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The HAyenkon Mosby mud volcano is a 1.5-km-diameter geological structure located on the Southwest Barents Sea slope at a water depth of 1,270 m. High-definition seabed mapping of the mud volcano has been carried out in 2003 and 2006. A comparative analysis of the bathymetry and backscatter maps produced from the two surveys shows subtle morphological changes over the entire crater of the mud volcano, interpreted to be the consequence of mud eruption events. Mud temperature measurements point to a persistently warm mud at shallow depth in the crater. This is explained by upward fluid advection, rather than conductive cooling of mud flows. The small-scale spatial variability in the temperature distribution may be related to mud outflows or changes in the fluid flow regime. Furthermore, the locations of free gas venting observed in 2006 were found to differ from those of 2003. Our observations of overall similar topographic profiles across the mud volcano in 2003 and 2006 suggest that eruption events would have been modest. Nevertheless, the data bring evidence of significant change in activity even over short time intervals of only 3 years. This may be a characteristic shared by other submarine mud volcanoes, notably those considered to be in a quiescent stage.

Submarine hydrocarbon seeps are geologically driven “hotspots” of increased biological activity on the seabed. As part of the HERMES project, several sites of natural hydrocarbon seepage in the European seas were investigated in detail, including mud volcanoes and pockmarks, in study areas extending from the Nordic margin, to the Gulf of Cádiz, to the Mediterranean and Black seas. High-resolution seabed maps and the main properties of key seep sites are presented here. Individual seeps show ecosystem zonation related to the strength of the methane flux and distinct biogeochemical processes in surface sediments. A feature common to many seeps is the formation of authigenic carbonate constructions. These constructions exhibit various morphologies ranging from large pavements and fragmented slabs to chimneys and mushroom-shaped mounds, and they form hard substrates colonized by fixed fauna. Gas hydrate dissociation could contribute to sustain seep chemosynthetic communities over several thousand years following large gas-release events.

Isis mud volcano is located on the upper slope of the Nile deep-sea fan and has been described as the surface expression of a deep-seated gas chimney [Loncke, L., Gaullier, V., Mascle, J., Vendeville, B., 2002. Shallow structure of the Nile deep-sea fan: interactions between structural heritage and salt tectonics; consequences on sedimentary dispersal. In: CIESM (Ed.), Turbidite systems and deep-sea fans of the Mediterranean and the Black seas. CIESM Workshop Series. vol. 17. Monaco]. Detailed geothermal and geochemical investigations of Isis MV have been carried out during the NAUTINIL (2003) and MIMES (2004) cruises within the framework of the Euro-margins/Mediflux project. Sediment temperatures of more than 40 °C at 10 m below the seafloor at the center of the mud volcano indicate an exceptionally high level of activity. Rapidly decreasing temperature gradients away from the center support the hypothesis of a dominantly axisymmetric functioning of Isis MV. The microbathymetry along dive tracks of the submersible Nautile reveals the presence of terraces and shows that the temperature gradients at shallow sediment depth follow the morphology. At the center, porewater profiles are characterized by a rapid decrease of chlorinity within the uppermost meter of the sediments, whereas the chlorinity of cores taken at short distances away is equal to bottom water values. Applying simple analytical models to the data provides evidence of recent mud volcano activity but no straightforward explanation of the observed anomalies, which points to a transient regime of variable fluid flow, possibly accompanied by episodic mud eruptions. Numerical modeling suggests that rapid cooling of the sediment column and downward progression of the sharp decrease in porewater chlorinity observed between the two cruises is related to episodic infiltration of bottom seawater into the mud.

