Beschreibung: Tristan da Cunha is assumed to be the youngest subaerial expression of the Walvis Ridge hot spot. Based on new hydroacoustic data, we propose that the most recent hot spot volcanic activity occurs west of the island. We surveyed relatively young intraplate volcanic fields and scattered, probably monogenetic, submarine volcanoes with multibeam echosounders and sub-bottom profilers. Structural and zonal GIS analysis of bathymetric and backscatter results, based on habitat mapping algorithms to discriminate seafloor features, revealed numerous previously-unknown volcanic structures. South of Tristan da Cunha, we discovered two large seamounts. One of them, Isolde Seamount, is most likely the source of a 2004 submarine eruption known from a pumice stranding event and seismological analysis. An oceanic core complex, identified at the intersection of the Tristan da Cunha Transform and Fracture Zone System with the Mid-Atlantic Ridge, might indicate reduced magma supply and, therefore, weak plume-ridge interaction at present times.

Beschreibung: Highlights • Extensive asphalt deposits and asphalt volcanism at Mictlan Knoll in the southern Gulf of Mexico. • A novel type of active hydrocarbon seepage system in the southern GoM. • High-resolution seafloor mapping and seafloor manifestation of heterogeneous hydrocarbon seepage system. • Mapping, quantification and monitoring of gas emission sites in the southern GoM. • Mictlan Knoll hosts the most extensive asphalt deposits known to date in the GoM. Abstract Hydrocarbon seepage plays an essential role in defining seafloor morphology and increasing habitat heterogeneity in the deep sea whereby asphalt volcanism ranks among the most complex and proliferous hydrocarbon discharge systems that have been described to date. In this study, seepage of hydrocarbon gas and oil as well as asphalt deposits were investigated at Mictlan Knoll in the southern Gulf of Mexico. A multi-disciplinary approach was used including hydroacoustic surveys and visual seafloor observations to study the seafloor manifestations of hydrocarbon seepage. Mictlan Knoll is an asphalt volcano characterized by a crater-like depression surrounded by an elevated rim. Asphalt deposits are widespread in the depression where a large area of extensive asphalt deposits correlates with a high backscatter area (~75,000 m2). Numerous asphalt deposits appear relatively fresh and probably extruded recently, as oil bubbles were seen to emanate locally within areas covered by extensive asphalt deposits. An area of more irregular seafloor morphology occurring in the northern part of the depression is interpreted to be related to the active extrusion of asphalt below or within older surficial deposits. Additionally, 25 hydroacoustic anomalies indicative for gas bubble emissions were detected. Gas volume quantifications conducted during seafloor inspections with a remotely-operated vehicle (ROV) at a single gas escape site situated above a gas hydrate outcrop revealed up to 0.1 × 106 mol CH4/yr. Gas emission at this site, monitored by an autonomous scanning sonar device, indicated a highly variable bubble release activity. Based on our findings, it is proposed that Mictlan Knoll hosts the most extensive asphalt deposits known to date in the Gulf of Mexico.

Beschreibung: The continental slopes of the Black Sea show abundant manifestations of gas seepage in water depth of 〈720 m, but underlying controls are still not fully understood. Here, we investigate gas seepage along the Bulgarian and Romanian Black Sea margin using acoustic multibeam water column, bathymetry, backscatter, and sub-bottom profiler data to determine linkages between sub-seafloor structures, seafloor gas seeps, and gas discharge into the water column. More than 10,000 seepage sites over an area of ∼3,000 km 2 were identified. The maximum water depth of gas seepage is controlled by the onset of the structure I gas hydrate stability zone in ∼720 m depth. However, gas seepage is not randomly distributed elsewhere. We classify three factors controlling on gas seepage locations into depositional, erosional, and tectonic factors. Depositional factors are associated with regionally occurring sediment waves forming focusing effects and mass-transport deposits (MTDs) with limited sediment drape. Elongated seafloor depressions linked to faulting and gas seepage develop at the base between adjacent sediment waves. The elongated depressions become progressively wider and deeper toward shallow water depths and culminate in some locations into clusters of pockmarks. MTDs cover larger regions and level out paleo-topography. Their surface morphology results in fault-like deformation patterns of the sediment drape on top of the MTDs that is locally utilized for gas migration. Erosional factors are seen along channels and canyons as well as slope failures, where gas discharge occurs along head-scarps and ridges. Sediment that was removed by slope failures cover larger regions down-slope. Those regions are devoid of gas seepage either by forming impermeable barriers to gas migration or by removal of the formerly gas-rich sediments. Deep-rooted tectonic control on gas migration is seen in the eastern study region with wide-spread normal faulting promoting gas migration. Overall, gas seepage is widespread along the margin. Gas migration appears more vigorous in shallow waters below ∼160 m water depth, but the number of flare sites is not necessarily an indicator of the total volume of gas released.

