubt in the Aleutians (Werner et al., 2012), Kilauea in Hawaii
(Poland et al., 2012), and Villarica in Chile (Aiuppa et al., 2017) but it is not yet known if this applies to any
of the Icelandic volcanoes.
1.1. Katla Volcanic System
The subglacial Katla volcanic system is one of the largest and most active ones in Iceland and has erupted 13
times per century since the settlement of Iceland 1,100 years ago (Larsen, 2000), and up to 6 times per
century in prehistoric times (Óladóttir et al., 2008). The current repose period is the longest one on record,
with the last conrmed eruption in 1918 C.E. Katla system consists of a central volcano (max altitude
1,500 m above sea level [asl]) and 80-km long ssure system. The central volcano is partially covered by
the vast 590-km
2
Mýrdalsjökull glacier, which is on average ~200 m thick, reaching 700-m thickness in
Table 1
CO
2
Flux (kt/d With Standard Error) From Katla Volcano Compared With Other Volcanoes in Iceland (kt/d, Minimum and Maximum Values) for Which Data Have
Been Published
Methods
Katla only
Volcano
Date (ight
number for Katla)
CO
2
ux
(kt/d) Approach
Number
of ight
tracks
CO
2
max
(ppm)
Altitude of
CO
2
plume
(m above
sea level)
Flux
calculation
method
Katla, western ank 18 Oct 2016 (B987) 19.6 ± 3.2 Airborne direct
observations
12 432 100600 IDW
15 Simulation SMF
20 Oct 2016 (B989) 14.6 ± 3.2 Airborne direct
observations
13 413 8401,200 IDW
11.9 ± 5.4 Gaussian
510 Simulation SMF
04 Oct 2017 (C060) 12.8 ± 1.3 Airborne direct
observations
3 432 890970 IDW
510 Simulation SMF
Katla, central caldera 04 Oct 2017 (C060) 11.4 ± 2.7 Airborne direct
observations
7 415 380650 IDW
510 Simulation SMF
Grímsvötn (Ágústsdóttir &
Brantley, 1994)
19541991 0.53 Subglacial melt water
from the caldera
Eyjafjallajökull (Gíslason, 2000) 2000 0.0070.070 Subglacial melt water
from the caldera
Hekla (Gislason et al., 1992) 19881991 0.19 Gas dissolved in
groundwater
Hekla (Ilyinskaya et al., 2015) 20122013 0.044 Diffuse soil emissions
Reykjanes (Fridriksson et al., 2006,
Fridriksson et al., 2010)
20042009 0.0120.019 Diffuse soil emissions
Hengill (Hernández et al., 2012) 2006 0.45 Diffuse soil emissions
Kraa (Ármannsson et al., 2007) 20042006 0.23 Diffuse soil emissions
Note. For Katla airborne measurements, the table shows the number of ight tracks that passed through the plume, the max CO
2
concentration measured on each
ight, and the altitude at which the CO
2
plume was found. Methods used for Katla CO
2
ux calculations: IDW, inverse distance weighting; Gaussian, tting of a
Gaussian plume dispersion model; SMF, specied mass ux.
10.1029/2018GL079096
Geophysical Research Letters
ILYINSKAYA ET AL. 10,333

