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  • 1
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    Preserved landscapes underneath the Antarctic Ice Sheet reveal the geomorphological history of Jutulstraumen Basin (2021)
    Wiley
    Details
    Publication Date: 2021-08-28
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
    Published by Wiley on behalf of British Society for Geomorphology.
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  • 2
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    Seismicity in the vicinity of the Tristan da Cunha hotspot: Particular plate tectonics and mantle plume presence (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 122 (12). pp. 10427-10439.
    Details
    Publication Date: 2020-02-06
    Description: Earthquake locations along the southern Mid-Atlantic Ridge have large uncertainties due to the sparse distribution of permanent seismological stations in and around the South Atlantic Ocean. Most of the earthquakes are associated with plate tectonic processes related to the formation of new oceanic lithosphere, as they are located close to the ridge axis or in the immediate vicinity of transform faults. A local seismological network of ocean-bottom seismometers and land stations on and around the archipelago of Tristan da Cunha, allowed for the first time a local earthquake survey for one year. We relate intra-plate seismicity within the African oceanic plate segment north of the island partly to extensional stresses induced by a bordering large transform fault and to the existence of the Tristan mantle plume. The temporal propagation of earthquakes within the segment reflects the prevailing stress field. The strong extensional stresses in addition with the plume weaken the lithosphere and might hint at an incipient ridge jump. An apparently aseismic zone coincides with the proposed location of the Tristan conduit in the upper mantle southwest of the islands. The margins of this zone describe the transition between the ductile and the surrounding brittle regime. Moreover, we observe seismicity close to the islands of Tristan da Cunha and nearby seamounts, which we relate to ongoing tectono-magmatic activity.
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  • 3
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    Ultraslow spreading and volcanism at the eastern end of Gakkel Ridge, Arctic Ocean (2019)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 20 . pp. 6033-6050.
    Details
    Publication Date: 2022-01-31
    Description: Ultraslow spreading ridges are poorly understood plate boundaries consisting of magmatic and amagmatic segments that expose mostly mantle peridotite and only traces of basalt and gabbro. The slowest part of the global spreading system is represented by the eastern Gakkel Ridge in the Central Arctic Ocean, where crustal accretion is characterized by extreme focusing of melt to discrete magmatic centers. Close to its eastern tip lies the unusual 5,310 m deep Gakkel Rift Deep (GRD) with limited sediment infill, which is in strong contrast to the broader sediment‐filled rift valleys to the east and west. Here, we report an 40Ar/39Ar age of 3.65±0.01 Ma for a pillow basalt from a seamount located on the rim the GRD confirming ultraslow spreading rates of ~7 mm/yr close to the Laptev Sea as suggested from aeromagnetic data. Its geochemistry points to an alkaline lava, attributed to partial melting of a source that underwent prior geochemical enrichment. We note that the GRD extracts compositionally similar melts as the sparsely magmatic zone further west but at much slower spreading velocities of only ~6‐7 mm/yr, indicating the widespread occurrence of similarly fertile mantle in the High Arctic. This enriched source differs from sub‐continental lithospheric mantle that influences magmatism along the Western Volcanic Zone (Goldstein et al. 2008) and is similar to metasomatized mantle ‐ shown to influence melt genesis along the Eastern Volcanic Zone.
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  • 4
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    Hot Upper Mantle Beneath the Tristan da Cunha Hotspot From Probabilistic Rayleigh-Wave Inversion and Petrological Modeling (2018)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2022-03-09
    Description: Understanding the enigmatic intraplate volcanism in the Tristan da Cunha region requires knowledge of the temperature of the lithosphere and asthenosphere beneath it. We measured phase-velocity curves of Rayleigh waves using cross-correlation of teleseismic seismograms from an array of ocean-bottom seismometers around Tristan, constrained a region-average, shear-velocity structure, and inferred the temperature of the lithosphere and asthenosphere beneath the hotspot. The ocean-bottom data set presented some challenges, which required data-processing and measurement approaches different from those tuned for land-based arrays of stations. Having derived a robust, phase-velocity curve for the Tristan area, we inverted it for a shear wave velocity profile using a probabilistic (Markov chain Monte Carlo) approach. The model shows a pronounced low-velocity anomaly from 70 to at least 120 km depth. VS in the low velocity zone is 4.1-4.2 km/s, not as low as reported for Hawaii (∼4.0 km/s), which probably indicates a less pronounced thermal anomaly and, possibly, less partial melting. Petrological modeling shows that the seismic and bathymetry data are consistent with a moderately hot mantle (mantle potential temperature of 1,410-1,430°C, an excess of about 50-120°C compared to the global average) and a melt fraction smaller than 1%. Both purely seismic inversions and petrological modeling indicate a lithospheric thickness of 65-70 km, consistent with recent estimates from receiver functions. The presence of warmer-than-average asthenosphere beneath Tristan is consistent with a hot upwelling (plume) from the deep mantle. However, the excess temperature we determine is smaller than that reported for some other major hotspots, in particular Hawaii.