Beschreibung: The Southern Ocean surrounding Antarctica is a region that is key to a range of climatic and oceanographic processes with worldwide effects, and is characterised by high biological productivity and biodiversity. Since 2013, the International Bathymetric Chart of the Southern Ocean (IBCSO) has represented the most comprehensive compilation of bathymetry for the Southern Ocean south of 60°S. Recently, the IBCSO Project has combined its efforts with the Nippon Foundation – GEBCO Seabed 2030 Project supporting the goal of mapping the world’s oceans by 2030. New datasets initiated a second version of IBCSO (IBCSO v2). This version extends to 50°S (covering approximately 2.4 times the area of seafloor of the previous version) including the gateways of the Antarctic Circumpolar Current and the Antarctic circumpolar frontal systems. Due to increased (multibeam) data coverage, IBCSO v2 significantly improves the overall representation of the Southern Ocean seafloor and resolves many submarine landforms in more detail. This makes IBCSO v2 the most authoritative seafloor map of the area south of 50°S.

Beschreibung: Swath sonar bathymetry data used for that dataset was recorded during RV METEOR cruise M79/2 using Kongsberg EM 120 multibeam echosounder. The cruise took place between 26.08.2009 and 21.09.2009 in the northeastern Atlantic. The main objectives of the cruise were the analysis of the structure, dynamic and natural hazard potential of the Atlantic section of the European-African plate boundary in the area of the eastern Azores (São Miguel region) and Gloria Fault. The measurements included marine geophysical experiments like refraction and reflection seismics, potential field recordings (gravity & magnetics), parametric sediment subbottom profiling and multibeam bathymetry [DOI:10.2312/cr_m79_2]. 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 M79/2 cruise, the hull-mounted KONGSBERG EM120 multibeam ecosounder (MBES) was utilized to perform bathymetric mapping in middle to deep water depths. Two linear transducer arrays in a Mills Cross configuration transmit acoustic signals of a nominal sonar frequency of 12 kHz. With 191 beams, the emission cone has a dimension of max. 140° across track and 1° along track. With a reception obtained from 288 beams, the actual beam footprint is 1° by 2°. Depending on the roughness of the seafloor, the swath width on a flat bottom is generally maximum six times the water depth. For further information on the system, consult https://www.km.kongsberg.com/. Responsible person during this cruise / PI: Luis Batista. 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 (Caress, D. W., and D. N. Chayes, MB-System: Mapping the Seafloor, https://www.mbari.org/products/research-software/mb-system, 2017) was utilized for this purpose. . SVPs taken during this cruise were not sufficient enough to correct the recorded bathymetric data. Therefor sound velocity profiles were modelled using reference profiles from the world ocean atlas (S. Levitus, 1982), extracted and calculated through the MB-System program mblevitus by utilizing the DelGrosso equation. The surface sound speed has then been adapted according to the recordings during this cruise while there were no further corrections for roll, pitch and heave applied during postprocessing. A tide correction was applied, based on the Oregon State University (OSU) tidal prediction software (OTPS) that is retrievable through MB-System. CTD measurements during the cruise were sufficient to represent the changes in the sound velocity throughout the study area. Using Mbeditviz, artefacts were cleaned manually. NetCDF (GMT) grids of the edited data as well as statistics were created with mbgrid. The published bathymetric EM120 grid of the cruise M79/2 has a resolution of 35 m. No total propagated uncertainty (TPU) has been calculated to gather vertical or horizontal accuracy. 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. The DTMs projections are given in Geographic coordinate system Lat/Lon; Geodetic Datum: WGS84. All grids produced are retrievable through the PANGAEA database (www.pangaea.de). Chief Scientist: Christian Hübscher christian.huebscher@uni-hamburg.de CR: https://www.tib.eu/de/suchen/id/awi%3Adoi~10.2312%252Fcr_m79_2/ CSR: https://epic.awi.de/id/eprint/37063/31/m79-expeditionsheft.pdf

