ALBERT

Description: Highlights • Up to 33 km thick dominantly gabbroic crust beneath Walvis Ridge • Massive gabbro addition with subjacent cumulates to the COB south of Walvis Ridge. • Slow upper mantle at ~ 35 km depth beneath Etendeka Plateau • 4–6 km thick oceanic crust in the Angola Basin north of Florianopolis Transform • Velocity models suggest a dominant tectonic control on the location of magmatism. Abstract Voluminous magmatism during the South Atlantic opening has been considered as a classical example for plume related continental breakup. We present a study of the crustal structure around Walvis Ridge, near the intersection with the African margin. Two wide-angle seismic profiles were acquired. One is oriented NNW–SSE, following the continent–ocean transition and crossing Walvis Ridge. A second amphibious profile runs NW–SE from the Angola Basin into continental Namibia. At the continent–ocean boundary (COB) the mafic crust beneath Walvis Ridge is up to 33 km thick, with a pronounced high-velocity lower crustal body. Towards the south there is a smooth transition to 20–25 km thick crust underlying the COB in the Walvis Basin, with a similar velocity structure, indicating a gabbroic lower crust with associated cumulates at the base. The northern boundary of Walvis Ridge towards the Angola Basin shows a sudden change to oceanic crust only 4–6 km thick, coincident with the projection of the Florianopolis Fracture Zone, one of the most prominent tectonic features of the South Atlantic ocean basin. In the amphibious profile the COB is defined by a sharp transition from oceanic to rifted continental crust, with a magmatic overprint landward of the intersection of Walvis Ridge with the Namibian margin. The continental crust beneath the Congo Craton is 40 km thick, shoaling to 35 km further SE. The velocity models show that massive high-velocity gabbroic intrusives are restricted to a narrow zone directly underneath Walvis Ridge and the COB in the south. This distribution of rift-related magmatism is not easily reconciled with models of continental breakup following the establishment of a large, axially symmetric plume in the Earth's mantle. Rift-related lithospheric stretching and associated transform faulting play an overriding role in locating magmatism, dividing the margin in a magma-dominated southern and an essentially amagmatic northern segment.

Description: Abstract

Description: Magnetotellurics (MT) is a geophysical deep sounding tool that can help decipher the deep hydrology and geology of Antarctica, in concert with more established and already applied geophysical methods, such as seismology, gravity, and magnetics. Electrical conductivity is an important physical parameter to identify properties of rocks and, perhaps more importantly, constituents within, such as fluids or mineralisation.The unique conditions of Antarctica, which is largely covered with ice cause technical issues, particularly with the electric field recordings, as highly resistive snow and ice at surface of Antarctica hampers contact of the E-field sensors (telluric electrodes) with the ground. The project was a feasibility study to address this principal problem and to test modified MT equipment of the Geophysical Instrument Pool Potsdam (GIPP) in the vicinity of the Neumayer Station III (NMIII) on the Ekström Ice Shelfon.This data publication encompasses a detailed report in .pdf format with a description of the project, information on the experimental setup, data collection, instrumentation used, recording configuration and data quality. The folder structure and content of the data repository are described in detail in Ritter et al. (2019). Time-series data are provided in EMERALD format (Ritter et al., 2015).

Description: Other

Description: The Geophysical Instrument Pool Potsdam (GIPP) provides field instruments for (temporary) seismological studies (both controlled source and earthquake seismology) and for magnetotelluric (electromagnetic) experiments. The GIPP is operated by the GFZ German Research Centre for Geosciences. The instrument facility is open for academic use. Instrument applications are evaluated and ranked by an external steering board. See Haberland and Ritter (2016) and https://www.gfz-potsdam.de/gipp for more information.