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  • 5
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    Seismostratigraphy of the Siberian Sector of the Arctic Ocean and adjacent Laptev Sea Shelf (2014)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Solid Earth, Wiley, 119(7), pp. 5275-5289, ISSN: 2169-9356
    Details
    Publication Date: 2014-08-18
    Description: A new seismostratigraphic model has been established within the Arctic Ocean adjacent to the East Siberian Shelf on the basis of multichannel seismic reflection data acquired along a transect at 81°N. Ages for the sedimentary units were estimated via links to seismic lines and drill site data of the US Chukchi Shelf, the Lomonosov Ridge, and the adjacent Laptev Shelf. Two distinct seismic units were mapped throughout the area and are the constraints for dating the remaining strata. The lower marker unit, a pronounced high-amplitude reflector sequence (HARS), is the most striking stratigraphic feature over large parts of the Arctic Ocean. It indicates a strong and widespread change in deposition conditions. Probably, it developed during Oligocene times when a reorientation of Arctic Plates took place, accompanied by the gradual opening of the Fram Strait, and a widespread regression of sea level. The top of the HARS likely marks the end of Oligocene/early Miocene (23Ma). An age estimate for the base of the sequence is less clear but likely corresponds to base of Eocene (˜56Ma). The second marked unit detected on the seismic lines parallels the seafloor with a thickness of about 200ms two-way travel time (160 m). Its base is marked by a change from a partly transparent sequence with weak amplitude reflections below to a set of continuous high-amplitude reflectors above. This interface likely marks the transition to large-scale glaciation of the northern hemisphere and therefore is ascribed to the top Miocene (5.3 Ma).
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
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    The Weddell Gyre, Southern Ocean: present knowledge and future challenges (2019)
    Wiley
    In:  EPIC3Reviews of Geophysics, Wiley, 57, ISSN: 8755-1209
    Details
    Publication Date: 2019-08-01
    Description: The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. We review the state‐of‐the art knowledge concerning the WG from an interdisciplinary perspective, uncovering critical aspects needed to understand this system's role in shaping the future evolution of oceanic heat and carbon uptake over the next decades. The main limitations in our knowledge are related to the conditions in this extreme and remote environment, where the polar night, very low air temperatures and presence of sea ice year‐round hamper field and remotely sensed measurements. We highlight the importance of winter and under‐ice conditions in the southern WG, the role that new technology will play to overcome present‐day sampling limitations, the importance of the WG connectivity to the low‐latitude oceans and atmosphere, and the expected intensification of the WG circulation as the westerly winds intensify. Greater international cooperation is needed to define key sampling locations that can be visited by any research vessel in the region. Existing transects sampled since the 1980s along the Prime Meridian and along an East‐West section at ~62°S should be maintained with regularity to provide answers to the relevant questions. This approach will provide long‐term data to determine trends and will improve representation of processes for regional, Antarctic‐wide and global modeling efforts – thereby enhancing predictions of the WG in global ocean circulation and climate.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Deposition history and paleo-current activity on the southeastern Lomonosov Ridge and its Eurasian flank based on seismic data (2020)
    Wiley
    In:  EPIC3Geochemistry, Geophysics, Geosystems, Wiley, 21, pp. #e2020GC009133
    Details
    Publication Date: 2020-11-01
    Description: A regional seismic survey on the southeastern Lomonosov Ridge and adjacent basins provides constraints on the coupled evolution of ocean circulations, depositional regime and tectonic processes. First, Mesozoic strata on the Lomonosov Ridge, its faulted flanks and the initial Amundsen Basin were covered with syn-rift sediments of Paleocene to early Eocene age. Numerous vertical faults indicate differential compaction of possibly anoxic sediments deposited in the young, still isolated Eurasian Basin. The second stage, as indicated by a prominent high-amplitude-reflector sequence (HARS) covering the ridge, was a time of widespread changes in deposition conditions, likely controlled by the ongoing subsidence of the Lomonosov Ridge and gradual opening of the