places. The central volcano contains a large, ice-lled caldera (110 km
2
, Figure 1). The eruptions within the
glaciated part are typically accompanied by tephra generation (bulk volume 0.022km
3
) and jökulhlaups
due to the magma-ice interaction (Larsen, 2000). The ssure swarm has produced large effusive basaltic
eruptions with lava volumes 18 km
3
(Thordarson et al., 2003). The size and proximity to populations of
Katla mean that the next eruption will likely have major local and possibly regional impacts, whether it
occurs within the glaciated or nonglaciated part of the system. Disturbance to international aviation by
ash is likely, even if the eruption is small in size (Biass et al., 2014).
Katla has had recurring geophysical unrest (seismicity and ground deformation), but the presence of glacial ice
makes the subsurface signals difcult to interpret. Previous studies have disagreed on whether unrest in differ-
ent parts of the system is caused by movements of magma (e.g., Soosalu et al., 2006; Sturkell et al., 2008), or
movements of glacial ice and its seasonal changes (e.g., Jónsdóttir et al., 2009; Spaans et al., 2015). Katla has
an annual average of ~300 earthquakes (Icelandic Met Ofce monitoring data) and periodic escalations of
up to a few thousand earthquakes. The majority of the earthquakes are at 0- to 5-km depth and <2.5 in mag-
nitude, with rarer occurrences of deeper (up to 20-km depth) and larger events (magnitude 4). There are two
main areas of geophysical unrestwithin the caldera, and near the Goðabunga rise on the western part of the
central volcano (e.g., Jónsdóttir et al., 2009). The largest unrest periods since the last conrmed eruption have
occurred in 1955, 1999, and 2011 C.E. These periods had increased seismicity for months to years, increased
geothermal activity, and signicant jökulhlaups that caused damage to infrastructure (Sturkell et al., 2008). It
has not been conclusively shown whether these episodes were associated with small subglacial eruptions.
Katla has no obvious degassing vents or areas, or visible gas plumes. Presence of subglacial activity is man-
ifested by 20 ice cauldrons, which are 10- to 50-m deep depressions in the glacier surface (Figure 1) caused by
geothermal melting of the glacier base. Geothermal melt water escapes through the glacier drainage systems
and is periodically ushed out from the outlet rivers (Figure 1). The number, size, and shape of Katla s ice caul-
drons and the activity of the outlet rivers change over time as the subglacial system is highly dynamic
(Guðmundsson et al., 2007), likely inuenced both by the state of the volcanic system, and short- and long-term
variations in weather and climate. The smell of hydrogen sulde (H
2
S) is commonly reported near the outlet
rivers, in particular during major and minor jökulhlaups (Bergsson, 2016). Conversely, there are no known reports
of visible gas plumes or gas smell in the vicinity of the ice cauldrons. A DOAS UV spectrometer installed on the
anks of Katla since July 2017 has never detected sulfur dioxide (SO
2
)(IcelandicMetOfce monitoring data).
The only eruption of Katla where gas release has been estimated using the petrological method is the Eldgjá
ood basalt eruption 93440 C.E. (Thordarson et al., 2003). Its current gas emission rate has not been
Figure 1. (a) Map and (b) photograph of Katla. The map shows the outlines of the subglacial caldera and locations of glacier river outlets (n = 8), ice cauldrons (n = 20),
Goðabunga rise (God), and Austmannsbunga rise (Aust). For model simulations of the gas source, the 20 ice cauldrons were combined into seven clusters (AG).
The photograph, taken in November 2017, shows ice cauldrons 10 and 11 (K10 and K11, respectively) and Goðabunga rise. The cauldrons are several hundreds of
meters in diameter. The summit of the neighboring Eyjafjalljökull volcano is seen behind the Katla caldera.
10.1029/2018GL079096
Geophysical Research Letters
ILYINSKAYA ET AL. 10,334

