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  • 2015-2019  (277)
  • 2010-2014  (241)
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  • 1
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    The expedition of the research vessel "Polarstern" to the Arctic in 2009 (ARK-XXIV/3) [Elektronische Ressource] (2010)
    Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung
    Associated volumes
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    Call number: ZSP-168-615
    In: Berichte zur Polar- und Meeresforschung
    Description / Table of Contents: Die Polarstern Expedition ARK-XXIV/3 hatte die Seegebiete von Ostgrönland als Zielgebiet. Schwerpunkt der wissenschaftlichen Programme war geowissenschaftliche Forschung zur tektonischen und glazialen Geschichte von Ostgrönland.
    Type of Medium: 12
    Pages: Online-Ressource
    ISSN: 1866-3192
    Series Statement: Berichte zur Polar- und Meeresforschung 615
    URL: http://hdl.handle.net/10013/epic.35320
    Location: AWI Reading room
    Branch Library: AWI Library
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  • 2
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    The offshore East African Rift system: Structural framework at the toe of a juvenile rift (2015)
    Wiley
    In: Tectonics
    Details
    Publication Date: 2015-09-20
    Description: The Cenozoic East African Rift System (EARS) extends from the Red Sea to Mozambique. Here we use seismic reflection and bathymetric data to investigate the tectonic evolution of the offshore branch of the EARS. The data indicate multiple and time-transgressive neotectonic deformations along ~800 km of the continental margin of northern Mozambique. We observe a transition from a mature rift basin in the north to a juvenile fault zone in the south. The respective timing of deformation is derived from detailed seismic stratigraphy. In the north, a ~30 km wide and more than 150 km long, N-S striking symmetric graben initiated as half-graben in the Late Miocene. Extension accelerated in the Pliocene, causing a continuous conjugate border fault and symmetric rift graben. Coevally the rift started to propagate southward, which resulted in a present-day ~30 km-wide half-graben, approximately 200 km further south. Since the Pleistocene, the rift has continued to propagate another ~300 km, where the incipient rift is reflected by sub-recent small-scale normal faulting. Estimates of the overall brittle extension of the matured rift range between 5 and 12 km, with an along-strike southward decrease of the extension rate. The offshore portion of the EARS evolves magma-poor, similar to the onshore western branch. The structural evolution of the offshore EARS is suggested to be related to and controlled by differing inherited lithospheric fabrics. Pre-existing fabrics may not only guide and focus extension but also control rift architecture.
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Seismic transect across the Lomonosov and Mendeleev ridges: Constraints on the geological evolution of the Amerasia Basin, Arctic Ocean (2013)
    Wiley
    Details
    Publication Date: 2013-09-24
    Description: [1]  We report on seismic and petrological data that provide new constraints on the geological evolution of the Amerasia Basin. A seismic reflection profile across the Makarov Basin, located between the Mendeleev and Lomonosov ridges, shows a complete undisturbed sedimentary section of Mesozoic/Cenozoic age. In contrast to the Mendeleev Ridge, the margin of the Lomonosov Ridge is wide and shows horst and graben structures. We suggest that the Mendeleev Ridge is most likely volcanic in origin and support this finding with a 40 Ar/ 39 Ar isotopic age for a tholeitic basalt sampled from the central Alpha/Mendeleev Ridge. Seismic reflection data for the Makarov Basin show no evidence of compressional features consistent with the Lomonosov Ridge moving as a microplate in the Cenozoic. We propose that the Amerasia Basin moved as a single tectonic plate during the opening of the Eurasia Basin.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Repeated Pleistocene glaciation of the East Siberian continental margin (2013)
    Springer Nature
    Details
    Publication Date: 2013-09-28
    Description: Nature Geoscience 6, 842 (2013). doi:10.1038/ngeo1904 Authors: Frank Niessen, Jong Kuk Hong, Anne Hegewald, Jens Matthiessen, Rüdiger Stein, Hyoungjun Kim, Sookwan Kim, Laura Jensen, Wilfried Jokat, Seung-Il Nam & Sung-Ho Kang During the Pleistocene glaciations, Arctic ice sheets on western Eurasia, Greenland and North America terminated at their continental margins. In contrast, the exposed continental shelves in the Beringian region of Siberia are thought to have been covered by a tundra landscape. Evidence of grounded ice on seafloor ridges and plateaux off the coast of the Beringian margin, at depths of up to 1,000 m, have generally been attributed to ice shelves or giant icebergs that spread oceanwards during glacial maxima. Here we identify marine glaciogenic landforms visible in seismic profiles and detailed bathymetric maps along the East Siberian continental margin. We interpret these features, which occur in present water depths of up to 1,200 m, as traces from grounding events of ice sheets and ice shelves. We conclude that the Siberian Shelf edge and parts of the Arctic Ocean were covered by ice sheets of about 1 km in thickness during several Pleistocene glaciations before the most recent glacial period, which must have had a significant influence on albedo and oceanic and atmospheric circulation.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 5
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    Constraints on past plate and mantle motion from new ages for the Hawaiian-Emperor Seamount Chain (2013)
    Wiley
    Details
    Publication Date: 2013-09-12
