Description: Submarine mud volcanoes release sediments and gas-rich fluids at the seafloor via deeply-rooted plumbing systems that remain poorly understood. Here the functioning of Venere mud volcano, on the Calabrian accretionary prism in ~1,600 m water depth is investigated, based on multi-parameter hydroacoustic and visual seafloor data obtained using ship-borne methods, ROVs, and AUVs. Two seepage domains are recognized: mud breccia extrusion from a summit, and hydrocarbon venting from peripheral sites, hosting chemosynthetic ecosystems and authigenic carbonates indicative of long-term seepage. Pore fluids in freshly extruded mud breccia (up to 13 °C warmer than background sediments) contained methane concentrations exceeding saturation by 2.7 times and chloride concentrations up to five times lower than ambient seawater. Gas analyses indicate an underlying thermogenic hydrocarbon source with potential admixture of microbial methane during migration along ring faults to the peripheral sites. The gas and pore water analyses point to fluids sourced deep (〉3 km) below Venere mud volcano. An upward-branching plumbing system is proposed to account for co-existing mud breccia extrusion and gas seepage via multiple surface vents that influence the distribution of seafloor ecosystems. This model of mud volcanism implies that methane-rich fluids may be released during prolonged phases of moderate activity.

Description: We investigated dissolved methane distributions along a 6 km transect crossing active seep sites at 40 m water depth in the central North Sea. These investigations were done under conditions of thermal stratification in summer (July 2013) and homogenous water column in winter (January 2014). Dissolved methane accumulated below the seasonal thermocline in summer with a median concentration of 390 nM, whereas during winter, methane concentrations were typically much lower (median concentration of 22 nM). High-resolution methane analysis using an underwater mass-spectrometer confirmed our summer results and was used to document prevailing stratification over the tidal cycle. We contrast estimates of methane oxidation rates (from 0.1 to 4.0 nM day**-1) using the traditional approach scaled to methane concentrations with microbial turnover time values and suggest that the scaling to concentration may obscure the ecosystem microbial activity when comparing systems with different methane concentrations. Our measured and averaged rate constants (k') were on the order of 0.01 day**-1, equivalent to a turnover time of 100 days, even when summer stratification led to enhanced methane concentrations in the bottom water. Consistent with these observations, we could not detect known methanotrophs and pmoA genes in water samples collected during both seasons. Estimated methane fluxes indicate that horizontal transport is the dominant process dispersing the methane plume. During periods of high wind speed (winter), more methane is lost to the atmosphere than oxidized in the water. Microbial oxidation seems of minor importance throughout the year.

Description: Sponges host a remarkable diversity of microbial symbionts, however, the benefit their microbes provide is rarely understood. Here, we describe two new sponge species from deep-sea asphalt seeps and show that they live in a nutritional symbiosis with methane-oxidizing (MOX) bacteria. Metagenomics and imaging analyses revealed unusually high amounts of MOX symbionts in hosts from a group previously assumed to have low microbial abundances. These symbionts belonged to the Marine Methylotrophic Group 2 clade. They are host-specific and likely vertically transmitted, based on their presence in sponge embryos and streamlined genomes, which lacked genes typical of related free-living MOX. Moreover, genes known to play a role in host–symbiont interactions, such as those that encode eukaryote-like proteins, were abundant and expressed. Methane assimilation by the symbionts was one of the most highly expressed metabolic pathways in the sponges. Molecular and stable carbon isotope patterns of lipids confirmed that methane-derived carbon was incorporated into the hosts. Our results revealed that two species of sponges, although distantly related, independently established highly specific, nutritional symbioses with two closely related methanotrophs. This convergence in symbiont acquisition underscores the strong selective advantage for these sponges in harboring MOX bacteria in the food-limited deep sea.

