lipid biomarkers trace methane consumption by microbial communities in sediments from the marmara...
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N. Chevalier1, I. Bouloubassi1, D. Birgel2, M.H Taphanel1
1 LOCEAN, UMR 7159, CNRS/Université P. et M. Curie, Paris, France2 University of Vienna, Department of Geodynamics and Sedimentology, Vienna, Austria
LIPID BIOMARKERS TRACE METHANE CONSUMPTION BY
MICROBIAL COMMUNITIES IN SEDIMENTS FROM THE
MARMARA SEA
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Mazurenko et al., 2003
Places where fluids (enriched in methane) are seeping out of the ocean floordue to the geology of the underlying sediments and/or due to the physiologicalfunctionning of the subsurface microbial community
COLD SEEPS
Widely distributed on ocean margins
Reservoirs of huge amounts ofmethane often in the form of hydrates
2
SPECIFIC INTEREST FOR THE STUDY OF METHANE SEEPAGES
- Biology
Methane fuels peculiar forms of life ! Deep biosphere
- Economy
Methane is an appealing energy resource !
- Climate
Methane is a potent greenhouse gas !
Potential destabilisation of methane hydrates (through global warming ?) may release huge CH4 quantities (positive feedback!).This may have happened in the past ?
3
• More than 90% of the methane produced/emitted in marine sediments is removed before it enters the hydrosphere and atmosphere
-> There is a methane barrier !
Microbial methane oxidation – key process
FACTS
4
Two ways of microbial CH4 consumption
Process discovered in the 2000’sMajor regulator of methane fluxesSo far not cultivated archaeaPrecise metabolism?Other microbes as well?
Aerobic by methanotrophic bacteria at the sediment-water interface or in the water column
ΔG°= -204 kJ mol-1
CH4 + 2O2CO2 + 2H2O
Anaerobic by methanotrophic archaea and sulfate-reducing bacteria in deeper zones of the sediment
ΔG°= ~-17 kJ mol-1
CH4 + SO42-HCO3
- + HS- + H2O
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Cold seeps associated with the North Anatolian Fault zone in the Sea of Marmara
MARNAUT CRUISE – Nautile submersible
6
Reduced sediments, polychaetes, microbial mats
MARNAUT CRUISE – Nautile submersible : Field evidence
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Origin of methane
• Thermogenic above leaky anticlines– Thrace basin source
• Dominantly biogenic in Cinarcik basin
Bourry et al., 200911
Chevalier, Bouloubassi . Geobiology (submitted)
165916601661
MARMARA SEA SEDIMENTS
We applied molecular and isotopic toolsto unravel microbial processes related with methane cycling
Push Cores
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Distinctive ‘taxonomic’ structural features > > community structure
Concentrations > > relative abundances of microbial groups
> > biomass of extant (active) organisms
Stable carbon isotopes > > carbon source utilized, carbon flow
O
OX
OH
X’OH
O
O X
Molecular – Isotopic Tools : lipid biomarkers
Constituents of microbial cell membranes
Which microbes are there ? What are they doing ?
13
Core 1659 PC4 (S. Cinarcik Basin) – Archaeal lipids
AOM
δ13C, per mil
-140 -120 -100 -80 -60 -40 -20
De
pth
(cm
)
µg/g
0
2
4
6
8
10
12
14
16
0 5 10 15
Archaeol
sn-2-OHAr
ΣPMIs
Archaeal lipids highly depleted in 13C
Chevalier, Bouloubassi . Geobiology (submitted)
-> Anaerobic Oxidation of Methane (AOM) by ANME archaea
-> archaea assimilate methane-derived Carbon
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AOM/SR
Core 1659 PC4 (S. Cinarcik Basin) – Bacterial lipids D
ep
th(c
m)
δ13C, per milµg/g
-140 -120 -100 -80 -60 -40 -20
0
2
4
6
8
10
12
14
16
0 5 10 15
cyC17:0ω5,6
C16:1ω5
Me-C16
Highly 13C-depleted bacterial (sulphate reducers-SRB) lipids
CH4 + SO42- > HS- + HCO3
- + H2O
Chevalier, Bouloubassi . Geobiology (submitted)
-> SRB assimilate (at least partially) methane-derived carbon
-> AOM coupled to SR
SMTZ
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AOM-related microbial communities show specific lipid biomarker patterns
e.g., sn2-hydroxyarchaeaol/archaeol, isotopic offsets vs. CH4, C16:1w5 FA/ i-C15:0
FA, relative abundance of cyC17:0w5,6 FA, 10Me-C16:0 FA
Diagnostic biomarker indices can thus trace specific AOM-microbes
Identity of ANME Archaea and SR bacteria
Confirmation by 16S rRNA gene analyses
In core 1659 PC4 : dominant ANME-2 archaeaDesulfosarcina/Desulfococcus (DSS) SRB
16
Chevalier, Bouloubassi . Geobiology (submitted)
1659
AOM
CH4 escapes ? – high flow ?Deeper SMTZ? – low flow ? √
MARMARA SEA SEDIMENTS
1660
AOM
1661
AOM
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CH4 + SO42- > HS- + HCO3
- + H2OAOM - SR
These authigenic carbonates sequester methane-derived carbon !
