Seafloor warming and Arctic gas hydrates: Overview on current

Seafloor warming and Arctic gas hydrates:
Overview on current research activities
Tina Treude, Lihua Liu, Stefan Krause, Stephanie Reischke, Julia Hommer
Future Ocean Junior Research Group “Seafloor Warming”
Leibniz Institute of Marine Sciences (IFM-GEOMAR), Wischhofstr. 1-3, 24148 Kiel, Germany, [email protected]
Introduction
Arctic regions, both terrestrial and submarine, harbor large amounts of methane
currently locked up in permafrost and in the form of gas hydrates. As most climate
models predict a rapid increase in Arctic air and surface-water temperatures within
the next few decades, the release of methane from these reservoirs is likely to
increase due to permafrost melting and gas hydrates destabilization. Emissions of
this very potent greenhouse gas into the atmosphere could further boost the climate
disaster. Recent findings on increased methane emissions from Arctic regions
galvanized the scientific community and led to a sequence of actions within the last
months including workshops, proposal submissions, and planning of expeditions.
Fig. 1. Molecular structure of gas
hydrates. Blue: water molecules,
green: gas molecules
The Future Ocean Junior Research Group "Seafloor Warming" headed by
Tina Treude is currently involved in several of these actions, including an international
workshop on arctic gas hydrates that was hosted by the NIOZ in Februray 2009. The workshop
was co-financed by the Intergrated School of Ocean Sciences (ISOS).
Dissolution
and
formation
of authigenic
Dissolution
and
formation
of authige
connected
to to
microbial
methanot
connected
microbial
methan
Fig. 2. Parameters controllinggas hydrate stability
Stefan
Krause,
Giovanni
Aloisi,
Volker
Liebetrau,
Tina TT
Stefan
Krause,
Giovanni
Aloisi,
Volker
Liebetrau,
Fig. 3. Gas release after dissociation
of gas hydrate
Fields of Research
Leibniz
Institute
of Marine
Sciences
(IFM-GEOMAR),
JuniorJunior
Research
GroupGro
“S
Leibniz
Institute
of Marine
Sciences
(IFM-GEOMAR),
Research
Numerical Modelling
Results
and Discussion
Introduction
Results
and Discussi
Introduction
When the temperature at the sea floor rises, gas hydrate stored in the marine sediment
The oxidation
of methane
by benthic
largely affects
the
The oxidation
of methane
bymicroorgamisms
benthic microorgamisms
largely
affects the
The
of pH in the controls
illustrat
pH
The development
of pH in the
con
pH development
system may become unstable and dissociate. In this conext several important questions
phase and the
headspace
1 a). CO(Fig.
phase
and the(Fig.
headspace
a)
seafloor carbonate
system atsystem
marineatmethane
seep locations.
seafloor carbonate
marine methane
seep locations.
2 loss1fro
in pH (from 6.8
to ~(from
8.2) during
3 days.
in pH
6.8 to ~the
8.2)first
during
the
arrise. How fast will gas hydrate dissociate? How much methane will escape from
(0 to 3 days),(0
pHtovalues
fluctuated
6.3
3 days),
pH valuesbetween
fluctuated
, CaCO3,
The Anaerobic
OxidationOxidation
of Methane
(AOM) facilitates
production
of CaCO3of
The Anaerobic
of Methane
(AOM) facilitates
production
resulting from
simultaneous
microbial and
phy
resulting
from simultaneous
micro
the microbial filter?
subsequent phase
od thephase
experiment
mo
subsequent
od the were
experim
withdrawing
carbon from
the from
Dissolved
InorganicInorganic
Carbon (DIC)
pool.
withdrawing
carbon
the Dissolved
Carbon
(DIC) pool.
a
microbes and
equilibrium
thebetwee
liquide
microbes
and between
equilibrium
To answer these questions a Reactive Transport Model was developed, which simulates
production eventually
to pH decrease
in t
productionlead
eventually
lead to pH
Net reaction
AOM: of AOM:
exceeded. exceeded.
reaction
the dissociation of gas hydrate and related biogeochemical processes for a time period
of Net of
22- CH4 + SOCH
HS+ HCO
+ H23O + HCO3
b
4 4 + SO4 HS + H2O
100 years. The results indicate:
(Fig. 1c) (TA)
remained
constant
over
Alkalinity Alkalinity
Alkalinity
(Fig. 1c)
remained
c
Alkalinity(TA)
-
Aerobic oxidation
of methane
is observed
in the topinlayer
of seep
Aerobic
of methane
is observed
the top
layersediments.
of seep sediments.