quantied. Here we measured Katlas gas emissions from an aircraft in October 2016 and October 2017.
This work builds on previous airborne measurements of CO
2
-rich plumes in other countries using in situ
sensors (Delgado et al., 1998; Doukas & McGee, 2007; Gerlach et al., 1999, 1997; Werner et al., 2006, 2008,
2012, 2013) and serves as a proof-of-concept for monitoring gas emissions from other Icelandic
volcanic systems.
2. Methods
2.1. Airborne Observations
The airborne observations were made using the atmospheric research aircraft (a highly modied BAE-146
aircraft) of the Facility for Airborne Atmospheric Measurements (http://www.faam.ac.uk). Details about the
instrumentation are in Text S1 in the supporting information. Flight paths were selected based on the preva-
lent wind direction in order to obtain downwind measurements of active volcanoes. Low-altitude cloud dis-
tribution and topography inuenced the ight path planning for safety reasons. No ights traversing the
subglacial caldera were possible in 2016 or 2017 due to cloud cover over the glacier. The full tracks of the
ights reported in this paper are shown in Figure S1 in the supporting information.
2.2. Gas Source Modeling
In order to identify the source of the excess CO
2
, we applied two approaches. The rst was to use back-
trajectories based on simple, low-resolution forecast wind elds; we used the Hybrid Single-Particle
Lagrangian Integrated Trajectory (HYSPLIT) Lagrangian dispersion model driven by GFS forecast winds (full
details about the model in Text S1). The second involved simulating the effects of a variety of plausible
sources within a very high resolution numerical weather prediction model (Weather Research and
Forecasting model [WRF]; full details about the model Text S1) and comparing the distribution of dispersed
gases within the model with the observations. HYSPLIT was run from numerous measurement points along
the aircraft track for 12 hr back in time in order to determine which trajectories coincided with likely sources.
The relatively long run time was chosen so that there were no initial constraints on the gas source within
Iceland (e.g., other volcanic systems and anthropogenic activities). Results of HYSPLIT are included in support-
ing information (Figure S2). For the sources in the WRF simulations we initially used the 32 volcanic systems in
Iceland (Figure S1) and ran the WRF model with CO
2
as a passive tracer. This conrmed unequivocally that the
source was in the region of Katla, leading us to make further measurement ights in 2017, and more detailed
simulations of the Katla region in order to identify the source of the gas. For these simulations, we specied as
potential sources 8 glacier outlet rivers from Katla, 20 ice cauldrons within the caldera that were combined
into 7 cauldron clusters (AG), and Goðabunga rise (a location of long-term seismic activity on the volcanos
west ank), giving a total of 16 sources (Figure 1). All sources were treated as a point release of a dense gas
with a specied emission rate (full details in Text S1). For most of the simulated cases, HYSPLIT and WRF indi-
cated the same source locations; notable differences are described in section 3.
2.3. Gas Emission Rate Calculations
As the exact location and number of the degassing sources within the large glacier (590 km
2
) overlying Katla
were unknown, the calculation of the CO
2
emission rate (ux) presented a challenge not previously
reported in studies using airborne measurements. We calculated the CO
2
ux using two independent
methods, direct calculations and model simulations. The model simulations provided an independent means
of mass ux estimation and hence a corroboration of the principal ndings of the paper.
The rst method was a direct calculation of the measured mass ux by integration of interpolations of the
measured wind and CO
2
concentration elds (we used two different interpolation techniques). The interpo-
lation techniques were inverse distance weighting (IDW in Table 1) for all of the ights and tting of a
Gaussian plume dispersion model (Gaussian in Table 1). The Gaussian method provided an independent ux
estimate in addition to IDW. Several restrictions on its use (the requirement for a Gaussian plume, the need
for wind speeds above 5 m/s, and the wind direction and ight track alignment to be perpendicular) meant
that the Gaussian method could only be used for ight B989 (Table 1). It is included here for completeness.
See Text S1 for further details about both interpolation techniques.
Motivated by the large emission rates given by IDW and Gaussian calculations (1120 kt/d of CO
2
, Table 1), we
designed the second method of estimating emission rates using a state-of-the-art numerical model, WRF (the
10.1029/2018GL079096
Geophysical Research Letters
ILYINSKAYA ET AL. 10,335