Description: Between 25.10. and 18.11.2009, Multibeam data based on the KONGSBERG Simrad EM120 were acquired during RV Maria S. Merian cruise MSM13/3.The investigation of diversity and community distribution of chemosynthetic ecosystems related to fluid escape structures at the eastern and central provinces of the Nile fan (Eastern Mediterranean Sea) was the main research target. Additionally element transport rates and fluid export related to these fluid seeps was further explored. This cruise was in corporation with the DIWOOD program. Therefore wood, which was deployed in 2006/2007, was recovered to investigate the influence of wood degradation on ecosystems. To collect gas/fluid and sediment samples, the ROV QUEST4000 (MARUM) was utilized. During the cruise hydroacoustic systems (Multibeam and Parasound) were recorded to generate high-resolution maps of the research areas as well as to identify and to quantify seepage structures. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval. Description of the data source: During the MSM13-3 cruise, the hull-mounted KONGSBERG EM120 multibeam echosounder (MBES) was utilized for bathymetric mapping in water depth beyond 1000 m as it allows accurate bathymetric mapping up to full ocean depth. Two linear transducer arrays in Mills Cross configuration transmit a nominal sonar frequency of 12 kHz with an maximum beam width of 130° across track and 1° along track. 191 individual beams were created per ping. The actual footprint of a beam has a dimension of 1° by 2°. On flat bottom, the achievable swath width can reach up to six times the water depth. The angular coverage sector and beam pointing angles were set to vary automatically with depth according to achievable coverage. For further information on the system, consult https://www.km.kongsberg.com/. Responsible person during this cruise / PI: Paul Wintersteller (pwintersteller@marum.de), Heiko Sahling and Miriam Römer (mroemer@marum.de). Chief Scientist: Antje Boetius CR: https://www.tib.eu/de/suchen/download/?tx_tibsearch_search%5Bdocid%5D=awi%3Adoi~10.2312%252Fcr_msm13_3&cHash=91ccabc6630ae9bbd4b3fc995f742237#download-mark CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2009/20100012.htm

Description: For the detection of gas emissions, the water column data recorded with the MBES Kongsberg EM122 and EM710 were edited and displayed with QPS FLEDERMAUS using the 3D-Midwater tool. In order to detect and locate gas emissions emanating from the seafloor into the water column, MBES data were analyzed consistently for flares to achieve an almost complete coverage within the study area. The multibeam system allows to detect flares aside from the nadir of the ship's track as all beams of the swath are utilized. A table listing locations (latitude and longitude) and water depth (in meters) of detected flares is summerized from Meteor cruise M84/2 to the Black Sea focussing on the Crimean continental margin to the Kerch peninsula slope.

Description: Submarine mud volcanoes develop through the extrusion of methane-rich fluids and sediments onto the seafloor. The morphology of a mud volcano can record its extrusive history and processes of erosion and deformation affecting it. The study of offshore mud-volcano dynamics is limited because only few have been mapped at resolutions that reveal their detailed surface structures. More importantly, rates and volumes of extruded sediment and methane are poorly constrained. The 100 m high twin cones of Venere mud volcano are situated at ~1600 m water depth within Squillace Canyon along the Ionian Calabrian margin, Mediterranean Sea. Seafloor bathymetry, and backscatter data obtained by a ship-based system and an autonomous underwater vehicle (AUV) allow mapping of mudflow deposits of the mud volcano and bedforms in the surrounding canyon. Repeated surveying by AUV document active mud movement at the western summit in between 2014 and 2016. Through sediment coring and tephrochronology, ages of buried mudflow deposits are determined based on the sedimentation rate and the thickness of overlying hemipelagic sediments. An average extrusion rate of 27000 m^3/year over the last ~882 years is estimated. These results support a three-stage evolutionary model of Venere mud volcano since ~4000 years ago. It includes the onset of quiescence at the eastern cone (after ~2200 years ago), erosive events in Squillace Canyon (prior to ~882 years ago), and mudflows from the eastern cone (since ~882 years). This study reveals new interactions between a mud volcano and a canyon in the deep sea.

Description: In 2003, the Chapopote asphalt flow was discovered in the southern Gulf of Mexico at a depth of 2,900 m. Subsequent exploration has expanded the known extent of asphalt volcanism across abyssal depths in much of this region. Aspects of asphalt flow morphology are analogous to ropy pāhoehoe flows known from eruptions of basaltic lava on land, but the timing and formation sequence of asphalt flows has been difficult to infer because limited visibility in the deep ocean makes it challenging to image large areas of the seafloor. Combining data from autonomous underwater vehicle mapping and remotely operated vehicle navigation with powerful optical mosaicking techniques, we assembled georeferenced images of the Chapopote asphalt flows. The largest image captured an area of 3,300 m² with over 15 billion pixels and resolved objects at centimeter scale. Augmenting this optical resolution with microbathymetry led to the recognition that very large asphalt pavements exhibiting highly varied morphologies and weathering states comprised a series of at least three separate flow units, one on top of another. The Chapopote asphalt volcano likely erupts during phases of intensified activity separated by periods of reduced activity. After extrusion, chemical and physical changes in the asphalt generate increasing viscosity gradients both along the flow path and between the flow's surface and core. This allows the asphalt to form pāhoehoe lava-like shapes and to support dense chemosynthetic communities over timescales of hundreds of years.