Fram Strait. Episodic incursions of water masses from the North Atlantic probably were the consequences, and led to the deposition of thin sedimentary layers of different lithology. The third stage is marked by continuous deposition since the early Miocene (20 Ma). At that time, the ridge no longer posed an obstacle between the Amerasia and Eurasia Basins and pelagic sedimentation was established. Drift bodies, sediment waves, and erosional structures indicate the onset of circulation. Faulting on the ridge slope has led to a series of terraces where sediment drifts have accumulated since the early Miocene. It is suggested that ongoing sagging of the ridge and currents may have shaped the steep sediment free flanks of the terraces. Lastly, a sequence of high-amplitude reflectors marks the transition to the early Pliocene large-scale Northern Hemisphere glaciations.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Bathymetry beneath ice shelves of western Dronning Maud Land, East Antarctica, and implications on ice shelf stability (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(12), pp. e2019GL086724, ISSN: 0094-8276
    Details
    Publication Date: 2020-09-06
    Description: Antarctica's ice shelves play a key role in stabilizing the ice streams that feed them. Since basal melting largely depends on ice‐ocean interactions, it is vital to attain consistent bathymetry models to estimate water and heat exchange beneath ice shelves. We have constructed bathymetry models beneath the ice shelves of western Dronning Maud Land by inverting airborne gravity data, and incorporating seismic, multibeam and radar depth references. Our models reveal deep glacial troughs beneath the ice shelves and terminal moraines close to the continental shelf breaks, which currently limit the entry of Warm Deep Water from the Southern Ocean. The ice shelves buttress a catchment that comprises an ice volume equivalent to nearly 1 meter of eustatic sea level rise, partly susceptible to ocean forcing. Changes in water temperature and thermocline depth may accelerate marine based ice sheet drainage and constitute an underestimated contribution to future global sea level rise.
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    New Antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in Antarctica (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43(2), pp. 600-610, ISSN: 0094-8276
    Details
    Publication Date: 2017-10-17
    Description: Gravity surveying is challenging in Antarctica because of its hostile environment and inaccessibility. Nevertheless, many ground-based, airborne, and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s. We present the first modern Antarctic-wide gravity data compilation derived from 13 million data points covering an area of 10 million km2, which corresponds to 73% coverage of the continent. The remove-compute-restore technique was applied for gridding, which facilitated leveling of the different gravity data sets with respect to an Earth gravity model derived from satellite data alone. The resulting free-air and Bouguer gravity anomaly grids of 10 km resolution are publicly available. These grids will enable new high-resolution combined Earth gravity models to be derived and represent a major step forward toward solving the geodetic polar data gap problem. They provide a new tool to investigate continental-scale lithospheric structure and geological evolution of Antarctica.
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    Crustal thickness and Vp/Vs ratio in NW Namibia from receiver functions: Evidence for magmatic underplating due to mantle plume-crust interaction (2015)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 42(9), pp. 3330-3337, ISSN: 0094-8276
    Details
    Publication Date: 2015-07-31
    Description: A seismological network was operated at the junction of the aseismic Walvis Ridge with the northwestern Namibian coast. We mapped crustal thickness and bulk Vp/Vs ratio by the H-k analysis of receiver functions. In the Damara Belt, the crustal thickness is ~35 km with a Vp/Vs ratio of 〈1.75. The crust is ~30 km thick at the coast in the Kaoko Belt. Strong variations in crustal thickness and Vp/Vs ratios are found at the landfall of the Walvis Ridge. Here and at ~150 km northeast of the coast, the crustal thickness increases dramatically reaching 44 km and the Vp/Vs ratios are extremely high (~1.89). These anomalies are interpreted as magmatic underplating produced by the mantle plume during the breakup of Gondwana. The area affected by the plume is smaller than 300 km in diameter, possibly ruling out the existence of a large plume head under the continent during the breakup.
    Repository Name: EPIC Alfred Wegener Institut
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