ALBERT

Description: Active fluid venting was observed for the first time along the Aleutian convergent margin during RV SONNE cruise 97. These subduction-induced cold vents were subsequently investigated in detail during cruise SO 110 in the summer of 1996 using the Canadian remotely operated vehicle, ROPOS. Active sites of dewatering were found at the youngest deformation structure adjacent to the decollement zone. High concentrations of reduced gases in the escaping fluids provide the nutritional and energy basis for the observed chemosynthetic communities in which clams and tubeworms dominate. Further evidence for fluid venting comes from the mineral precipitates of barite and carbonates.

Description: High acoustic seafloor-backscatter signals characterize hundreds of patches of methane-derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the Nile Deep Sea Fan (NDSF) in the Eastern Mediterranean Sea. During a high-resolution ship-based multibeam survey covering a ~ 225 km**2 large seafloor area in the Central Province of the NDSF we identified 163 high-backscatter patches at water depths between 1500 and 1800 m, and investigated the source, composition, turnover, flux and fate of emitted hydrocarbons. Systematic Parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies (flares), indicative of gas bubble streams, above 8% of the high-backscatter patches. In echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution. Visual inspection of three high-backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter. Volume estimates, considering results from high-resolution autonomous underwater vehicle (AUV)-based multibeam mapping, were used to calculate the amount of carbonate-bound carbon stored in these slabs. Additionally, the flux of methane bubbles emitted at one high-backscatter patch was estimated (0.23 to 2.3 × 10**6 mol a**-1) by combined AUV flare mapping with visual observations by remotely operated vehicle (ROV). Another high-backscatter patch characterized by single carbonate pieces, which were widely distributed and interspaced with sediments inhabited by thiotrophic, chemosynthetic organisms, was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption (0.1 to 1 × 10**6 mol a**-1) and dissolved methane flux (2 to 48 × 10**6 mol a**-1). Our comparison of dissolved and gaseous methane fluxes as well as methane-derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo-, bio-, and hydrosphere at cold seeps.

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: Bathymetry based on data recorded during POS498 between 18.04.2016 and 01.05.2016. The cruise aimed to recover observatories with the help of the Remotely Operated Vehicle (ROV) MARUM‐SQUID, while the second main objective of the cruise was to recover sediments to study the thermal structure as well as the temporal evolution of the mud volcanoes. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry post-processing and its products. Description of the data source: During the RV POSEIDON cruise POS498 the ELAC SB3050 multibeam echo sounder with a nominal sounding frequency of 50 kHz was utilized. 384 beams are formed for each ping while the seafloor is detected using amplitude and phase information for each beam sounding. For further information consult http://www.mdsys.co.kr/down/ELAC/SB_3050.pdf. During POS498 the swath angle was set mostly between 90 and 70° with a survey speed of 6 knots. The ELAC SB3050 worked reliable. Problems during the acquisition were during bad weather conditions and a malfunction of the integrated navigation system (F180 unit) by which the heading of the ship in the data diverged from the true heading, which resulted in misplaced beams. Responsible person for hydroacoustics during this cruise / PI: David Voelker (dvoelker@marum.de). Description of data processing: Postprocessing and products were conducted by the Seafloor-Imaging & Mapping group of MARUM/FB5, responsible person: Paul Wintersteller (seafloor-imaging@marum.de). The open source software MB-System suite (Caress, D.W., and D.N. Chayes, MB-System Version 5.5, open source software distributed from the MBARI and L-DEO web sites, 2000-2012.) was utilized for this purpose. A tide correction was applied, based on the Oregon State University (OSU) tidal prediction software (OTPS) that is retrievable through MB-System. Though CTD measurements were taken during the POS498 cruise, and these were most of the time sufficient to represent the changes in the sound velocity (SVP) throughout the study area, some SVP's had to be reanalysed. Changes in SVP were applied (mbset) while further roll, pitch and heave corrections were not necessary for the POS498 data. Bathymetric data has been manually cleaned for existing artefacts with mbeditviz. NetCDF (GMT) grids of the product and the statistics were created using mbgrid No total propagated uncertainty (TPU) has been calculated to gather vertical or horizontal accuracy. The currently published bathymetric grid of the cruise has a resolution of 70 m. A higher resolution is, at least partly, achievable. The grid extended with _num represents a raster dataset with the statistical number of beams/depths taken into account to create the depth of the cell. The extended _sd -grid contains the standard deviation for each cell. All grids produced are retrievable through the PANGAEA database (www.pangaea.de). Chief Scientist: H. Sahling (hsahling@marum.de) CR: http://oceanrep.geomar.de/33307/ CSR: http://www.bsh.de/aktdat/dod/fahrtergebnis/2016/20160082.htm A special thanks goes to the watch keeper of the hydroacoustic systems during POS498: David Volker, Markus Loher Another thanks goes to the student helper, that helped to create the product: Stefanie Gaide

Description: Multibeam echosounder (MBES) data recorded during RV POSEIDON cruise POS498 between 18.04.2016 and 01.05.2016 off the south coast of Turkey in the Anaximander Mountains. The cruise aimed to recover observatories with the help of the Remotely Operated Vehicle (ROV) MARUM‐SQUID 2000, while the second main objective of the cruise was to recover sediments to study the thermal structure as well as the temporal evolution of the mud volcanoes. 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 RV POSEIDON cruise POS498 the ELAC SB3050 multibeam echo sounder with a nominal sounding frequency of 50 kHz was utilized. 384 beams with a 1.5°(TX)/2°(RX) footprint are formed for each ping while the seafloor is detected using amplitude and phase information for each beam sounding. For further information consult http://www.mdsys.co.kr/down/ELAC/SB_3050.pdf. During POS498 the swath angle was set mostly between 90 and 70° with a survey speed of 6 knots. The ELAC SB3050 worked reliable in spite of working at the lower end of its depth range. Problems during the acquisition only occurred during bad weather conditions and a malfunction of the integrated navigation system (F180 unit) by which the heading of the ship in the data diverged from the true heading, which resulted in misplaced beams. Responsible person for hydroacoustic during this cruise / PI: David Voelker (dvoelker@marum.de). Chief Scientist: H. Sahling (hsahling@marum.de) CR: http://oceanrep.geomar.de/33307/ CSR: http://www.bsh.de/aktdat/dod/fahrtergebnis/2016/20160082.htm A special thanks goes to the watch keeper during POS498: Markus Loher