Description: 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.

Description: 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.

Description: Processed multibeam echosounder (MBES) data recorded during RV MARIA S. MERIAN cruise MSM20-2 between 17.01.2012 and 15.02.2012 around Tristan da Cunha. The Tristan da Cunha hotspot is thought to have played a major role in the rifting of the South Atlantic margins and the creation of the aseismic Walvis Ridge by impinging at the base of the continental lithosphere shortly before or during the breakup of the South Atlantic margins. MSM20-2 staged therefore a multi-disciplinary geophysical study of the Tristan da Cunha hotspot by acquiring passive marine electromagnetic and seismic data, bathymetric data as well as gravity data from which we will derive an electrical resistivity, velocity and density model down to a depth of several hundred kilometers. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry data post-processing, data ingest and approval. The bathymetric post-processing and creation of products were conducted by Janina Kammann (University Hamburg), Anne Strack (University Bremen / MARUM) and the Seafloor-Imaging & Mapping group of University Bremen / 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: Mapping the Seafloor, https://www.mbari.org/products/research-software/mb-system, 2017.) 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 cruise, and these were sufficient to represent the changes in the sound velocity throughout the study area. Further roll, pitch and heave corrections were not applied for the MSM20-2 data. Bathymetric data has been manually cleaned for existing artefacts with mbeditviz. With mbmosaic one creates tables of the average amplitude and/or sidescan values as a function of the grazing angle with the seafloor that can be used by the program mbprocess to correct the sidescan or amplitude data for the variation with grazing angle. The mbprocess program applies changes to an extended raw data file annotaded with a "p" like "rawfilename"p.mbXX where XX stands for the MBES type, in case of EM120 it is mb57. The processed files allow further post-processing e.g. raytracing regarding sound velocity correction, gridding on different scales and merging of data on a hydroacoustic level, and are therefor the most valuable and sustainable product of a hydrographers workflow with MB-System. Description of the data source and the raw data itself can be found under: https://doi.org/10.1594/PANGAEA.898376 A composite grid (DTM) of the bathymetry of cruises MSM20-2 and MSM24 is published with the following DOI: https://doi.org/10.1594/PANGAEA.898303 Chief scientist: Marion Jegen-Kulcsar (mjegen@geomar.de) CR: https://doi.org/10.2312/cr_msm20_2 CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2012/20120063.htm ADCP: https://doi.org/10.1594/PANGAEA.823159

Description: Processed multibeam echosounder (MBES) data recorded during RV MARIA S. MERIAN cruise MSM24 between 27.12.2012 and 21.01.2013 around Tristan da Cunha. The cruise MSM24 aimed to answer the question whether Tristan da Cunha classifies as a hot-spot with deep reaching asthenospheric anomalies and initiated the opening of the South Atlantic or whether Tristan da Cunha is a consequence of tectonic processes associated with more shallow anomalies. Another goal was to retrieve 26 ocean-bottom magnetotelluric stations (OBEM) and 22 broadband ocean-bottom seismometers (BBOBS) as well as two seismic and one magnetotelluric (MT) land stations from the uninhabited Nightingale Island. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval. The bathymetric post-processing was mainly conducted during RV MARIA S. MERIAN cruises MSM24 in 2013 around Tristan da Cunha. Final post-processing and creation of products were conducted by Janina Kammann (University Hamburg), Anne Strack (University Bremen / MARUM) and the Seafloor-Imaging & Mapping group of University Bremen / 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: Mapping the Seafloor, https://www.mbari.org/products/research-software/mb-system, 2017) 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 cruise, and these were sufficient to represent the changes in sound velocity throughout the study area. Further roll, pitch and heave corrections were not applied for the MSM20-2 and MSM24 data. Bathymetric data has been manually cleaned for existing artefacts with mbeditviz. With mbmosaic one creates tables of the average amplitude and/or sidescan values as a function of the grazing angle with the seafloor that can be used by the program mbprocess to correct the sidescan or amplitude data for the variation with grazing angle. The mbprocess program applies changes to an extended raw data file annotaded with a "p" like "rawfilename"p.mbXX where XX stands for the MBES type, in case of EM122 it is mb59. The processed files allow further post-processing e.g. raytracing regarding sound velocity correction, gridding on different scales and merging of data on a hydroacoustic level, and are therefor the most valuable and sustainable product of a hydrographers workflow with MB-System. Description of the data source and the raw data itself can be found under: https://doi.org/10.1594/PANGAEA.898378 A composite grid (DTM) of the bathymetry of cruises MSM20-2 and MSM24 is published with the following DOI: https://doi.org/10.1594/PANGAEA.898303 Chief Scientist: Wolfram H. Geissler CR: https://doi.org/10.2312/cr_msm24 CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2012/20130046.htm ADCP: https://doi.org/10.1594/PANGAEA.823160