Description: Walvis Ridge is an aseismic oceanic ridge stretching from the African continent to the Mid Atlantic Ridge, representing the trail of the Tristan da Cunha hotspot. To estimate the influence of the plume, a large-scale geophysical experiment was conducted in 2011 and the P-wave velocity models derived from seismic refraction data are presented here. A 480 km long profile consisting of 27 ocean bottom stations crosses the ridge approximately 600 km west of the coast, while another profile is located parallel to the ridge along the crest with an extension on the continent. 28 ocean bottom stations, 50 land receiver and 8 dynamite shots are distributed along the total length of 730 km. Crustal velocities beneath Walvis Ridge range between 5.5 km/s and 7.0 km/s, which are typical velocities for oceanic crust. The thickness, however, is approximately three times larger than normal: 17 km in the western part increasing to 22 km towards the continent. The continent ocean transition is characterized by 30 km thick crust with a high velocity body (HVB) in the lower crust and seismic velocities up to 7.5 km/s. The western boundary of the HVB is at a similar longitude as HVBs found more south. But different from those, the eastern boundary lies well within the continental domain, at the ~40 km thick crust of the Kaoko fold belt. Here, the variation of seismic velocities indicates that hot material intruded the continental crust during the initial rifting stage. However, beyond this relatively sharp boundary (40 km wide), the remaining continental crust seems not to be affected. The cross-profile indicates that Walvis Ridge might be broader than its topographic expression and that the northward lying seamounts are part of the ridge. A HVB can only be found at the northern flank of the ridge, but not at its base.

Description: Walvis Ridge is a prominent aseismic ridge in the South Atlantic, stretching across the whole oceanic crust from the African continent to the Mid Atlantic Ridge, representing the trail of the Tristan da Cunha hotspot. This proposed deep mantle plume emplaced the Parana flood basalts in South America and the Etendeka flood basalts on the African continent, prior and during the breakup of Gondwana. This temporal proximity indicates a causal relationship between the arriving plume head and the continental breakup. To estimate the influence of the plume, a large-scale geophysical experiment was conducted in 2011. The P-wave velocity models derived from seismic refraction data are presented here. A 480 km long profile consisting of 27 ocean bottom stations crosses the ridge approximately 600 km west of the coast, while a second profile is located ridge-parallel along its crest with an extension on the continent. 28 ocean bottom stations, 50 land receiver and 8 dynamite shots are distributed along the total length of 730 km. Crustal velocities beneath Walvis Ridge range between 5.5 km/s and 7.0 km/s, which are typical velocities for oceanic crust. The crustal thickness, however, is approximately three times larger than of normal oceanic crust: 17 km in the western part increasing to 22 km towards the continent. The continent ocean transition is characterized by 30 km thick crust with a high velocity body (HVB) in the lower crust and seismic velocities up to 7.5 km/s. The western boundary of the HVB is at a similar longitude as HVBs observed south of Walvis Ridge. But different from those, the eastern boundary lies well within the continental domain, at the 40 km thick crust of the Kaoko fold belt. Here, the variation of seismic velocities indicates that hot material intruded the continental crust during the initial rifting stage. However, beyond this relatively sharp boundary (40 km wide), the remaining continental crust seems unaffected by intrusions. The cross-profile indicates that Walvis Ridge might be broader than its topographic expression and that the northward lying seamounts are part of the ridge. A HVB can only be found at the northern flank of the ridge, but not at its base. We conclude, that the postulated arriving plume head did not modify the continental crust on a large scale, but was a rather regional anomaly.