Marine mud volcanoes are significant source locations contributing to the marine methane cycle. Enhanced heat flow, unique chemoautotrophic communities, occurrence of massive gas hydrates and large gas plumes are direct evidences of elevated methane concentrations and the dynamic environment of mud volcanoes. Related to the high concentrations and large inventories of CH4 in surface sediments only a fraction of the methane is exported to the bottom water. This is mainly due to chemoautotrophic communities oxidizing methane and proving a microbial filter reducing CH4 fluxes. Although these processes were studied for several mud volcanoes still little is known about the spatial pattern and the areas covered by chemoautotrophic communities or by present mud flows.For this purposes the Håkon Mosby Mud Volcano (HMMV), which is located at the continental slope of the Barents Sea, was studied by several dives with the Remotely Operated Vehicle Victor6000. During these dives a high resolution microbathymetric map, with a footprint of 25 x 25 cm and a vertical resolution of better than 10 cm was derived. Furthermore, video streams of the bottom camera was converted into georeferenced mosaics, providing a detailed image about the spatial distribution of seafloor features as bacterial mats, pogonophorans, both indicating methane oxidation, or mud flows. Based on visual inspection of 2310 georeferenced mosaics covering an area of 46160 m², different biogeochemical habitats were identified and quantified on a m²-basis and stored within a geodatabase. By application of GIS based and geostatistical techniques as indicator kriging the distribution of different biogeochemical habitats were quantified and mapped for the entire HMMV.Considering the flat and hummocky area of HMMV, approximately 16% of the flat centre is nearly void of any benthic communities. This area is considered as a region of high methane discharge into bottom water. An area of 5% located in the south-eastern part

Håkon Mosby mud volcano is located on the SW Barents Sea slope at a water depth of approximately 1250 m. In-situ temperature measurements using gravity corers equipped with autonomous temperature loggers and a short temperature lance operated by an ROV were collected during three cruises between 2003 and 2006, revealing an exceptionally high level of activity and a complex thermal structure of the mud volcano. Simple analytical models were applied to the measured data to estimate rates of specific discharge and to test the hypothesis of episodic mud eruptions. Strongly curved profiles from 4 to 16 m below the seafloor suggest fluid flow at rates from 1 m/year close to the limits of the central area to more than 4 m/year approaching the geometrical center. At the limits of the central area, the profiles show distinct maxima at sediment depths of about 10 to 15 m, which are interpreted as the result of lateral flow. Repeated measurements at shallow depths along a transect crossing the central area revealed a persistent pattern of temperature gradients, while changes in the absolute values point to temporal variability. Temperatures gradients of more than 40 °C/m within the upper half meter of the sediments close to the geometrical center suggest even higher rates of specific discharge than estimated from the deeper profiles. These high rates of fluid flow are most likely accompanied by frequent mud eruptions of small volume and limited local extent.

High-resolution seismic experiments, employing arrays of closely spaced, four-component ocean-bottom seismic recorders, were conducted at a site off western Svalbard and a site on the northern margin of the Storegga slide, off Norway to investigate how well seismic data can be used to determine the concentration of methane hydrate beneath the seabed. Data from P-waves and from S-waves generated by P–S conversion on reflection were inverted for P- and S-wave velocity (Vp and Vs), using 3D travel-time tomography, 2D ray-tracing inversion and 1D waveform inversion. At the NW Svalbard site, positive Vp anomalies above a sea-bottom-simulating reflector (BSR) indicate the presence of gas hydrate. A zone containing free gas up to 150-m thick, lying immediately beneath the BSR, is indicated by a large reduction in Vp without significant reduction in Vs. At the Storegga site, the lateral and vertical variation in Vp and Vs and the variation in amplitude and polarity of reflectors indicate a heterogeneous distribution of hydrate that is related to a stratigraphically mediated distribution of free gas beneath the BSR. Derivation of hydrate content from Vp and Vs was evaluated, using different models for how hydrate affects the seismic properties of the sediment host and different approaches for estimating the background-velocity of the sediment host. The error in the average Vp of an interval of 20-m thickness is about 2.5%, at 95% confidence, and yields a resolution of hydrate concentration of about 3%, if hydrate forms a connected framework, or about 7%, if it is both pore-filling and framework-forming. At NW Svalbard, in a zone about 90-m thick above the BSR, a Biot-theory-based method predicts hydrate concentrations of up to 11% of pore space, and an effective-medium-based method predicts concentrations of up to 6%, if hydrate forms a connected framework, or 12%, if hydrate is both pore-filling and framework-forming. At Storegga, hydrate concentrations of up to 10% or 20%