Decrease of seafloor warming caused by the dissociation of gas hydrates in the sediment
(Fig. oxidation
4a)
Here, specialized
proteobacteria
oxidize methane
with oxygen
CO2.
proteobacteria
oxidize methane
withproducing
oxygen producing
CO2.
Melting of hydrates within the top 30 m of the sediment (10 % of total hydrates, Fig.
4b)Here, specialized
Melting begins after ~30 years (increase in gas volume fraction, Fig. 4c)
Net reaction
aerobicofoxidation
of methane:
Net of
reaction
aerobic oxidation
of methane:
Ca
Approximately 2 % of the released methane will be comsumed by Anaerobic Oxidation
CH4 + 2of
OCH
2 H22O + CO
c 2
2 4 + 2 O22 H2O + CO
Methane (AOM) (Fig. 4d, 4e).
e
Outlook:
The model will be further refined and applied to forcast future methane emissions
Artic seafloor.
It is assumed
that AOMthat
hasAOM
no pronounced
effect on effect
porewater
pH. However,
It is assumed
has no pronounced
on porewater
pH. However,
the aerobic
is suspected
to decrease
local pH by
COpH
This
thepathway
aerobic pathway
is suspected
to decrease
local
by CO2 production.
This
2 production.
to considerable
extends extends
might facilitate
dissolution
of present
to considerable
might facilitate
dissolution
ofCaCO
present
CaCO3 structures
3 structures
increasing
the DIC concentration
and thus,and
reintroducing
stored carbon
the to the
increasing
the DIC concentration
thus, reintroducing
storedtocarbon
atHydrosphere.
the Hydrosphere.
Coauthors: Klaus Wallmann, Tomas Feseker
a
1a
1a
b
1b
pH-C
ntro
o
l
pH-Bacteria
c
pH-Bacteria
8.7
E1
E1
8.2
8.2
8.2
8.2
E2
E2
C1
C1
7.2
C2
C2
6.7
6.7
C3
C3
6.2
6.2
7.03.5
5000
0
1d
4.0
3.0
2.0
1.0
10.5
7.0
10000
5000
days
minutes
15000
C4
10.5
15000
10000
1c
5.0
C1
C1
4.0
C2
C2
3.0
C3
C3
2.0
7.03.5
5000
0
C4
15000
10.5
7.0
10000
5000
days
minutes
4.0
C4
Ca2+ (mM)
3.0
2.0
1.0
0.0
0
0
2.0
15000
7.03.5
5000
0
10000
5000
days
minutes
1.0
3.0
2.0
1.0
C2
C2
C3
C3
C4
15000
C4
10.5
7.0
15000
10000
days
minutes
10.5
E1
E2
E2
E4
15000
3.50
0
E1
E3
0.0
0
1.0
3.50
2.0
1f
C1
7.03.5
5000
0
(i) How do changes in methane flux affect the activity of methanotrophic microbes
(ii) Could increases in methane fluxes lead to higher methane emissions?
Fig. 3: Pre-experimental
surface
Fig. 3: Pre-experimental
surface
E3
15000
10.57.0
10000
5000
E4
10.5
15000
10000
15000
days
minutes
1fCa2+ concentration-Bacteria
Ca2+ concentration-Bacteria
4.0
4.0
3.0
3.0
2.0
1.0
0.0
15000
0
0
Fig. 4: Surface without
bacteria
Fig. 4: Surface
wit
2.0
1.0
E1
E1
E2
E2
E3
E4
15000
0.0
3.50
7.03.5
5000
0
days
minutes
E3
15000
10.57.0
10000
5000
15000
10000
days
minutes
E4
Typical surface
structure
calcite crystal
fro
Typical
surfaceofstructure
of calcit
experimentexperiment
with spatialwith
alterations
due to m
spatial alteratio
facilitated carbonate
facilitated dissolution.
carbonate dissolution
10.5
d
15000
Fig. 1a-f: Results
control
group
bacteria
Fig.of1a-f:
Results
of and
control
groupexperiment
and bacteria experiment
Fig. 5a-d. a+b: Results of carbonate dissolution experiment,
c+d: SEM images of intact (c) and etched (d) carbonates
Material
and Methods
Material
and Methods
Conclusions
Conclusions
Microbially
facilitatedfacilitated
aerobic oxidation
of
Microbially
aerobic oxi
The aerobic
bacterium
Methylosinus
trichosporium
(Fig. 2) was
Themethanotrophic
aerobic methanotrophic
bacterium
Methylosinus
trichosporium
(Fig. 2) was
has a negative
effect on effect
the stab
has a negative
on
used in this
experiment.