Description: Large igneous provinces (LIP) are often found in close temporal and spatial proximity with continental breakups, supporting the model, that an arriving mantle plume produces large amounts of melt and has a massive influence on the breakup process. The South Atlantic is a classical example, with flood basalts on both adjacent continents and a paired age progressing ridge system connecting them with the current hotspot location at Tristan da Cunha. To estimate the influence of the plume on the preexisting continental crust, a large-scale geophysical experiment was conducted in 2011 at the intersection of Walvis Ridge with the African continent. We present four P-wave velocity models derived from seismic refraction data. One extends 430 km along the ridge crest and continues onshore to a total length of 730 km, while the other three crossing the ridge perpendicular: one (480 km long) far offshore in the oceanic regime, one (600 km) close to shelf break and the last one (400 km) onshore. Crustal velocities beneath Walvis Ridge range between 5.5 km/s and 7.0 km/s, which are typical velocities for oceanic crust. The crustal thickness, however, is approximately three times larger than of normal oceanic crust: 17 km in the western part increasing to 22 km towards the continent. The continent ocean transition is characterized by 30 km thick crust with a high velocity body (HVB) in the lower crust and seismic velocities up to 7.5 km/s. The western extend of the HVB is to a similar distance from shore as for HVBs observed south of Walvis Ridge. In contrast, the eastern boundary lies well within the continental domain, at the 40 km thick crust of the Kaoko fold belt. Here, the variation of seismic velocities indicates that hot material intruded the continental crust during the initial rifting stage. However, beyond this relatively sharp boundary (40 km wide), the remaining continental crust seems unaffected by intrusions and the root of the Kaoko belt is no eroded. The cross-profile indicates that Walvis Ridge might be broader than its topographic expression and that the northward lying seamounts are part of the ridge. A HVB can only be found at the northern flank of the ridge, but not at its base. We conclude, that the postulated arriving plume head did not modify the continental crust on a large scale, but was a rather regional anomaly.

Description: The Walvis Ridge perpendicular to the African coast offshore Namibia is believed to be caused by a long-lived hotspot, which started to erupt with the opening of the South Atlantic in mid Cretaceous. The ridge in combination with the large igneous provinces (Etendeka and Parana) in South America and Namibia is today considered to be a classical model for hotspot driven continental break-up. To unravel details on how the crust and mantle were modified by such a major thermal event, a large-scale geophysical on- and offshore experiment was conducted in 2011. We present p-wave velocity models of two active seismic profiles along and across Walvis Ridge. The profile along the ridge continues onshore, has a total length of ∼730 km and consists of 28 ocean bottom stations, 50 land stations and 8 dynamite shots. This section reveals a complex structure with multiple buried seamounts, strong lateral velocity gradients and indication of a high velocity body at the crust-mantle boundary beneath the shelf area. Lower crustal velocities range from 6.5 km/s in the west to 7.0 km/s in the east while the crustal thickness is approximately 28 km at the coast thinning westwards. The second profile perpendicular to the ridge is located about 140 km west of the first profile, has a length of ∼480 km and consists of 27 ocean bottom stations. The crustal thickness is well constrained by multiple Moho reflections showing a thickness of 20km under the crest of the ridge and gradually thinning to 8km towards north and south. A seamount marks the northern termination of the ridge leading to an abrupt thickening of the crust to 14km before reaching the Angola Basin. While crustal velocities of 5.5 km/s and 6.5 km/s in the upper and lower crust are similar to the first profile, lower crustal velocities north of the crest are approximately 6% higher.

Description: The season ANT-Land 2018/19 is scheduled for the period from 31 October 2017 until 28 February 2019. Most of personnel will be flown into the Antarctic and back via the air link from Cape Town within the frame of Dronning Maud Land Air Network (DROMLAN). Ship calls are scheduled for RV POLARSTERN between 5th and 7st January 2019, to supply the majority of cargo for NEUMAYER STATION III and aircraft operations. A further ship call is MARY ARCTICA between 17th and 18th January 2019. Logistics will focus on two periods of lifting of the station. Furthermore a construction team will be onsite for maintenance of the station facilities. In the vicinity of NEUMAYER STATION III geophysical, glaciological, geological, biological and atmospheric projects are planned during the summer season. Medical studies of the Berlin Centre for Space Medicine (ZWMB) and University of Munich (LMU) will be continued and extended by the station staff during the winter period. In parallel, station facilities will be used to operate the Basler BT-67 aircraft POLAR 6. The regular weather forecast service (AWI/DWD) will be provided to all aircraft operations within the Dronning Maud Land region, in particular as a contribution to DROMLAN. KOHNEN STATION will be visited by the participants of six scientific projects and maintenance work such as lifting up the station and construction work. A traverse to KOHNEN STATION including supply goods will start from NEUMAYER STATION III will start mid of November. The DALLMANN LABORATORY at Base CARLINI (Argentina) will be opened at the beginning of November 2018. It is operated in cooperation with the Instituto Antártico Argentino (IAA). During the season 2018/19 German and international scientists (one scientific group) will work at the Potter Cove and the station area.