Marine mud volcanoes are significant source locations contributing to the marine methane cycle. Enhanced heat flow, unique chemoautotrophic communities, occurrence of massive gas hydrates and large gas plumes are direct evidences of elevated methane concentrations and the dynamic environment of mud volcanoes. Related to the high concentrations and large inventories of CH4 in surface sediments only a fraction of the methane is exported to the bottom water. This is mainly due to chemoautotrophiccommunities oxidizing methane and proving a microbial filter reducing CH4 fluxes. Although these processes were studied for several mud volcanoes still little is known about the spatial pattern and the areas covered by chemoautotrophic communities or by present mud flows.For this purposes the Håkon Mosby Mud Volcano (HMMV), which is located at the continental slope of the Barents Sea, was studied by several dives with the Remotely Operated Vehicle Victor6000. During these dives a high resolution microbathymetric map, with a footprint of 25×25 cm and a vertical resolution of better than 10 cm was derived. Furthermore, video streams of the bottom camera were converted into georeferenced mosaics, providing a detailed image about the spatial distribution of seafloor features as bacterial mats, pogonophorans, both indicating methane oxidation, or mud flows. Based on visual inspection of 2310 georeferenced mosaics covering an area of 46,160 m2, different biogeochemical habitats were identified and quantified on a m2-basis. By application of geostatistic techniques as indicator kriging the distribution of different biogeochemical habitats was quantified and mapped for the entire HMMV.Considering the flat and hummocky area of HMMV, approximately 16% (115,165 m2) of the flat centre is nearly void of any benthic communities. This area is considered as a region of high methane discharge into bottom water. An area of 5% (38,244 m2), located in the south-eastern part, is densely inhabited b

Mud volcanism is an important natural source of the greenhouse gas methane to the hydrosphere and atmosphere1, 2. Recent investigations show that the number of active submarine mud volcanoes might be much higher than anticipated (for example, see refs 35), and that gas emitted from deep-sea seeps might reach the upper mixed ocean6, 7, 8. Unfortunately, global methane emission from active submarine mud volcanoes cannot be quantified because their number and gas release are unknown9. It is also unclear how efficiently methane-oxidizing microorganisms remove methane. Here we investigate the methane-emitting Haakon Mosby Mud Volcano (HMMV, Barents Sea, 72° N, 14° 44' E; 1,250 m water depth) to provide quantitative estimates of the in situ composition, distribution and activity of methanotrophs in relation to gas emission. The HMMV hosts three key communities: aerobic methanotrophic bacteria (Methylococcales), anaerobic methanotrophic archaea (ANME-2) thriving below siboglinid tubeworms, and a previously undescribed clade of archaea (ANME-3) associated with bacterial mats. We found that the upward flow of sulphate- and oxygen-free mud volcano fluids restricts the availability of these electron acceptors for methane oxidation, and hence the habitat range of methanotrophs. This mechanism limits the capacity of the microbial methane filter at active marine mud volcanoes to <40% of the total flux

In high latitudes, currently the only well-known mud volcano is the Haakon Mosby Mud Volcano (HMMV) witch was discovered in 1995 and is located in the deep sea at the continental slope of the western Barents Sea fan. Its sediments are rich in CH4 and molecular and geochemical techniques have been used to detect the presence of anaerobic oxidation of methane (AOM). Specifically adapted to mud-volcano environments as sulphur-oxidizing bacteria (dominant genus Beggiatoa) and tube worms(Pogonophora) which rely on endosymbiotic bacteria have been recorded from this site. They benefit from the product sulphide and settle at the sediment/water interface.The activity of these various microbial communities thus act as an effective biological filter for methane seepage at mud volcanoes as HMMV: high methane concentrations in surface sediments are found in areas of uncovered mud, whereas CH4 is considerably lower in regions covered by mats of Beggiatoa or dense population ofPogonophora. The spatial analysis and quantification of the areas using Pogonophora, Beggiatoa and uncovered mud as "indicators for methane release" and their relation to temperature data and topography for HMMV is objective of this study.During several dives by the remotely operated vehicle (ROV) Victor6000 a microbathymetric map was generated and more than 2300 geo-referenced video mosaics, covering an area of 46160m2 along a transect of more than 17km length, were analyzed with application of a habitat indicator classification within a GÍS. Considering the area of HMMV of ca. 1.2x1.2km the data allows spatial extrapolations by Indicator Kriging. This provides an estimate about the distribution of benthic habitats for the entire mud volcano. Divided into the indicator classification the examined surface, the area of the video mosaics, is covered to 47.1% by Pogonophora, to 5% by Beggiatoa and to 47.9% by mud. After the interpolation the entire mud volcano is covered to 34.3% by Pogonophora, to 4.8% by Beg