Description: We mapped, sampled, and quantified gas emissions at the continental margin west of Svalbard during R/V Heincke cruise He-387 in late summer 2012. Hydroacoustic mapping revealed that gas emissions were not limited to a zone just above 396 m below sea level (m b.s.l.). Flares from this depth gained significant attention in the scientific community in recent years because they may be caused by bottom water-warming induced hydrate dissolution in the course of global warming and/or by recurring seasonal hydrate formation and decay. We found that gas emissions occurred widespread between about 80 and 415 m b.s.l. which indicates that hydrate dissolution might only be one of several triggers for active hydrocarbon seepage in that area. Gas emissions were remarkably intensive at the main ridge of the forlandet moraine complex in 80 to 90 m water depths, and may be related to thawing permafrost. Focused seafloor investigations were performed with the remotely operated vehicle (ROV) "Cherokee". Geochemical analyses of gas bubbles sampled at about 240 m b.s.l. as well as at the 396 m gas emission sites revealed that the vent gas is primarily composed of methane (〉 99.70%) of microbial origin (average d13C = -55.7 per mil V-PDB). Estimates of the regional gas bubble flux from the seafloor to the water column in the area of possible hydrate decomposition were achieved by combining flare mapping using multibeam and single beam echosounder data, bubble stream mapping using a ROV-mounted horizontally-looking sonar, and quantification of individual bubble streams using ROV imagery and bubble counting. We estimated that about 53 × 10**6 mol methane were annually emitted at the two areas and allow a large range of uncertainty due to our method (9 to 118 × 10**6 mol yr**-1). These amounts, first, show that gas emissions at the continental margin west of Svalbard were in the same order of magnitude as bubble emissions at other geological settings, and second, may be used to calibrate models predicting hydrate dissolution at present and in the future, third, may serve as baseline (year 2012) estimate of the bubble flux that will potentially increase in future due to ever-increasing global-warming induced bottom water-warming and hydrate dissolution.

Description: Five georeferenced seafloor photomosaics from three different cold seep sites in the periphery of Venere mud volcano, Ionian Sea (Central Mediterranean). The photographs for each mosaic were acquired using the remotely operated vehicle (ROV) MARUM QUEST 4000m during RV METEOR cruise M112 (2014). Photos were taken from altitudes 1-5 m above seafloor using a Prosilica GT6600C camera vertically mounted on the ROV. The photomosaics were compiled with the LAPM tool (Marcon et al. 2013) and geo-referenced by using the smoothed ultra-short baseline (USBL; IXSEA Posidonia 6k) navigation data of the ROV. Seafloor positioning by USBL has an accuracy better than 10 m, or 0.05-0.2% of the slant range. Photomosaics have been rectified manually in Global Mapper® software based on obvious seafloor structures and are provided in GeoTIFF format (WGS84 coordinate system).

Description: We present differential bathymetry and sediment core data from the Japan Trench, sampled after the 2011 Tohoku-Oki (offshore Japan) earthquake to document that prominent bathymetric and structural changes along the trench axis relate to a large (~27.7 km**2) slump in the trench. Transient geochemical signals in the slump deposit and analysis of diffusive re-equilibration of disturbed SO4**2- profiles over time constrain the triggering of the slump to the 2011 earthquake. We propose a causal link between earthquake slip to the trench and rotational slumping above a subducting horst structure. We conclude that the earthquake-triggered slump is a leading agent for accretion of trench sediments into the forearc and hypothesize that forward growth of the prism and seaward advance of the deformation front by more than 2 km can occur, episodically, during a single-event, large mega-thrust earthquake.

Description: Gridded bathymetry based on acquisition recorded during M112 between 06.11.2014 and 15.12.2014 in the eastern Mediterranean Sea. The aim of the cruise was to investigate in mud volcanoes of the Calabrian Arc in Italian waters, where 54 potential mud volcanoes have been documented while it remained unclear whether they are still active or not. Therefore, the bathymetric surveys were accompanied with investigations in the water column. Several sound velocity profiles (SVPs) were taken to correct the bathymetry. 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 cruise M112 the Kongsberg EM122 multibeam echosounder with a nominal sounding frequency of 12 kHz was utilized. 288 beams (and up to 864 soundings in equidistant and dual swath mode) are formed for each ping with a 1°(Tx)/2°(Rx) footprint while the seafloor is detected using amplitude and phase information for each beam sounding. For further information consult https://www.km.kongsberg.com/. The EM122 was recording constantly within the permitted areas, either designated to bathymetry surveys or flare imaging-surveys. Responsible person during this cruise / PI: Paul Wintersteller (pwintersteller@marum.de) and Christian Ferreira (cferreira@marum.de). Description of data processing: Postprocessing and products were conducted by the Seafloor-Imaging & Mapping group of MARUM, 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. CTD measurements were taken during the M112 cruise and these were sufficient to represent the changes in the sound velocity (SVP) throughout the study area. Further roll, pitch and heave corrections were not applied for the M112 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. For scientific purposes a higher resolution is at least partly, achievable and is used. 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: G. Bohrmann gbohrmann@marum.de CSR: http://www.bsh.de/aktdat/dod/fahrtergebnis/2014/20140278.htm A special thanks goes to the watch keeper of the hydroacoustic systems during M112: M. Wiebe, D. Praeg, C. Johansen,O. Candoni, T. Biller, W. Menapace Another thanks goes to the student helpers, that helped to create the product: T. Biller, N. Brueckner

Description: Hydroacoustic raw data recorded during M112 between 06.11.2014 and 15.12.2014 in the eastern Mediterranean Sea. The aim of the cruise was to investigate in mud volcanoes of the Calabrian Arc in Italian waters, where 54 potential mud volcanoes have been documented while it remained unclear whether they are still active or not. Therefore, the bathymetric surveys were accompanied with investigations in the water column. Several sound velocity profiles (SVPs) were taken to correct the bathymetry. 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 cruise M112 the Kongsberg EM122 multibeam echosounder with a nominal sounding frequency of 12 kHz was utilized. 288 beams (and up to 864 soundings in equidistant and dual swath mode) are formed for each ping with a 1°(Tx)/2°(Rx) footprint while the seafloor is detected using amplitude and phase information for each beam sounding. For further information consult https://www.km.kongsberg.com/. The EM122 was recording constantly within the permitted areas, either designated to bathymetry surveys or flare imaging-surveys. Responsible person during this cruise / PI: Paul Wintersteller (pwintersteller@marum.de) and Christian Ferreira (cferreira@marum.de). Chief Scientist: G. Bohrmann gbohrmann@marum.de CSR: http://www.bsh.de/aktdat/dod/fahrtergebnis/2014/20140278.htm A special thanks goes to the watch keeper during M112: M. Wiebe, D. Praeg, C. Johansen,O. Candoni, T. Biller, W. Menapace