Description: During the last season and ongoing planning, pre-site surveys are operated at the Ekströmisen, Dronning Maud Land, close to the Neumayer-Station III, with the primary target to build a stratigraphic age framework of the under-shelf-ice-sediments. These sediments are overlying the Explora Wedge [1], [2], a syn- or postrift volcanic deposit, and dipping north- to north-eastward. Expected ages could range from Late Mesozoic to Quaternary. From new vibroseismic profiles we will select sites for short core seafloor sampling of the oldest and of the youngest sediment sequences to confine their age time span. After that, we could select one or several sites for potential deep drillings (several hundred-meter-deep) with the support of international partner, if we could rise interest. The deep drillings should recover the sediments overlying the Explora Escarpment, and should discover the nature of the Explora Wedge as well. We expect that the overlying sediment sequences could reveal the history of polar amplification and climate changes in this part of Antarctica, the build-up of the East Antarctic Ice Sheet during past warmer climates and its Cenozoic and future dynamic and variability. The plan for seasons 2017/18 and 2018/19 are the testing of different sea floor sampling techniques through Hot Water Drill (HWD) holes. To select the drill sites for this shallow coring additional high resolution seismic will be acquired as well. Having holes through the shelf ice and sampling the sea floor will provide the unique opportunity for further piggy bag experiments consisting of multi-disciplinary nature. Experiments and measuring setup for oceanography, sea and shelf ice physics, geophysics, geology, hydrography, and biogeochemistry could be planned to characterize the sea-ice and shelf ice system, underlying water column, and the sediments. Video characterization underneath the shelf ice and at the seafloor, sediment trap deployment, seafloor mapping with an AUV (Leng, DFKI, ROBEX) could lead as well to innovative new interdisciplinary observations and discoveries of the sub-ice environment and ecosystem [3]. References: [1] Eisen, O., Hofstede, C., Diez, A., Kristoffersen, Y., Lambrecht, A., Mayer, C., Blenkner, R. & Hilmarsson, S., (2015), On-ice vibroseis and snowstream¬er systems for geoscientific research, Polar Science, 51-65, 9, http://dx.doi.org/10.1016/j.polar.2014.10.003. [2] Kristoffersen, Y., Hofstede, C., Diez, A., Blenkner, R., Lambrecht, A., Mayer, C. & Eisen, O., (2014), Reassembling Gondwana: A new high quality constraint from vibroseis exploration of the sub-ice shelf geology of the East Antarctic continental margin, J. Geophys. Res. Solid Earth, 9171-9182, 119 [3] Kuhn, G. & Gaedicke, C., (2015), A plan for interdisciplinary process-studies and geoscientific observations beneath the Ekström Ice Shelf (Sub-EIS-Obs), Polarforschung, 99-102, 84

Description: Drilling into marine sediments and their subsequent basement provides sound constraints on the geological history of a region. Although marine sediments have been successfully cored globally, the most valuable information about the paleo ice sheet evolution of East Antarctica is hidden in the inaccessible sub ice shelf deposits in our research area. Drilling of the presumably Cretaceous-Cenozoic sediments and the underlying basaltic basement is planned at the Ekstroem Ice Shelf. Thus, in the austral summer season 2016/17 an over-ice seismic presite survey was conducted to gain information on the sediment and basement structures. In this context, a precise depth estimate of the target horizons/basement is of critical importance for selecting the best drill sites. To achieve this, we installed seismic recording stations along several seismic reflection lines to record the refracted seismic energy at long offsets. In total, we setup 14 stations along 8 profiles. The number of stations per profile varied between 1 and 5 with a spacing of 7 to 13 km. Each station was equipped with a Reftek 130 recorder and 9 geophone chains consisting of six 4 Hz vertical components. The source was a 9-ton EnviroVibe vibrator with a maximum pressure of 57 kPa emitting a 10 s linear sweep within a frequency range of 10 to 220 Hz. The shotpoint distance was 120m. Here we present technical details and challenges of the experiment, the data processing and the first preliminary results.