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: Herein, we publish the simulated global annual mean temperature (THO), salinity (SAO), ice compactness (SICOMO), Atlantic Meridional Overturning Circulation (AMOC), Global Meridional Overturning Circulation (GMOC), zonal velocity (UKO), meridional velocity (VKE), 10m u-velocity (u10), 10m v-velocity (v10), mixed layer depth (zmld), horizontal barotropic streamfunction (PSIUWE) and sealevel (ZO) over a time period of 100 years retrieved from equilibrium climate simulations for the Miocene (~23-15 Ma) and use different Greenland-Scotland Ridge (GSR) and Fram Strait (FS) sill depths as a representative for different tectonic settings that occur during the subsidence interval and utilized in the publication by Hossain et al. (2020). The climate data has been produced with COSMOS (ECHAM5/JSBACH/MPIOM/OASIS3), utilized at a resolution of T31 in the atmosphere (19 hybrid sigma-pressure levels) and a resolution of GR30 (bipolar orthogonal curvilinear grid, formal resolution of ~3.0°x1.8°) in the ocean (40 z-coordinate levels). The model setup refers to boundary conditions (incl. changes in orography, bathymetry, physical land surface characteristics, ice sheets, atmospheric CO2) representative for the Miocene. Details on setup and identifiers of Miocene model simulations can be found in Table 1 and Supplementary Table 1 of Hossain et al., 2020.

Description: Ice thickness from radar data over eastern Dronning Maud Land, with geographical coordinates and dates of acquisition in 2013, 2014, and 2015. Airborne acquisition was completed with aircraft POLAR 6 as part of the GEA collaborative project between the Federal Institute for Geosciences and Natural Resources and Alfred Wegener Institute.

Description: This data set contains airborne gravity data across central Dronning Maud Land, East Antarctica, acquired during the austral summer of 2009/2010 and within the project 'West-East Gondwana Amalgamation and its Separation' (WEGAS). The data span the offshore Astrid Ridge, and parts of the Nivl and Lazarev ice shelves. The survey was conducted using a ZLS Ultrasys Lacoste & Romberg Air/Sea gravimeter S56 installed into - and operated with - the research aircraft Polar 5. Base readings were performed with a handheld gravity meter at the base station Novolazarevskaja and in Cape Town. A ground speed of 130 knots and a time-domain filter of 220 s leads to a spatial resolution of around 7 km. The average crossover error after bias adjustment is 4.2 mGal. When citing this data set, please also cite the associated manuscript: Eisermann, H., Eagles, G. & Jokat, W. Coastal bathymetry in central Dronning Maud Land controls ice shelf stability. Sci Rep 14, 1367 (2024). https://doi.org/10.1038/s41598-024-51882-2.

Description: The lack of consistent and reliable estimates of the bathymetry beneath the ice shelves of western Dronning Maud Land is addressed by inverting airborne gravity data to model the underlying bathymetry. The gravity inversion is supported by known depth reference points from seismic data, multibeam and ice thickness radar data across grounded ice sheets. The dataset comprises seabed and ice base depths of Ekström, Atka, Jelbart, Fimbul and Vigrid ice shelves relative to WGS84.

Description: The lack of consistent and reliable estimates of the bathymetry beneath the Roi Baudouin and Borchgrevink ice shelves of Dronning Maud Land is addressed by inverting airborne gravity data to model the underlying bathymetry. The bathymetric model presented here is mainly based on geophysical data sets acquired over the course of three consecutive seasons in early 2011, early 2012 and late 2012 using the Alfred Wegener Institute's Basler BT-67 aircraft 'Polar 5' and 'Polar 6' within the research program 'Geodynamic Evolution of East Antarctica' (GEA I – GEA III). The gravity inversion is supported by known depth reference points from multibeam data close to calving fronts and ice thickness radar data across grounded ice sheets. See source data sets. The dataset comprises seabed and ice base depths relative to WGS84 at a reolution of 5 km.

