Preface The expedition ARK XIX/3 with the German icebreaking RV ...

B. 5 Biological investigations at the Håkon Mosby Mud Volcano (HMMV)
B. 5.1 Geomicrobiology of sediments and bottom waters of the Håkon Mosby
Mud Volcano
Boetius, A., Beier, V., Niemann, H., Müller, I., Heinrich, F., Feseker, T.
Since January 2001 the BMBF-funded project MUMM (Mikrobieller Umsatz von
Methan in gashydrathaltigen Sedimenten) investigates the microbial methane
turnover above focussed sources of methane in the sea. Other key research areas
are Hydrate Ridge (Cascadia Margin off Oregon, USA, projects LOTUS and OMEGA,
GEOMAR), the pockmarks off Congo continental slope (University Bremen) and the
methane seeps of the north-western Black Sea (project GHOSTDABS, University
Hamburg). The Håkon Mosby Mud Volcano on the Barents Sea continental margin is
of medium depths and coldest site investigated in this project. The investigations at
HMMV in the framework of the project MUMM in cooperation between MPI, AWI,
University of Bremen, and the IFREMER aim at an analysis of the main factors
regulating the activity of the methanotrophic microorganisms and their contribution to
biogeochemical fluxes at this mud volcano. There are three main work packages
planned: 1) geomicrobiological investigations, 2) high resolution biogeochemistry with
microsensores (see B. 5.3; Witte, U.), 3) in situ measurements with benthic landers
(se B. B. 5.2; DeBeer, D. and Eickert, G.).
Microbially mediated anaerobic oxidation of methane (AOM) is the major biological
sink of methane in marine sediments. Hence, this process is crucial in maintaining a
sensitive balance of our atmosphere’s greenhouse gas content. However, a
fundamental understanding of the associated biology is still lacking, consequently
preventing a thorough biogeochemical understanding of an integral process in the
global carbon cycle. Studies employing stable isotopes, radiotracers, modelling, and
microbiological techniques have now established that methane in marine sediments is
oxidized biologically under anoxic conditions. Although no anaerobic methanotroph
has ever been isolated, biogeochemical studies have shown that the overall process
involves a transfer of electrons from methane to sulfate. Accordingly, the isotopic and
genetic signatures of the dominant microbial populations in environments enriched
with methane proved that this transfer is mediated by a microbial consortium that
includes archaea and sulfate-reducing bacteria. The current hypothesis is that AOM is
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