Description: Sub bottom profiler (SBP) aka sediment echosounder data. Sediment echosounder measurements were conducted continuously by means of Teledyne PARASOUND DS3 (P70) parametric sediment echosounder during both R/V MARIA S. MERIAN cruises, MSM20-2 (Jegen et al., 2015) and MSM24, until the shutdown of the system due to technical reasons on cruise MSM24. The system's beam width is 4.5° along-track and 5.0° across-track. The primary high frequency signal (PHF) with a frequency of about 18 kHz was recorded for water-column investigations while the secondary low frequency signal (SLF) with a frequency of 4 kHz is used to image the shallow sub-seafloor. This selection of four PARASOUND profiles were converted into SEG-Y data by using the PS32segy tool (Hanno Keil, University of Bremen, Germany). Afterwards, the ReflexW software57 (Sandmeier, 2012) was used to low-pass filter the data and to mute the water column.

Description: 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.

Description: Content The attached raster-files are saved in the formats PDF and georeferenced PNG. The shapefile "VolcanicCones_Tristan", including its auxiliary files, as well as all other georeferenced files are shown in the projected coordinate system UTM28S with geodetic datum WGS84 (EPSG # 32728). The two Excel files contain a, the volume calculation of the volcanic cones and b, the decision table for the BPI classification. 1. Rugosity/Ruggedness raster & Benthic Terrain Modeler: To investigate the structural complexity of the study area, a rugosity (surface roughness) raster was created using the arc-chord ratio (ACR) index after Du Preez (2015). The ACR method is defined as the contoured area of the surface divided by the area of the surface orthogonally projected onto a plane of best fit. In this way, it effectively decouples rugosity from the slope. To reduce artefacts in the rugosity raster caused by the underlying bathymetry data, the ACR rugosity raster was calculated from the three-fold resampled bathymetry data. The benthic terrain of Tristan da Cunha was analyzed using ESRIs ArcGIS™ with the aid of the ArcGIS application's Benthic Terrain Modeler (BTM) v. 3.0 (Lundblad et al., 2006; Wright et al., 2012) which classifies bathymetry data and analyses seafloor characteristics. The most important derivative for this analysis is the Bathymetric Position Index (BPI). The BPI is modified from the Topographic Position Index, which is used in terrestrial environments (Weiss, 2001). It compares the elevation of each cell in the bathymetry raster with the mean elevation of a defined neighborhood around that cell. In this analysis, an annulus neighborhood with an inner and outer radius is used. To identify both fine and broad features on the seafloor, two BPI grids were created using an inner radius of 15 km and an outer radius of 22.5 km for the broad-scale BPI raster and 1.5 km and 3 km, respectively, for the fine-scale BPI raster. Since the bathymetric position tends to be auto-correlated (Erdey-Heydorn, 2008), the BPI grids were standardized. The overall structural analysis was based on a classification dictionary (Supplementary Material Table S2) which defines several geomorphological structures by their broad and fine scale BPI and their slope. The transition from flat areas to broad slopes was set to 3° and from broad to steep slopes to 25°. 2. Slope & Aspect Slope and aspect are first order derivates of the bathymetry. They are both shown in colored categories. 3. Backscatter The beam time series are shown as a mosaic in stretched greyscale from black & white and in color white to brown. For analysis the dataset was separated in categories and shown in colors from dark green to light brown. 4. Volume calculations of volcanic cones: We utilized the GIS software GlobalMapper v18.2 for volume calculations of the volcanic cones, though the prework to generate the volcanic cone polygons was conducted with ESRIs ArcGIS™. The result of the BTM classification was used to extract the four classes that represent outcrops or local ridges (see Supplementary Material Table S2: Class 6, 11, 13 and 14). This outcrop raster was then converted into polygon features. Areas smaller than 0.1 km² were excluded from further analyses. Since it is not possible to select polygons by their shape, a manual selection of the polygon features was necessary to remove all polygons that do not represent circular cone-shaped morphologies (e.g., elongated ridges or parts of the main islands). Furthermore, all polygons were buffered as the outcrop classes from the BTM classification result do not extend to the approximate base of the outcrops, which is due to the functionality of the BPI. The best buffer distance was measured exemplarily (here we buffered with 200 m). Finally, the polygons were smoothed by a Bezier Interpolation and exported as a shapefile. The actual volume calculation was conducted with GlobalMapper's analysis & measurement tool "Pile Volume" and exported as a .CSV file (Supplementary Material Table S1). Mean backscatter values were calculated for each volcanic cone by using the ArcGIS tool "Zonal Statistics". Very low (〈-68 dB) and very high (〉-8 dB) backscatter values were excluded beforehand using the "Extract by Attribute tool" as they mainly occur near the outer beams and the nadir and, therefore, most likely represent erroneous dB values.

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: Water column raw data using the ship's own Kongsberg EM 122 multibeam echosounder was not continuously recorded during RV MARIA S. MERIAN cruise MSM86. Data was recorded on 26 days between 2019-08-18 and 2019-09-13. 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. Ancillary sound velocity profiles (SVP) files from the cruise are archived at the BSH and added to the corresponding multibeam raw dataset https://doi.org/10.1594/PANGAEA.945449 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).

Description: The hydroacoustic surveys carried out during MARIA S. MERIAN cruise MSM86 were aimed at acquiring detailed information of the areas of interest (Boyd Seamount; Logi Ridge; Vesteris; Vestnesa Ridge) with respect to backscatter and bathymetry. During MARIA S. MERIAN cruise MSM86, the MBES KONGSBERG EM122 was operating almost continuously. The shallow to medium water MBES KONGSBERG EM712 system was only operating in water depths above about 1000 m. Hydroacoustic surveys were usually conducted with a vessel speed of maximum 6 kn, while for some few sub-bottom profiles, a reduced speed of about 4 kn was applied. During transits the vessel speed was increased to 8-12 kn, depending on weather conditions. Sound velocity profiles were uploaded into the recording system online. Data are unprocessed and therefore may contain incorrect depth measurements (artifacts) without further processing.

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: The hydroacoustic surveys carried out during MARIA S. MERIAN cruise MSM86 were aimed at acquiring detailed information of the areas of interest (Boyd Seamount; Logi Ridge; Vesteris; Vestnesa Ridge) with respect to backscatter and bathymetry. The shallow to medium water MBES KONGSBERG EM712 system was only operating in water depths above about 1000 m. Hydroacoustic surveys were usually conducted with a vessel speed of maximum 6 kn, while for some few sub-bottom profiles, a reduced speed of about 4 kn was applied. During transits the vessel speed was increased to 8-12 kn, depending on weather conditions. Sound velocity profiles were uploaded into the recording system online. Data are unprocessed and therefore may contain incorrect depth measurements (artifacts) without further processing.