They are paleo-archives of previously active phases of seepage !
Fuels chemosynthetic fauna > typical cold seep benthic ecosystems
May trigger precipitation of diagenetic carbonates (through an increase in alkalinity of pore waters)
Ca2+, Mg2+, Fe2+ + HCO3- > ( Ca,Mg,Fe) CO3 + H+
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Chevalier, Bouloubassi , Marine Geology, 2011
Authigeniccarbonates do precipitatedthrough microbialAOM
Dominant AOM assemblages consistof ANME-2 archaeaand associated DSS - SRB
MARMARA SEA CARBONATES
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Table 2
1659R1 1661R5 1664R2 1667R3
µg/g dw 13C (‰) µg/g dw 13
C (‰) µg/g dw 13C (‰) µg/g dw 13
C (‰)
Archaeol 8.7 −108 27.9 −107 14.5 −92 22.2 −111
Sn-2-hydroxyarchaeol 23.5 −113 85.8 −109 50.4 −95 58.1 −108
Extented-hydroxyarchaeol a
0.2 nd 0.4 nd 2.6 −92 2.4 nd
Crocetane nd nd 8.1 −103 3.2 −69 4.1 −109
Crocetene nd nd 1.0 −101 0.4 nd 0.6 −103
PMI:1b
nd nd − − − − 0.3 nd
PMI:2 nd nd 1.1 −88 3.4 −88 2.9 −108
PMI:3 nd nd 0.3 nd 2.1 −92 3.4 −111
PMI:4 nd nd 0.6 nd 1.8 −75 1.3 −100
PMI:5 nd nd − − − − 0.2 nd
3-O -phytanyl-glycerolether 0.5 −105 1.7 −110 1.2 −92 0.5 nd
−: not detected; nd: not determined.
a Stadnitskaia et al. (2008)
Concentrations and stable carbon isotopic composition (in ‰ V-PDB) of archaeal lipids extracted from carbonate
samples associated to cold seeps in the Marmara Sea.
In samples 1659R1 and 1664R2, an unresolved complex mixture (UCM) appeared in the hydrocarbon fraction as a hump
area between about n -C16 and n -C32. In sample 1659R1, the quantification of hydrocarbons was not possible because
of the too high amount of the UCM.
b Unsaturated pentamethylicosenes and the numeral refers to the number of double bonds
Table 3
1659R1 1661R5 1664R2 1667R3
µg/g dw 13C (‰) µg/g dw 13
C (‰) µg/g dw 13C (‰) µg/g dw 13
C (‰)
fatty acids
C14:0 FA 9.1 −78 5.4 −30 1.9 −48 19.8 −89
i -C15:0 FA 6.4 −90 6.0 −91 5.3 −80 8.0 −100
ai -C15:0 FA 3.5 nd 2.3 nd 2.4 −74 4.9 −95
C16:1ω5 FA 10.5 −85 1.1 nd 2.6 −68 7.7 −90
C16:0 FA 10.2 −58 17.6 −30 4.9 −36 8.0 −74
10Me-C16:0 FA 2.6 nd 3.5 nd 1.8 −82 9.7 −97
CyC17:0ω5,6 FA 22.8 −91 3.6 nd 1.5 −76 13.7 −89
monoalkyl glycerol ethers
C14:0 MAGE 0.9 −90 0.7 nd nd nd nd nd
C16:1 MAGE 3.1 −86 − − nd nd 0.6 nd
C16:0 MAGE 1.8 −90 nd nd 0.7 nd 0.3 nd
Me-C16:0 MAGE 0.9 −88 0.7 nd 0.6 nd 1.3 nd
CyC17:0 MAGE 1.5 −87 − − − − nd nd
−: not detected; nd: not determined.
Concentrations and stable carbon isotopic composition (in ‰ V-PDB) of fatty acids (FAs) and non-isoprenoid
monoalkyl glycerol ethers (MAGEs) extracted from carbonate samples associated to cold seeps in the Marmara Sea and
related to bacterial lipids from microbial sources.
Microbial biomass trapped within the mineral lattice
ARCHAEAL LIPIDS
BACTERIAL LIPIDS
In newly explored fluid emission zones in the Sea of Marmara :
13C-depleted archaeal and bacterial biomarkers evidence active
AOM coupled to SR within the upper 20 cm of sediments (S. ÇinarcikBasin)
Molecular evidence for AOM/SR is absent at sites from the N.Çinarcik Basin and the Central Basin, but pore water profiles suggest itlikely occurs in deeper sections
Diagnostic biomarker fingerprints point to ANME-2 archaea andsulphate-reducing bacteria from the Desulfosarcina/Desulfococcusclusters as predominant members of the AOM consortia
AOM is responsible for authigenic carbonate precipitation
SUMMARY
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Molecular isotopic approaches are powerfull tools to unravel:
- methane consumption processes- microbial communities involved
Molecular isotopic approaches are powerfull proxies to detect:
- Present day and past events of methane seepage
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