Description: According to classic plume theory, the Tristan da Cunha mantle plume played a major role in the rifting of the South Atlantic margins by impinging at the base of the continental lithosphere shortly before or during the breakup of the South Atlantic. Onshore the Tristan mantle plume is associated with the emplacement of the Parana-Etendeka flood basalt province ~132 Ma, and offshore with the age-progressive Walvis Ridge and associated young seamount province. The global data is lacking coverage and therefore resolution around the Tristan da Cunha for shallower mantle depths. The search for deep-reaching geophysical/thermal anomalies beneath Tristan da Cunha was the starting point for a multi-disciplinary geophysical experiment to acquire passive marine electromagnetic, seismic and bathymetric data within the framework of the SPP-1375 “South Atlantic Margin Processes and Links with onshore Evolution” (SAMPLE) funded by the German Science foundation. The experiment included two expeditions with the German research vessel MARIA S. MERIAN in 2012 and 2013. Between February 2012 and January 2013, a network of 24 ocean bottom seismometers (OBS) from the German DEPAS pool (Deutscher Geräte-Pool für Amphibische Seismologie) and 26 ocean-bottom magneto-telluric stations from GEOMAR Kiel and the University of Tokyo were deployed around the archipelago of Tristan da Cunha. The seismological stations are equipped with a Güralp CMG-40T wideband seismometer (60 s) incorporated in a titanium pressure housing, a hydrophone, and a GEOLON MCS (Marine Compact Seismocorder) data logger from SEND GmbH Hamburg, Germany. Each sensor channel is sampled at 50 Hz (2 OBS at 100 Hz), preamplifier gain of the hydrophone channel is 4 and 1 for the three seismometer components. The seismometers are connected to a cardanic levelling mechanism, which was activated every 21 days to level the sensors. Based on previous experiments and triangulation of some stations, the accuracy of the positions is estimated to 500 m. To complement the ocean-bottom network and the existing observatory on Tristan da Cunha (TRIS), two land seismometers and one magnetotelluric station were installed on Nightingale Island located southwest of the main island each of which was equipped with a Güralp-3ESP seismometer (60 s) and an EarthData data logger. As recording parameters, we chose 100 Hz sampling rate and low preamplifier gain (0.4). One of the stations (NIG01) recorded earthquake data for the entire year, while the second station failed after few days due to water damage. Unfortunately, the permanent station TRIS failed also during the experiment.

Description: A set of multichannel seismic reflection lines across the southeastern Lomonosov Ridge and adjacent basins was collected in 2014 during RV Polarstern cruise ARK XXVIII/3 (PS87). The data provide constraints on the coupled evolution of ocean circulations, deposition regime and regional tectonic processes. The survey set-up for most lines comprised a streamer of 3000 m length (240 channels), and a 24-liter G-gun array. Shots were fired every 15 s resulting into a shot point spacing of 35-40 m. Data were recorded for 12 s at a sample rate of 1 ms. The seismic data processing comprised sorting in a CDP interval of 25 m (= max. fold 145), and velocity analysis (every 100 CDP = 2.5 km). Interval velocities for the seismic units are adopted from the stacking velocities. After the removal of noisy traces and spherical divergence correction the traces were stacked and migrated with a finite-difference time-migration. For a successful suppression of sea floor multiple an f-k filter was applied. In general, the data were filtered with a band pass of 10 - 90 Hz, and an automatic gain control with a gate length of 1000 ms was applied. The dominant frequency of the seismic signals is about 35 Hz, which enables a maximum vertical resolution of about 11-18 m across the sedimentary units. A marked low-frequency reflector with reversed polarity parallels the sea floor at shallow water depths of 190 ms TWT (150 m). The signal turned out to be an arctefact, and in some parts the amplitude strength was succesfully attenuated by a designature filter. The presented data-set provides migrated seismic reflection seismic lines in segy-format.

Description: Herein, we publish the simulated global annual mean surface air temperature (SAT), sea surface temperature (SST), sea surface salinity (SSS), sea ice cover (seaice), surface albedo (albedo) and total cloud cover (aclcov) over a time period of 100 years retrieved from equilibrium climate simulations for the Middle Miocene and Preindustrial. We simulate Miocene and Preindustrial climate states at different atmospheric CO2 concentrations. The model data has been used in the publication by Hossain et al., 2022. The climate data has been produced with AWI Earth System Model (AWI-ESM2.1; ECHAM6/JSBACH/MPIOM2/ OASIS3‐MCT), utilized at a spectral resolution of T63 (~1.88° x 1.88°) in the atmosphere with 47 vertical layers. FESOM2 uses the COREII mesh. The Miocene model setup is based on the combined high-resolution (0.1° x 0.1°) global bathymetry and topography (Middle Miocene; ~14 Ma) of Paxman et al. (2019), Hochmuth et al. (2020) and Straume et al. (2020). The model setup refers to boundary conditions (incl. changes in orography, bathymetry, physical land surface characteristics, ice sheets, atmospheric CO2) representative for the Miocene and Preindustrial. Details on setup and identifiers of Miocene and Preindustrial model simulations can be found in Table 1 of Hossain et al., 2022.