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BookDOI
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Abstract: Volcanism and metamorphism are the principal geologic processes that drive carbon transfer from the interior of Earth to the surface reservoir. Input of carbon to the surface reservoir through volcanic degassing is balanced by removal through silicate weathering and the subduction of carbon-bearing marine deposits over million-year timescales. The magnitude of the volcanic carbon flux is thus of fundamental importance for stabilization of atmospheric CO2 and for long-term climate. It is likely that the “deep” carbon reservoir far exceeds the size of the surface reservoir in terms of mass; more than 99% of Earth’s carbonmay reside in the core, mantle, and crust. The relatively high flux of volcanic carbon to the surface reservoir, combined with the reservoir’s small size, results in a short residence time for carbon in the ocean–atmosphere–biosphere system (~200 ka). The implication is that changes in the flux of volcanic carbon can affect the climate and ultimately the habitability of the planet on geologic timescales. In order to understand this delicate balance, we must first quantify the current volcanic flux of carbon to the atmosphere and understand the factors that control this flux. The three most abundant magmatic volatiles are water (H2O), carbon dioxide (CO2), and sulfur (S), with CO2 being the least soluble in silicate melts. 8 For this reason, it is not only Earth’s active volcanoes that are a source of magmatic CO2, but also numerous inactive volcanoes with magma bodies present at depth in the crust that contribute to the carbon emissions (Figure 8.1). Emissions from active volcanoes are released through crater fumaroles and open vents to form visible volcanic plumes, but diffuse degassing and degassing through springs on the volcano flanks also contribute to the total flux of carbon from a volcano. Plume gas emissions typically dominate over flank gas emissions and are highest during periods of eruptive activity. Due to the hazard associated with eruptions and the value of volcanic gas monitoring to aid in eruption forecasting, much of our knowledge about the degassing of volcanic systems comes from active volcanoes, and typically during periods of unrest. At less active and dormant (i.e. inactive) volcanoes, magmatic emissions of CO2 are less obvious. CO2 emissions are typically highest in thermal areas where gases are emitted through small fumaroles, soils, and fractures as diffuse degassing and through hot and cold

44 citations


Journal ArticleDOI
Abstract: 14 The existence of stabilizing feedbacks on Earth is generally thought to be necessary for the persistence of 15 liquid water and life. Earth’s atmospheric composition appears to have adjusted to the gradual increase in 16 solar luminosity over time, resulting in persistently habitable surface temperatures. With limited exceptions, 17 the Earth system recovered rapidly from climatic perturbations. Carbon dioxide (CO2) regulation via negative 18 feedbacks within the coupled global carbon-silica cycles are classically viewed as the main processes giving 19 rise to climate stability on Earth. Here we review the long-term global carbon cycle budget and how the 20 processes modulating Earth’s climate system have evolved over time. Specifically, we focus on the relative 21 roles that shifts in carbon sources and sinks have played in driving long-term changes in atmospheric pCO2. 22 We make a case that marine processes are an important component of the canonical silicate weathering 23 feedback, and have played a much more important role in pCO2 regulation than traditionally imagined. The 24 weathering of marine sediments and off-axis basalt alteration are major carbon sinks. However, this sink 25 was potentially dampened during Earth’s early history when oceans had higher levels of dissolved silicon 26 (Si), iron (Fe) and magnesium (Mg), and instead likely fostered more extensive reverse weathering—which in 27 turn fostered higher ocean-atmosphere CO2. 28 29

32 citations



Journal ArticleDOI
Abstract: Geological CO2 degassing is a fundamental Earth process but still quite poorly understood, since a thorough quantification with conventional measurement techniques is challenging. Optical remote sensing techniques have the potential to extend conventional measurement capabilities, enabling new insights into processes related to Earth’s CO2 degassing. This article provides an integrated and pragmatic overview of existing and future remote sensing approaches suitable for geological CO2 quantification and connects results from instrument research in optical remote sensing with possible applications in the Earth sciences. The paper aims to provide intercomparison by means of key parameters of very different remote sensing approaches. One of these parameters is the minimum detectable CO2 flux, which is estimated for each remote sensing method herein. This may be used to identify a remote sensing platform for a specific Earth science problem related to CO2 degassing. Six such prominent Earth science problems are detailed. Remote sensing technology for extraterrestrial CO2 degassing is briefly examined. With respect to established in situ measurements, the main benefits of remote sensing include a safe measurement distance, spatially inclusive probing and swift measurements, while the main shortcomings include a generally lower measurement precision and the lack of commercially available turnkey solutions. While all six Earth science problems examined in this review will benefit to some extent from CO2 remote sensing, remote sensing is unlikely to replace conventional in situ probing entirely in the near future, but can be seen as complementary to conventional measurement approaches. Earth science problems that could immediately benefit from CO2 remote sensing include a comprehensive survey of the significant but highly uncertain CO2 flux of the East African Rift System, comparing volcanic CO2 concentrations from satellite borne remote sensing with ground-based remote sensing, and integration of CO2 remote sensing data into automated volcanic unrest prediction.