Beschreibung: Bathymetry data was acquired during R/V METEOR cruise M84/4 at the Galician Shelf off Northwest Spain in the Northeast Atlantic between 01.05.2011 and 28.05.2011. The main objectives of the cruise were the investigation of sediment transport processes from shallow to deep waters, understanding sediment dynamics, analysis of material downslope processes and the reconstruction of modern and past environmental conditions. The cruise comprised seismic, sedimentological, magnetic, geochemical and palaeoceanographic methods. Extensive bathymetric mapping during M84/4 based on the multibeam echosounders (MBES) KONGSBERG EM710 and EM122 provided the basis for sediment coring and additional investigations. Hydroacoustic data revealed the diverse morphology in the study area, driven by both sedimentary and tectonic processes, including contouritic deposits, slope gullies, canyon/channel systems, ridges and seamounts. The sub-bottom profiler PARASOUND, multichannel seismics, ADCP, several coring devices and the electromagnetic profiler MARUM-NERIDIS III complemented the research programme of the cruise. 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 M84/4 cruise, the hull-mounted KONGSBERG EM710 multibeam echosounder (MBES) was utilized to perform bathymetric mapping of high resolution in water depths of 3 m to – theoretically – 2000 m. Best quality data is, however, achieved in water depths of less than 600 m, and in rough weather conditions less than 400 m. The EM710 operates at sonar frequencies of 70 to 100 kHz. Three to five sectors divide the transmit fan, where distinct frequencies or waveforms are transmitted sequentially. The swath width can reach 5.5 times the water depth. 256 beams with an acoustical 1°(TX)/1°(RX) footprint are formed for each ping. The transmit fan is electronically stabilized for roll, pitch and yaw. Combining phase and amplitude bottom detection algorithms allows achieving best possible accuracy. For further information, consult: https://epic.awi.de/id/eprint/26726/1/Kon2007b.pdf. The position and depth of the water column is estimated for each beam by using the detected two-way-travel time and the beam angle known for each beam, ray-traced through the water column, utilizing a proper sound speed profile. During the M84/4 cruise, the EM710 was running in a 24-hour watch mode, in addition to the EM122 and the PARASOUND sub-bottom profiling system. Acquisition of EM710 data was reliable during the whole cruise; however, problems occurred during rough weather conditions, since the EM710 lost the bottom signal in depths of more than 400 m. Responsible person during this cruise / PI: Tilmann Schwenk (tschwenk@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 (Caress, D. W., and D. N. Chayes, MB-System: Mapping the Seafloor, https://www.mbari.org/products/research-software/mb-system, 2017) was utilized for this purpose. Tide corrections and a sound velocity profile were applied to the M84/4 data; there were no corrections for roll, pitch and heave. A tide correction was applied, based on the Oregon State University (OSU) tidal prediction software (OTPS) that is retrievable through MB-System. CTD measurements during the cruise were sufficient to represent the changes in the sound velocity throughout the study area. Using Mbeditviz, artefacts were cleaned manually. NetCDF (GMT) grids of the edited data as well as statistics were created with mbgrid. The published bathymetric EM710 grid of the cruise M84/4 has a resolution of 35 m. No total propagated uncertainty (TPU) has been calculated to gather vertical or horizontal accuracy. 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. The DTMs projections are given in Geographic coordinate system Lat/Lon; Geodetic Datum: WGS84. All grids produced are retrievable through the PANGAEA database (www.pangaea.de). Chief Scientist: Till J. J. Hanebuth (thanebuth@coastal.edu) CR: https://www.tib.eu/de/suchen/id/awi%3Adoi~10.2312%252Fcr_m84_4/ CSR: https://www.ldf.uni-hamburg.de/meteor/wochenberichte/wochenberichte-meteor/m84/m84-4-scr.pdf

