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,ttreude@mpi-bremen.de

Antje Boetius: Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, aboetius@awi-bremerhaven.de

MUMM-Project: http://www.mpi-bremen.de/deutsch/biogeo/mumm2.html