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Anaerobic Oxidation of Methane (AOM) in marine sediments Contribution 8, by Tina Treude & Antje...
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Anaerobic Oxidation of Methane (AOM) in marine
sedimentsContribution 8, by
Tina Treude & Antje Boetius
The History of AOM
In 1976 William Reeburgh discovered a steep decrease of methane in the anoxic zone of marine sediments. No methane reached the oxygenated sediment layers.The decrease in methane could only be caused by an anaerobic consumption of methane.
The History of AOMIn 1985 Marc Alperin and William Reeburgh supplied the evidence that methane is consumed by the oxidation with sulfate under anoxic conditions.
The History of AOM
Before that time the only known process of methane oxidation in marine sediments was the oxidation by oxygen:
CH4 + 2O2 CO2 + 2H2O methane oxygen carbon dioxide water
But since then a new process, called anaerobic oxidation of methane (AOM) was obvious, by which methane is oxidized by sulfate:
CH4 + SO42- CO3
2- + H2S + H2O
methane sulfate bicarbonate hydrogen sulfide water
The History of AOM
In 1994 Tori Hoehler et al. demonstrated by inhibition experiments that a consortium of methanogenic archaea and sulfate-reducing Bacteria (SRB) could mediate AOM in the sediment (see also next slide):
• AOM is stopped when a substrate (BES) is added to the sediment, that is inhibiting methanogenic archaea
•AOM is stopped when the sediment is sulfate-free
The History of AOM
The inhibition experiments of Tori Hoehler et al.
The History of AOM
In 2000 Antje Boetius et al. were able to demonstrate by molecular methods that the syntrophic partners of the AOM consortium occur in structured aggregates. In these aggregates, archaea are located in the center surrounded by the SRB.
archaea (stained red)
SRB (stained green)
The History of AOM
In 2001 Walter Michaelis et al. found out, that such AOM-consortia are able to build up a huge biomass above methane seeps in the anoxic part of the Black Sea. These reef-like structures are up to 1 m in diameter and 4 m high.
photos: GHOSTDABS, Jago-Team
The location of the microbial-reef in the Black Sea:
methane seeping area
Working platform and sampling equipment that were used for the investigation of the microbial-reef
above: Russian research vessel “Prof. Logachev”
right: German submersible “Jago” photos: GHOSTDABS
The macroscopic structure of the microbial reef
photos: GHOSTDABS, Jago-Team
30 cm
precipitated carbonates
microbial biomass
Laboratory experiments demonstrate that the microbial reef is fueled by AOM
by T. Treude & K. Nauhaus
Anaerobic oxidation of methane (AOM) and sulfate reduction (SR)
of microbial mat pieces
0
5
10
15
20
25
30
35
AOM SR
Ra
te (
µm
ol/
g d
w/d
)
Methane dependent sulfate reduction (SR) of microbial mat
pieces
0
10
20
30
40
50
SR withmethane
SR withoutmethane
Ra
te (
µm
ol/
g d
w/d
)
1:1 stoichiometry of AOM and SR
No SR without methane
Molecular identification reveal that a microbial consortium is responsible for AOM in the reef
by K. Knittel & A. Gieseke
30 cm
GHOSTDABS, Univ. Hamburg
cells stained blue
fluorescence in situ hybridization (FISH)
AOM consortia of different shapes
by A. Boetius, K. Knittel & A. Gieseke
AOM consortium above gas hydrates at Hydrate Ridge, Cascadia Margin.
aggregate-structure
"tissue"-structure
AOM consortium above gas seeps in the anoxic Black Sea.
Archea
SRB
Archea
SRB
scheme by K. Nauhaus
The AOM symbiosis
Gashydrates / Seeps
HydrogenAcetateFormateElectrons…………
Methanotroph Sulfate reducerCH4
Biomass
8 [H]
SO42-
SO42-
H2S
H2S
Electrons
Biomass
CO2 CO2
CO2
CH4 + SO42- + Ca2+ CaCO3
+ H2S + H2O
Long-term incubations with [14C]-methane proving microbial induced
carbonate precipitation
by T. Treude & A. Gieseke
radioactive carbon inside mat
slice: 75% biomass
25% carbonate precipitation
The colors represent the activity of 14C
inside a mat slice (high activity red, low activity blue)
AOM all around the world
location area water depth
(m)
AOM
(mmol m-2 d-1)
Kysing Fjord inner shelf 1 0.01
Kattegat outer shelf 65 0.83
Skagerrakupper continental
margin200 1.16
Cariaco Trenchlower continental
margin120 0.44
Hydrate Ridge gashydrate site 750 98.9
Iversen & Blackburn1981
Iversen & Joergensen1985
Iversen & Joergensen1985
Reeburgh1978
Treude et al.(in prep.)
Highest AOM rates are found in sediments bearing gas hydrates.
table by Boetius & Hinrichs (2000)
The impact of AOM
The major part of methane (>90%) that is produced in ocean sediments is consumed my microbes before it reaches the atmosphere.
Therefore AOM has a significant impact on climate regulation as methane is a 30 times stronger greenhouse gas compared to carbon dioxide.
picture: : www.solcomhouse.com
ReferencesAlperin, M.C., Reeburgh, W.S. (1985). Inhibition experiments on anaerobic methane oxidation. Appl. Environ. Microbiol. 50 (4), 940-945.Boetius, A., Hinrichs, K.-U. (2000). The anaerobic oxidation of methane: new insights in microbial ecology and biogeochemistry. Hanse Workshop "Ocean margin systems", Delmenhorst, Germany.Boetius, A., Ravenschlag, K., Schubert, C.J., Rickert, D., Widdel, F., Giesecke, A., Amann, R., Joergensen, B.B., Witte, U., Pfannkuche, O. (2000). A marine microbial consortium apparently mediating anaerobic oxidation of methane. Nature 407, 623-626.Hoehler, T.M., Alperin, M.J., Albert, D.B., Martens, C.S. (1994). Field and laboratory studies of methane oxidation in an anoxic marine sediments: evidence for methanogen-sulphate reducer consortium. Global Biochem. Cycles 8 (4), 451-463.Iversen, N., Blackburn, T.H. (1981). Seasonal rates of methane oxidation in anoxic marine sediments. Appl. Environ. Microbiol. 41 (6), 1295-1300.Iversen, N., Joergensen, B.B. (1985). Anaerobic methane oxidation rates at the sulphate-methane transition in marine sediments from Kattegat and Skagerrak (Denmark). Limnol. Oceanogr. 30 (5), 944-955.Michaelis, W., Seifert, R., Nauhas, K., Treude, T., Thiel, V., Blumenberg, M., Knittel, K., Gieseke, A., Peterknecht, K., Pape, T., Boetius, A., Amann, R., Joergensen, B.B., Widdel, F., Peckmann, J., Pimenov, N.V., Gulin, M.B. (2002). Microbial reefs in the Black Sea fueled by anaerobic oxidation of methane. Science 297, 1013-1015.Reeburgh, W.S. (1976). Methane consumption in Cariaco Trench waters and sediments. Earth Planet. Sci. Lett. 28, 337-344.
Acknowledgement
SO
SB
G
DA
HT
R/V Prof. Logachev
Contact
Tina Treude: Max Planck Institute for Marine Microbiology, Bremen, Germany,[email protected]
Antje Boetius: Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, [email protected]
MUMM-Project: http://www.mpi-bremen.de/deutsch/biogeo/mumm2.html