Description: Multibeam bathymetry raw data using the ship's own Kongsberg (Simrad) EM 120 multibeam echosounder was almost continuously recorded during RV METEOR cruise M70/1. Data were recorded on 23 days between 2006-09-24 and 2006-10-17. Data cover various areas in the Mediterranean Sea. The approximate average depth of the entire dataset is around 1900m. During data acquisition the Kongsberg EM 710 multibeam echosounder was occasionally running simultaneously during the survey. The data are archived at the Federal Maritime and Hydrographic Agency of Germany (Bundesamt für Seeschifffahrt und Hydrographie, BSH) and provided to PANGAEA database for data curation and publication. No ancillary sound velocity profiles (SVP) from the cruise are archived at the BSH, thus added to this dataset. However, data analysis of the raw data reveled that SVP has been changed on several occasions during the cruise. This publication is conducted within the efforts of the German Marine Research Alliance in the core area "Data management and Digitalization" (Deutsche Allianz Meeresforschung, DAM). Data are unprocessed and therefore may contain incorrect depth measurements (artifacts) without further processing. Data can be processed e.g. with the open source software package MB-System (Caress, D. W., and D. N. Chayes, MB-System: Mapping the Seafloor, http://www.mbari.org/products/research-software/mb-system/, 2021).

Description: A digital database for glacial landforms and sediments formed in the Arctic during and since the Last Glacial Maximum (LGM) was created in order to facilitate and underpin new research on palaeo-ice sheets and tidewater glacier dynamics. The database is in geographic information system (GIS) format and is available for web download. It documents evidence of previous glacial activity as visible on the contemporary seafloor of fjords and continental shelves around all of Svalbard, Greenland, Alaska, and northern Russia, as well as north of 66°30' N in Canada and Norway. Extensive literature research was conducted to create the database, compiling a total of nearly 60,000 individual submarine landforms, more than 1,000 sediment cores, and around 230 radiocarbon dates. Glacial landforms included in the database are cross-shelf troughs, trough-mouth fans, grounding-zone wedges, overridden moraines, (mega-scale) glacial lineations, drumlins, crag-and-tails, medial moraines, terminal moraines, debris-flow lobes (including glacier-contact fans), recessional moraines, De Geer moraines, crevasse-fill ridges, eskers, hill-hole pairs, crescentic scours, and submarine channels. They were digitised as points, lines, and polygons alongside a list of their individual characteristics. Sediment core locations are attributed with a description of the sampled lithofacies and sedimentation rates where available. In an effort to make the sedimentological evidence as consistent as possible, the sedimentary record has been standardised according to a predefined nomenclature and classified into one of eight lithofacies groups commonly observed in Arctic glacimarine settings. Radiocarbon dates from the marine realm were included when thought to be relevant for constraining the timing of large-scale palaeo-ice dynamics. Outlines of bathymetric datasets, which have been used for glacial geomorphological mapping were also included, to give an overview of previously investigated research areas. The database will aid researchers in the reconstruction of LGM and Holocene ice dynamics and in the interpretation of Arctic glacial landform-sediment assemblages. Moreover, as well as providing a comprehensive bibliography on Arctic glacial geomorphological and sedimentological research, it is intended to serve as a basis for future modelling of Arctic glacier and ice sheet dynamics.

