ALBERT

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: The Rio Grande Rise in the western South Atlantic Ocean has been interpreted as either an oceanic plateau related to the Tristan-Gough mantle plume, or a fragment of detached continental crust. Here we present new major and trace element data for volcanic rocks from the western and eastern Rio Grande Rise and the adjacent Jean Charcot Seamount Chain. The eastern Rio Grande Rise and older parts of the western Rio Grande Rise are comprised of tholeiitic basalt with moderately enriched trace element compositions and likely formed above the Tristan-Gough mantle plume close to the southern Mid-Atlantic Ridge. Younger alkalic lavas from the western Rio Grande Rise and the Jean Charcot Seamount Chain were formed by lower degrees of melting beneath thicker lithosphere in an intraplate setting possibly during rifting of the plateau. There is no clear geochemical evidence that remnants of continental crust are present beneath the Rio Grande Rise.

Description: Recent studies indicate that mantle plumes, which transfer material and heat from the earth’s interior to its surface, represent multifaceted upwellings. The Tristan-Gough hotspot track (South Atlantic), which formed above a mantle plume, documents spatial geochemical zonation in two distinct sub-tracks since ~70 Ma. The origin and the sudden appearance of two distinct geochemical flavors is enigmatic, but could provide insights into the structural evolution of mantle plumes. Sr–Nd–Pb–Hf isotope data from the Late Cretaceous Rio Grande Rise and adjacent Jean Charcot Seamount Chain (South American Plate), which represent the counterpart of the older Tristan-Gough volcanic track (African Plate), extends the bilateral-zonation to ~100 Ma. Our results support recent numerical models, demonstrating that mantle plumes can split into distinct upper mantle conduits, and provide evidence that these plumelets formed at the plume head-to-plume tail transition. We attribute the plume zonation to sampling the geochemically-graded margin of the African Large Low-Shear-Velocity Province.

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: The magnetotelluric impedance tensor elements and errors were calculated with the software BIRRP (Chave &Thomson, 2004; doi:10.1111/j.1365-246X.2004.02203.x). Magnetotelluric measurements were conducted from December 2010 to January 2011 at the Walvis Ridge, offshore Namibia. Coordinates of the MT stations are included in the EDI files and cover an area at ~8°E - 12°E, ~18°S-22°S. Station deployment and recovery was conducted on the two cruises MSM17/1 and MSM17/2 on German research vessel Maria S. Merian as part of the SPP1375 priority program SAMPLE. The SAMPLE project focused on the processes linked to continental margin formation.

Description: BRAVOSEIS (Bransfield Volcano Seismology) is an interdisciplinary project exploring volcanism in the Bransfield back-arc basin, Antarctica. Partners from Spain (amongst others UGR, project leader), Germany (AWI, GFZ) and the US (CUNY, UW, WHOI) performed various geophysical onshore and offshore measurements in the Antarctic seasons 2017-2018, 2018-2019 and 2019-2020. A key element of the project was the operation of a large long-term amphibious network of broadband seismometer in the Bransfield Strait, on the adjoining South Sheltland Islands, and on the Antarctic Peninsula. Nine broadband coean-bottom seismometer (OBS) from the German Instrument Pool of Amphibian Seismology (DEPAS) were deployed as part of this network with RV Sarmiento de Gamboa in January 2019 (cruise SDG076). They were distributed along the entire basin, one station supplemented a dense array of short-period OBS around the Orca seamount. Eight instruments could be recovered in February 2020 with RV Hespérides (cruise HE0188), one OBS is still missing. All stations recorded data for the full deployment period. Unfortunately, the clock drift of all stations turned out to be non-linear, a skew measurement was possible for four stations only.

Description: The data set provides unprocessed and processed seismic reflection data collected during Expedition PS72 (ARK-XXIII/3) onboard RV Polarstern in the southeastern Arctic Ocean in 2008. Detailed data acquisition parameters for the profile are documented in the expedition report (Jokat, 2015). Metadata, recording parameters, and the seismic data processing sequence are documented in the EBCDIC-Headers enclosed in the seg-y files. Navigation information is included in the seg-y headers, and in the CDP-SHOT-latitude-longitude file (see data product). A ReadMe file additionally lists the metadata and recording parameters for the seismic profile. The data set is grouped into three categories: 1. Raw data comprise (a) navigation data with date, time, and coordinates, (b) a shot list of date, time and shot-number, and (c) demultiplexed seismic data in seg-y format. Please note: for some very short consecutive profiles the demultiplexed raw data still are merged in one file. 2. Primary data consist of (a) CDP-sorted data in seg-y format, and (b) navigational data in a conventional UKOOA- file. 3. The data product is provided as (a) stacked or time-migrated version of the seismic profile in seg-y format and (b) a list with CDP and SHOT numbers as well as geographical coordinates. Please note that the low-frequency reflector running parallel to the seafloor at a depth of about 190 ms (~150 m) does not appear to be a ghost or bubble signal. It is likely an artifact created during acquisition that was not removed.