Beschreibung: Swath sonar bathymetry data used for that dataset was recorded during RV SONNE cruise SO175 using Kongsberg EM 120 multibeam echosounder. The cruise took place between 12.11.2003 and 30.12.2003 in the Gulf of Cadiz. The expedition aimed at a better understanding of the interaction between dynamic processes in a seismically active region with slow plate convergence. Bathymetric mapping with the multibeam echosounder (MBES) SIMRAD EM120 was utilized to image the nature of the Gibraltar Arc thrust wedge, a proposed subduction zone, and to identify possible sampling sites. 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 SO175 cruise, hull-mounted KONGSBERG EM120 multibeam ecosounder (MBES) was utilized to perform bathymetric mapping in middle to deep water depths. Two linear transducer arrays in a Mills Cross configuration transmit acoustic signals of a nominal sonar frequency of 12 kHz. With 191 beams, the emission cone has a dimension of max 140° across track and 1° along track, while the actual beam footprint is 2° by 2°. Depending on the roughness of the seafloor, the swath width on a flat bottom is maximum six times the water depth. For further information on the system, consult https://www.km.kongsberg.com/. During the cruise, an opening angle of 135 - 140° was used depending on the state of the sea, though restricting the coverage of the swath to gain a more continuous spacing of beams on the ocean floor. The spacing within these limits was controlled automatically by the echosounder system. To convert the recorded travel times into water depth, several sound velocity profiles were obtained with the shipboard CTD, providing a correction for ray bending for each beam. Responsible person during this cruise / PI: Achim Kopf (akopf@marum.de) & Ingo Grevenmeyer (igrevemeyer@geomar.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 (Caress, D. W., and D. N. Chayes, MB-System: Mapping the Seafloor, https://www.mbari.org/products/research-software/mb-system, 2017) was utilized for this purpose.SVPs taken during this cruise were not sufficient enough to correct the recorded bathymetric data. Therefore sound velocity profiles were modelled using reference profiles from the world ocean atlas (S. Levitus, 1982), extracted and calculated through the MB-System program mblevitus by utilizing the DelGrosso equation. The surface sound speed has then been adapted according to the recordings during this cruise while there were no further corrections for roll, pitch and heave applied during postprocessing. A tide correction was applied, based on the Oregon State University (OSU) tidal prediction software (OTPS) that is retrievable through MB-System. CTD measurements during the cruise were sufficient to represent the changes in the sound velocity throughout the study area. Using Mbeditviz, artefacts were cleaned manually. NetCDF (GMT) grids of the edited data as well as statistics were created with mbgrid. The published bathymetric EM120 grid of the cruise SO175 has a resolution of 35 m. No total propagated uncertainty (TPU) has been calculated to gather vertical or horizontal accuracy. 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. The DTMs projections are given in Geographic coordinate system Lat/Lon; Geodetic Datum: WGS84. All grids produced are retrievable through the PANGAEA database (www.pangaea.de). Chief Scientist: Achim Kopf (akopf@marum.de) CR: https://elib.suub.uni-bremen.de/ip/docs/ELibD1195_228.pdf CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2003/20050152.htm

Beschreibung: Our knowledge of venting at intraplate seamounts is limited. Almost nothing is known about past hydrothermal activity at seamounts, because indicators are soon blanketed by sediment. This study provides evidence for temporary hydrothermal circulation at Henry Seamount, a re-activated Cretaceous volcano near El Hierro island, close to the current locus of the Canary Island hotspot. In the summit area at around 3000-3200 m water depth, we found areas with dense coverage by shell fragments from vesicomyid clams, a few living chemosymbiotic bivalves, and evidence for sites of weak fluid venting. Our observations suggest pulses of hydrothermal activity since some thousands or tens of thousands years, which is now waning. We also recovered glassy heterolithologic tephra and dispersed basaltic rock fragments from the summit area. Their freshness suggests eruption during the Pleistocene to Holocene, implying minor rejuvenated volcanism at Henry Seamount probably related to the nearby Canary hotspot. Heat flow values determined on the surrounding seafloor (49 ± 7 mW/m2) are close to the expected background for conductively cooled 155 Ma old crust; the proximity to the hotspot did not result in elevated basal heat flow. A weak increase in heat flow towards the southwestern seamount flank likely reflects recent local fluid circulation. We propose that hydrothermal circulation at Henry Seamount was, and still is, driven by heat pulses from weak rejuvenated volcanic activity. Our results suggest that even single eruptions at submarine intraplate volcanoes may give rise to ephemeral hydrothermal systems and generate potentially habitable environments.