The experiment
was conducted
in sealed in
0.5sealed
l glass0.5 l glass interface interface
used
in this experiment.
The experiment
was conducted
during aero
CO2 produced
du
- Theof
amount
of CO2 produced
containers
with 0.25with
l liquid
0.32 and
l headspace
each (4 controls,
4 bacteria4 bacteria - The amount
containers
0.25and
l liquid
0.32 l headspace
each (4acontrols,
carbonate
buffer capacity,
ca
exceed
the carbonate
buffer cap
experiment
replicates).
SterilizedSterilized
calcite powder
g per container)
was usedwas
as used as exceed the
experiment
replicates).
calcite(3
powder
(3 g per container)
. AsCaCO
a conse
the saturation
state of CaCO
the saturation
state3of
3. A
carbonate
source. Liquids
controls
bacteria
had identical
ion
carbonate
source.ofLiquids
of and
controls
and experiments
bacteria experiments
had identical
ion
2+ and
2
ions.
by
increase
in
alkalinity
and
Ca
by
increase
in
alkalinity
Ca
was
set 3towas
1 set to 1
composition
resembling
seawater.seawater.
Initial saturation
state for CaCO
composition
resembling
Initial saturation
state 3for
CaCO
- Aerobic-oxidation
of methane
could enhc
Aerobic oxidation
of methane
to inhibitto
physical
initial pHinitial
was ~pH
6.8.was
The~headspace
was sealed
and
inhibit dissolution,
physical dissolution,
6.8. The headspace
was
sealed and
column atcolumn
places at
with
increased
methan
places
with increased
gassed with
Air : with
Methane
(1:1) to 2 (1:1)
bar. During
experiment
exchangeexchange
betweenbetween
gassed
Air : Methane
to 2 bar.the
During
the experiment
Arctic, where
gas
hydrates
are exspected
Arctic,
where
gas hydrates
are e
headspace
and atmosphere
was prevented.
headspace
and atmosphere
was prevented.
In cooperation with the SFB 574 a flow-through system is currently developed
to gain further insights into the mechanisms of biogeochemical processes in the
sediment connected to methane transport (Fig 6a). The system will enable
manipulations of a broad range of geochemical and flow parameters in
sediment cores (Fig. 6b). A set of different methods, e.g. microsenor measurements (Fig. 6c),
Liquids were
repeatedly
sampled sampled
for:
Liquids
were repeatedly
for:
porewater extractions and analyzes, will be applied.
Core questions are:
15000
days
minutes
days
minutes
C1
10.5
15000
10000
4.0
days
minutes
3.0
0.0
3.0
15000
10.57.0
E4
5.0
4.0
0.0
10.5
15000
10000
4.0
7.03.5
10000
5000
Surface structure
calc
Surfaceofstruc
pre-experimental
morp
pre-experime
E3
15000
Alkalinity-Bacteria
Alkalinity-Bacteria
5.0
1.0
3.50
0
0
7.2
6.7
6.2
5000
0
1c
E4
15000
days
minutes
Alkalinity-Control
Alkalinity-Control
0.0
7.7
days
minutes
15000
E3
3.50
0
0
15000
Alkalinity (mM)
3.50
0
5.0
0.0
15000
7.2
6.7
6.2
Ca2+ (mM)
0
C4
Alkalinity (mM)
7.2
7.7
pH
7.7
Ca2+ (mM)
pH
7.7
pH
8.7
1eCa2+ concentration-Control
Ca2+ concentration-Control
Ca2+ (mM)
1b
-pH, analyzed
with microsensores
-pH, analyzed
with microsensores
c (Fig. 6) (Fig. 6)
-Alkalinity-Alkalinity
(TA), analyzed
by Titration
(TA), analyzed
by Titration
-Ca2+ concentration,
analyzedanalyzed
with ICP with ICP
-Ca2+ concentration,
Outlook
Outlook
Future investigations
will focuswill
on:focus o
Future investigations
Microsensor
Microsensor
- Microbial
carbonate
precipitation
during
- Microbial
carbonate
precipitati
- Carbonate
nucleation
details ondetails
the cell
- Carbonate
nucleation
on
?,
electrodeelectrode
- Identification
of seafloor
and o
- Identification
of warming
seafloor warmi
Powder surface
was
Powdermorphological
surface morphological
was
dissolution
of car
induced precipitation/
dissoluti
Sample vessel
Sample vessel induced precipitation/
analyzedanalyzed
by Scanning
Electron Microscopy
(SEM). (SEM).