20 citations


Journal ArticleDOI
Abstract: Carbon is a key control on the surface chemistry and climate of Earth. Significant volumes of carbon are input to the oceans and atmosphere from deep Earth in the form of degassed CO2 and are returned to large carbon reservoirs in the mantle via subduction or burial. Different tectonic settings (e.g., volcanic arcs, mid-ocean ridges, and continental rifts) emit fluxes of CO2 that are temporally and spatially variable, and together they represent a first-order control on carbon outgassing from the deep Earth. A change in the relative importance of different tectonic settings throughout Earth’s history has therefore played a key role in balancing the deep carbon cycle on geological timescales. Over the past 10 years the Deep Carbon Observatory has made enormous progress in constraining estimates of carbon outgassing flux at different tectonic settings. Using plate boundary evolution modeling and our understanding of present-day carbon fluxes, we develop time series of carbon fluxes into and out of the Earth’s interior through the past 200 million years. We highlight the increasing importance of carbonate-intersecting subduction zones over time to carbon outgassing, and the possible dominance of carbon outgassing at continental rift zones, which leads to maxima in outgassing at 130 and 15 Ma. To a first-order, carbon outgassing since 200 Ma may be net positive, averaging ∼50 Mt C yr–1 more than the ingassing flux at subduction zones. Our net outgassing curve is poorly correlated with atmospheric CO2, implying that surface carbon cycling processes play a significant role in modulating carbon concentrations and/or there is a long-term crustal or lithospheric storage of carbon which modulates the outgassing flux. Our results highlight the large uncertainties that exist in reconstructing the corresponding in- and outgassing fluxes of carbon. Our synthesis summarizes our current understanding of fluxes at tectonic settings and their influence on atmospheric CO2, and provides a framework for future research into Earth’s deep carbon cycling, both today and in the past.

19 citations


References
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Journal ArticleDOI
Abstract: Emissions of CO2 are the main contributor to anthropogenic climate change. Here we present updated information on their present and near-future estimates. We calculate that global CO2 emissions from fossil fuel burning decreased by 1.3% in 2009 owing to the global financial and economic crisis that started in 2008; this is half the decrease anticipated a year ago1. If economic growth proceeds as expected2, emissions are projected to increase by more than 3% in 2010, approaching the high emissions growth rates that were observed from 2000 to 20081, 3, 4. We estimate that recent CO2 emissions from deforestation and other land-use changes (LUCs) have declined compared with the 1990s, primarily because of reduced rates of deforestation in the tropics5 and a smaller contribution owing to forest regrowth elsewhere.

526 citations


Journal ArticleDOI
Abstract: Over long periods of time (~Ma), we may consider the oceans, atmosphere and biosphere as a single exospheric reservoir for CO2. The geological carbon cycle describes the inputs to this exosphere from mantle degassing, metamorphism of subducted carbonates and outputs from weathering of aluminosilicate rocks (Walker et al. 1981). A feedback mechanism relates the weathering rate with the amount of CO2 in the atmosphere via the greenhouse effect (e.g., Wang et al. 1976). An increase in atmospheric CO2 concentrations induces higher temperatures, leading to higher rates of weathering, which draw down atmospheric CO2 concentrations (Berner 1991). Atmospheric CO2 concentrations are therefore stabilized over long timescales by this feedback mechanism (Zeebe and Caldeira 2008). This process may have played a role (Feulner et al. 2012) in stabilizing temperatures on Earth while solar radiation steadily increased due to stellar evolution (Bahcall et al. 2001). In this context the role of CO2 degassing from the Earth is clearly fundamental to the stability of the climate, and therefore to life on Earth. Notwithstanding this importance, the flux of CO2 from the Earth is poorly constrained. The uncertainty in our knowledge of this critical input into the geological carbon cycle led Berner and Lagasa (1989) to state that it is the most vexing problem facing us in understanding that cycle. Notwithstanding the uncertainties in our understanding of CO2 degassing from Earth, it is clear that these natural emissions were recently dwarfed by anthropogenic emissions, which have rapidly increased since industrialization began on a large scale in the 18th century, leading to a rapid increase in atmospheric CO2 concentrations. While atmospheric CO2 concentrations have varied between 190–280 ppm for the last 400,000 years (Zeebe and Caldeira 2008), human activity has produced a remarkable increase …