Description: Processed multibeam echosounder (MBES) data recorded during RV MARIA S. MERIAN cruise MSM24 between 27.12.2012 and 21.01.2013 around Tristan da Cunha. The cruise MSM24 aimed to answer the question whether Tristan da Cunha classifies as a hot-spot with deep reaching asthenospheric anomalies and initiated the opening of the South Atlantic or whether Tristan da Cunha is a consequence of tectonic processes associated with more shallow anomalies. Another goal was to retrieve 26 ocean-bottom magnetotelluric stations (OBEM) and 22 broadband ocean-bottom seismometers (BBOBS) as well as two seismic and one magnetotelluric (MT) land stations from the uninhabited Nightingale Island. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval. The bathymetric post-processing was conducted during during RV MARIA S. MERIAN cruises MSM24 in 2013 around Tristan da Cunha. Postprocessing and creation of products were conducted by Janina Kammann (University Hamburg), Anne Strack (University Bremen / MARUM) and the Seafloor-Imaging & Mapping group of University Bremen / 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, 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 cruise, and these were sufficient to represent the changes in the sound velocity throughout the study area. Further roll, pitch and heave corrections were not applied for the MSM20-2 and MSM24 data. Bathymetric data has been manually cleaned for existing artefacts with mbeditviz. With mbmosaic one creates tables of the average amplitude and/or sidescan values as a function of the grazing angle with the seafloor that can be used by the program mbprocess to correct the sidescan or amplitude data for the variation with grazing angle. The mbprocess program applies changes to an extended raw data file annotaded with a "p" like "rawfilename"p.mbXX where XX stands for the MBES type, in case of EM122 it is mb59. The processed files allow further post-processing e.g. raytracing regarding sound velocity correction, gridding on different scales and merging of data on a hydroacoustic level, and are therefor the most valuable and sustainable product of a hydrographers workflow. Description of the data source and the raw data itself can be found under: https://doi.org/10.1594/PANGAEA.898378 A composite grid (DTM) of the bathymetry of cruises MSM20-2 and MSM24 is published with the following DOI: https://doi.org/10.1594/PANGAEA.898303 Chief Scientist: Wolfram H. Geissler CR: https://doi.org/10.2312/cr_msm24 CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2012/20130046.htm ADCP: https://doi.org/10.1594/PANGAEA.823160

Description: Multibeam bathymetry raw data using the ship's own Kongsberg EM 710 multibeam echosounder was almost continuously recorded during RV METEOR cruise M70/1. Data were recorded on 18 days between 2006-09-23 and 2006-10-15. Data cover various areas in the Mediterranean Sea. The approximate average depth of the entire dataset is around 640m. During data acquisition the Kongsberg (Simrad) EM 120 multibeam echosounder was occasionally running simultaneously during the survey. The data are archived at the Federal Maritime and Hydrographic Agency of Germany (Bundesamt für Seeschifffahrt und Hydrographie, BSH) and provided to PANGAEA database for data curation and publication. No ancillary sound velocity profiles (SVP) from the cruise are archived at the BSH, thus added to this dataset. However, data analysis of the raw data reveled that SVP has been changed on several occasions during the cruise. This publication is conducted within the efforts of the German Marine Research Alliance in the core area "Data management and Digitalization" (Deutsche Allianz Meeresforschung, DAM). Data are unprocessed and therefore may contain incorrect depth measurements (artifacts) without further processing. Data can be processed e.g. with the open source software package MB-System (Caress, D. W., and D. N. Chayes, MB-System: Mapping the Seafloor, http://www.mbari.org/products/research-software/mb-system/, 2021).