by Scanning
Electron Microscopy
- Numerical
modelling
of relevant
- Numerical
modelling
of biogeo
relevan
Fig. 6: Rapid pH-measurement
with a micro sensor
Fig. 6: Rapid pH-measurement
with a micro sensor
ReferenceReferenceb
Gained data will be used in numerical reaction models simulating gas hydrate dissociation (see above).
Stefan Stefan
Krause Krause
Contact
Contact
Future Future
Ocean, Ocean,
Junior Reseach
Group "Seafloor
Warming"
Junior Reseach
Group "Seafloor
Warming"
Coauthor: Peter Linke
Fig. 6a: Schematic drawing of flow-through system, b: Sediment core liners used in the
IfM-GEOMAR,
Wischhofstr.
1-3,(Copyright
24148
IfM-GEOMAR,
Wischhofstr.
1-3,byKiel
24148
system, c:
Microsensors
Unisense)Kiel
[email protected]
[email protected]
www.ozean-der-zukunft.de
www.ozean-der-zukunft.de
Upcoming Expeditions
Beaufort Sea Expedition, September 2009
MASOX (ESONET) Expedition, Svalbard, 2011
Research vessel: Polar Star (US Coast Guard)
Research vessel: TBA
Objectives: Gas hydrate melting on the Arctic shelf
Objectives: Gas hydrate melting at the
continental margin
Coordination: R. Coffin, Narval Research Institute, USA
10 µm
Fig. 2: Methylosinus
Fig. 2:trichosporium
Methylosinus trichosporium
8.7
Alkalinity (mM)
pH
Alkalinity (mM)
Benthic Methanefilter
pH-C
ntro
o
l
SEM
Optical anal
considerable
and bacteria
(Fig. 3) contr
structures (F
methanotrp
such as dent
10 µm
8.7
1e
Coauthors: Giovanni Aloisi, Volker Liebetrau
2+ concentrati
2+
In
Alkalinity,
CaAlkalinity,
In with
accordance
with
Ca2+
Caaccordance
dissolution or
precipitation
of carbonates
dissolution
or precipitation
ofwas
carb
2+
2+
concentration
increased (Fig.
1f )
bacteria, Ca bacteria,
incre
Ca concentration
In this study
westudy
investigate
the effectthe
of aerobic
oxidizingoxidizing
bacteria bacteria
In this
we investigate
effect ofmethane
aerobic methane
on pH, alkalinity
evolutionevolution
and dissolution
of CaCO3ofin CaCO
a closed
on pH, alkalinity
and dissolution
a closed system.
3 in system.
The oxidation of methane by benthic microorgamisms largely affects the seafloor
carbonate system at marine methane seep locations. Aerobic oxidation of methane
(MOx) is observed in the top layer of methane-rich sediments and in the water
column, where specialized proteobacteria oxidize methane with oxygen and produce CO
1d
2.
Results:
The amount of CO2 during MOx can locally exceed the carbonate buffer capacity,
causing a decrease in pH (i.e., contribution to ocean acidification, Fig 5b), increase
in alkalinity (Fig5a-b) and dissolution of CaCO3 (Fig5c-d).
Future investigations will focus on:
- Microbial carbonate precipitation during AOM and sulfate reduction
- Carbonate nucleation details on the cellular level
- Impact of seafloor warming and ocean acidification on microbially
induced precipitation/ dissolution of carbonates
2+
d
Fig. 4a-e. Results of the Reactive Transport Model
Experimental Microbiology
major precipitation
or dissolution
CaCO3 occ
major precipitation
orof
dissolution
(Fig. 1d), alkalinity
increased,
indicating
dissolu
(Fig. 1d),
alkalinity
increased,
indica
comparison comparison
with the controls
(2.6controls
vs. 1.6 mM)
with the
(2.6a
and first measurement.
In the secondInphase
of
and first measurement.
the seco
at ~ 3.8 mM.at
During
phase
to 10
da
~ 3.8 the
mM.third
During
the(7
third
phas
indicating further
dissolution
CaCO3. of C
indicating
furtherof
dissolution
Coordiation: MASOX Project (ESONET)