268 citations



Journal ArticleDOI
Abstract: The supply of magma to Kīlauea Volcano, Hawai‘i, was thought to have been steady over the past decades. Measurements of deformation, gas emissions, seismicity and lava composition and temperatures show that instead magma supply from the mantle doubled in 2003–2007, implying that hotspots can provide varying amounts of magma over just a few years.

146 citations


Journal ArticleDOI
Abstract: The Katla volcano in Iceland is characterized by subglacial explosive eruptions of Fe–Ti basalt composition. Although the nature and products of historical Katla eruptions (i.e. over the last 1,100 years) at the volcano is well-documented, the long term evolution of Katla’s volcanic activity and magma production is less well known. A study of the tephra stratigraphy from a composite soil section to the east of the volcano has been undertaken with emphasis on the prehistoric deposits. The section records ∼8,400 years of explosive activity at Katla volcano and includes 208 tephra layers of which 126 samples were analysed for major-element composition. The age of individual Katla layers was calculated using soil accumulation rates (SAR) derived from soil thicknesses between 14C-dated marker tephra layers. Temporal variations in major-element compositions of the basaltic tephra divide the ∼8,400-year record into eight intervals with durations of 510–1,750 years. Concentrations of incompatible elements (e.g. K2O) in individual intervals reveal changes that are characterized as constant, irregular, and increasing. These variations in incompatible elements correlate with changes in other major-element concentrations and suggest that the magmatic evolution of the basalts beneath Katla is primarily controlled by fractional crystallisation. In addition, binary mixing between a basaltic component and a silicic melt is inferred for several tephra layers of intermediate composition. Small to moderate eruptions of silicic tephra (SILK) occur throughout the Holocene. However, these events do not appear to exhibit strong influence on the magmatic evolution of the basalts. Nevertheless, peaks in the frequency of basaltic and silicic eruptions are contemporaneous. The observed pattern of change in tephra composition within individual time intervals suggests different conditions in the plumbing system beneath Katla volcano. At present, the cause of change of the magma plumbing system is not clear, but might be related to eruptions of eight known Holocene lavas around the volcano. Two cycles are observed throughout the Holocene, each involving three stages of plumbing system evolution. A cycle begins with an interval characterized by simple plumbing system, as indicated by uniform major element compositions. This is followed by an interval of sill and dyke system, as depicted by irregular temporal variations in major element compositions. This stage eventually leads to a formation of a magma chamber, represented by an interval with increasing concentrations of incompatible elements with time. The eruption frequency within the cycle increases from the stage of a simple plumbing system to the sill and dyke complex stage and then drops again during magma chamber stage. In accordance with this model, Katla volcano is at present in the first interval (i.e. simple plumbing system) of the third cycle because the activity in historical time has been characterized by uniform magma composition and relatively low eruption frequency.

123 citations


Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "Globally significant co2 emissions from katla, a subglacial volcano in iceland" ?

Through high-precision airborne measurements and atmospheric dispersion modeling, the authors show that Katla, a highly hazardous subglacial volcano that last erupted 100 years ago, is one of the largest volcanic sources of CO2 on Earth, releasing up to 4 % of total global volcanic emissions. This is significant in a context of a growing awareness that natural CO2 sources have to be more accurately quantified in climate assessments, and the authors recommend urgent investigations of other subglacial volcanoes worldwide.