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

- How much methane is oxidized aerobically in the bottom water ?
- What are the dominant microbial populations mediating anaerobic methane
turnover ?
- Is their isotopic signature indicative of methane consumption ?
- What is the link between microbial methane turnover and the
chemosynthetic communities at the HMMV ?
Materials and Methods
The Håkon Mosby Mud Volcano (HMMV) at about 72° N 14° E was first investigated
during an international cruise with RV "Professor Logachev" in 1996. It is the only
mud volcano in a polar region that has been studied in greater detail by photo and
video camera observation. The HMMV is situated on the continental slope north-west
of Norway at a water depth of 1250 m. It has a diameter of about 2 km, with an outer
rim populated by methane-depending, chemosynthetic communities and an inner
centre of about 500 m diameter where fresh muds are expelled. Between the central
plain and the outer rim, a complex topography of hills and depressions can be found
which is derived from the transport of young sediments. All investigations focussed at
the three main geobiological communities in the centre of HMMV, at the Beggiatoa
mats and Pogonophora fields as well as at the surrounding reference sites. In addition
small-scale gradients were sampled such as within a Beggiatoa mat (mat-covered
and not-covered sediments), and between freshly expelled mud and aged mud.
The major aim of this study was the investigation of microbial sulfate reduction (SRR)
and anaerobic methane oxidation (AOM) in methane enriched surface sediments of
the HMMV, as well as sampling the sediments for microbiological and molecular
analysis. Samples were obtained from the sediment cores which were retrieved by
the ROV pushcores, by TV guided multiple corer hauls (Tab. B5.1-1) and gravity
cores (Tab. B5.1-2). In parallel to the on board rate measurements, sub-samples
were taken from cores to determine the total number of bacteria, to quantify different
taxonomic groups of bacteria by fluorescence in situ hybridisation (FISH, 16s rDNA
clone libraries, DGGE) and to investigate the metabolic activity of methane
consuming micro-organisms involved in sulfate reduction as well as anaerobic and
aerobic methane oxidation under controlled laboratory conditions in microcosms.
Furthermore, sediment subsamples were obtained to investigate the distribution of
lipid products derived from members of AOM consortia and their stable carbon
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