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

TL;DR: In this article, the authors 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.
Abstract: Volcanoes 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

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
Published in:
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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Journal ArticleDOI
TL;DR: In this article, the authors review the long-term global carbon cycle budget and how the processes modulating Earth's climate system have evolved over time, focusing on the relative roles that shifts in carbon sources and sinks have played in driving longterm changes in atmospheric CO2.
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

68 citations

Journal ArticleDOI
TL;DR: In this article, a time series of carbon fluxes into and out of the Earth's interior through the past 200 million years is used to compare the relative importance of different tectonic settings throughout Earth's history to carbon outgassing.
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.

37 citations

Journal ArticleDOI
TL;DR: In this article, a detailed description of the processes that affect soil CO2 emissions and outline their impacts as functions of different features of the measurement sites are provided. But, the authors do not consider the impact of these processes on the monitoring data.

31 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a detailed study of spatial variations on the diffuse emission of carbon dioxide (CO2) and hydrogen sulfide (H2S) from Hengill volcanic system, Iceland was performed at 752 sampling sites and ranged from nondetectable to 17,666 and 722 g m−2 day−1.
Abstract: We report the first detailed study of spatial variations on the diffuse emission of carbon dioxide (CO2) and hydrogen sulfide (H2S) from Hengill volcanic system, Iceland. Soil CO2 and H2S efflux measurements were performed at 752 sampling sites and ranged from nondetectable to 17,666 and 722 g m−2 day−1, respectively. The soil temperature was measured at each sampling site and used to evaluate the heat flow. The chemical composition of soil gases sampled at selected sampling sites during this study shows they result from a mixing process between deep volcanic/hydrothermal component and air. Most of the diffuse CO2 degassing is observed close to areas where active thermal manifestations occur, northeast flank of the Hengill central volcano close to the Nesjavellir power plant, suggesting a diffuse degassing structure with a SSW–NNE trend, overlapping main fissure zone and indicating a structural control of the degassing process. On the other hand, H2S efflux values are in general very low or negligible along the study area, except those observed at the northeast flank of the Hengill central volcano, where anomalously high CO2 efflux and soil temperatures were also measured. The total diffuse CO2 emission estimated for this volcanic system was about 1,526 ± 160 t day−1 of which 453 t day−1 (29.7 %) are of volcanic/hydrothermal origin. To calculate the steam discharge associated with the volcanic/hydrothermal CO2 output, we used the average H2O/CO2 mass ratio from 12 fumarole samples equal to 88.6 (range, 9.4–240.2) as a representative value of the H2O/CO2 mass ratios for Hengill fumarole steam. The resulting estimate of the steam flow associated with the gas flux is equal to 40,154 t day−1. The condensation of this steam results in thermal energy release for Helgill volcanic system of 1.07 × 1014 J day−1 or to a total heat flow of 1,237 MWt.

55 citations

Journal ArticleDOI
TL;DR: Tazieff et al. as mentioned in this paper studied heat and mass transfer rates at the Niragongo lava lake during two expeditions directed by H. Tazieef in 1959 and 1972, and found that heat is transferred to the surface of the lake by the movement of lava; gas discharge is a result and not the cause of convection.

55 citations

Journal ArticleDOI
TL;DR: In this article, the authors report CO2, SO2, and H2S emission rates and C/S ratios during the five months leading up to the 2009 eruption of Redoubt Volcano, Alaska.
Abstract: [1] We report CO2, SO2, and H2S emission rates and C/S ratios during the five months leading up to the 2009 eruption of Redoubt Volcano, Alaska. CO2emission rates up to 9018 t/d and C/S ratios ≥30 measured in the months prior to the eruption were critical for fully informed forecasting efforts. Observations of ice-melt rates, meltwater discharge, and water chemistry suggest that surface waters represented drainage from surficial, perched reservoirs of condensed magmatic steam and glacial meltwater. These fluids scrubbed only a few hundred tonnes/day of SO2, not the >2100 t/d SO2expected from degassing of magma in the mid- to upper crust (3–6.5 km), where petrologic analysis shows the final magmatic equilibration occurred. All data are consistent with upflow of a CO2-rich magmatic gas for at least 5 months prior to eruption, and minimal scrubbing of SO2by near-surface groundwater. The high C/S ratios observed could reflect bulk degassing of mid-crustal magma followed by nearly complete loss of SO2in a deep magmatic-hydrothermal system. Alternatively, high C/S ratios could be attributed to decompressional degassing of low silica andesitic magma that intruded into the mid-crust in the 5 months prior to eruption, thereby mobilizing the pre-existing high silica andesite magma or mush in this region. The latter scenario is supported by several lines of evidence, including deep long-period earthquakes (−28 to −32 km) prior to and during the eruption, and far-field deformation following the onset of eruptive activity.

49 citations

Journal ArticleDOI
TL;DR: In this article, the first airborne detection of CO2 degassing from diffuse volcanic sources was reported, which offers a rapid alternative for monitoring CO2 emission rates at Mammoth Mountain.
Abstract: We report the first airborne detection of CO2 degassing from diffuse volcanic sources. Airborne measurement of diffuse CO2 degassing offers a rapid alternative for monitoring CO2 emission rates at Mammoth Mountain. CO2 concentrations, temperatures, and barometric pressures were measured at ∼2,500 GPS-referenced locations during a one-hour, eleven-orbit survey of air around Mammoth Mountain at ∼3 km from the summit and altitudes of 2,895–3,657 m. A volcanic CO2 anomaly 4–5 km across with CO2 levels ∼1 ppm above background was revealed downwind of tree-kill areas. It contained a 1-km core with concentrations exceeding background by >3 ppm. Emission rates of ∼250 t d−1 are indicated. Orographic winds may play a key role in transporting the diffusely degassed CO2 upslope to elevations where it is lofted into the regional wind system.

46 citations

Journal ArticleDOI
TL;DR: In this paper, GPS measurements on nunataks exposed on the caldera edge revealed steady inflation of the volcano and showed uplift and horizontal displacement of the nuntatak benchmarks at a rate of up to 2 cm a−1.
Abstract: Katla is one of Iceland's most active volcanoes with at least 20 eruptions in the last 1100 years. The volcano is covered mostly by the Mýrdalsjokull ice cap; consequently, Katla eruptions are phreato-magmatic and are capable of producing jokulhlaups. A jokulhlaup in July 1999, preceded by an episode of continuous seismic tremor, was the first sign of renewed magma movement under the volcano since 1955. Using seismic and geodetic observations, and insights into geothermal activity from ice-surface observations, we analyze this period of unrest and assess the present state of Katla volcano. From 1999 to 2004, GPS measurements on nunataks exposed on the caldera edge revealed steady inflation of the volcano. Our measurements show uplift and horizontal displacement of the nuntatak benchmarks at a rate of up to 2 cm a−1, together with horizontal displacement of far-field stations (>11 km) at about 0.5 cm a−1 away from the caldera centre. Using a point-source model, these data place the center of the magma chamber at 4.9 km depth beneath the northern part of the caldera. However, this depth may be overestimated because of a progressive decrease in the mass of the overlying ice cap. The depth may be only 2–3 km. About 0.01 km3 of magma has accumulated between 1999 and 2004; this value is considerably less than the estimated 1 km3 of material erupted during the last eruption of Katla in 1918. Presently, rates of crustal deformation and earthquake activity are considerably less than observed between 1999 and 2004; nonetheless, the volcano remains in an agitated state.

42 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.