    Description: Estimates of the relative motion between the Hawaiian and Louisville hotspots have consequences for understanding the role and character of deep Pacific-mantle return flow. The relative motion between these primary hotspots can be inferred by comparing the age records for their seamount trails. We report 40 Ar/ 39 Ar ages for 18 lavas from 10 seamounts along the Hawaiian-Emperor Seamount Chain (HESC), showing that volcanism started in the sharp portion of the Hawaiian-Emperor Bend (HEB) at ≥47.5 Ma and continued for ≥5 Myr. The slope of the along-track distance from the currently active Hawaiian hotspot plotted versus age is constant (57±2 km/Myr) between ~57 and 25 Ma in the central ~1900 km of the seamount chain, including the HEB. This model predicts an age for the oldest Emperor Seamounts that matches published ages, implying that a linear age-distance relationship might extend back to at least 82 Ma. In contrast, Hawaiian age progression was much faster since at least ~15 Ma and possibly as early as ~27 Ma. Linear age-distance relations for the Hawaii-Emperor and Louisville seamount chains predict ~300 km overall hotspot relative motion between 80 and 47.5 Ma, in broad agreement with numerical models of plumes in a convecting mantle, and paleomagnetic data We show that a change in hotspot relative motion may also have occurred between ~55 Ma and ~50 Ma. We interpret this change in hotspot motion as evidence that the HEB reflects a combination of hotspot and plate motion changes driven by the same plate/mantle reorganization.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Deformation-related volcanism in the Pacific Ocean linked to the Hawaiian–Emperor bend (2015)
    Springer Nature
    Details
    Publication Date: 2015-04-30
    Description: Nature Geoscience 8, 393 (2015). doi:10.1038/ngeo2416 Authors: John M. O’Connor, Kaj Hoernle, R. Dietmar Müller, Jason P. Morgan, Nathaniel P. Butterworth, Folkmar Hauff, David T. Sandwell, Wilfried Jokat, Jan R. Wijbrans & Peter Stoffers Ocean islands, seamounts and volcanic ridges are thought to form above mantle plumes. Yet, this mechanism cannot explain many volcanic features on the Pacific Ocean floor and some might instead be caused by cracks in the oceanic crust linked to the reorganization of plate motions. A distinctive bend in the Hawaiian–Emperor volcanic chain has been linked to changes in the direction of motion of the Pacific Plate, movement of the Hawaiian plume, or a combination of both. However, these links are uncertain because there is no independent record that precisely dates tectonic events that affected the Pacific Plate. Here we analyse the geochemical characteristics of lava samples collected from the Musicians Ridges, lines of volcanic seamounts formed close to the Hawaiian–Emperor bend. We find that the geochemical signature of these lavas is unlike typical ocean island basalts and instead resembles mid-ocean ridge basalts. We infer that the seamounts are unrelated to mantle plume activity and instead formed in an extensional setting, due to deformation of the Pacific Plate. 40Ar/39Ar dating reveals that the Musicians Ridges formed during two time windows that bracket the time of formation of the Hawaiian–Emperor bend, 53–52 and 48–47 million years ago. We conclude that the Hawaiian–Emperor bend was formed by plate–mantle reorganization, potentially triggered by a series of subduction events at the Pacific Plate margins.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 7
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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
    Details
    Publication Date: 2015-04-26
    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.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Evidence for ice-free summers in the late Miocene central Arctic Ocean (2016)
    Springer Nature
    Details
    Publication Date: 2016-04-06
    Description: Article Despite the importance of Arctic sea-ice in the global climate system, a paucity of pre-Quaternary sedimentary archives limits our understanding of its long-term history. Here, based on ancient sediments revealed by submarine landslides, the authors reconstruct Arctic sea-ice conditions during the Miocene. Nature Communications doi: 10.1038/ncomms11148 Authors: Ruediger Stein, Kirsten Fahl, Michael Schreck, Gregor Knorr, Frank Niessen, Matthias Forwick, Catalina Gebhardt, Laura Jensen, Michael Kaminski, Achim Kopf, Jens Matthiessen, Wilfried Jokat, Gerrit Lohmann
    Electronic ISSN: 2041-1723
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 9
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    A new bathymetry of the Northeast Greenland continental shelf: constraints on glacial and other processe (2015)
    Wiley
    Details
    Publication Date: 2015-10-14
    Description: A new digital bathymetric model (DBM) for the Northeast Greenland (NEG) continental shelf (74°N to 81°N) is presented. The DBM has a grid cell size of 250 m x 250 m and incorporates bathymetric data from 30 multibeam cruises, more than 20 singlebeam cruises and first reflector depths from industrial seismic lines. The new DBM substantially improves the bathymetry compared to older models. The DBM not only allows a better delineation of previously known seafloor morphology but, in addition, reveals the presence of previously unmapped morphological features including glacially-derived troughs, fjords, grounding-zone wedges and lateral moraines. These submarine landforms are used to infer the past extent and ice-flow dynamics of the Greenland Ice Sheet during the last full-glacial period of the Quaternary and subsequent ice retreat across the continental shelf. The DBM reveals cross-shelf bathymetric troughs that may enable the inflow of warm Atlantic water masses across the shelf, driving enhanced basal melting of the marine-terminating outlet glaciers draining the ice sheet to the coast in Northeast Greenland. Knolls, sinks and hummocky seafloor on the middle shelf are also suggested to be related to salt diapirism. North-south orientated elongate depressions are identified that probably relate to ice-marginal processes in combination with erosion caused by the East Greenland Current. A single guyot-like peak has been discovered and is interpreted to have been produced during a volcanic event approximately 55 Ma ago. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Geophysical evidence for the extent of crustal types and the type of margin along a profile in the northeastern Baffin Bay (2015)
    Wiley
    Details
    Publication Date: 2015-10-24
    Description: Investigating the crust of northern Baffin Bay provides valuable indications for the still debated evolution of this area. The crust of the southern Melville Bay is examined based on wide-angle seismic and gravity data. The resulting P wave velocity, density, and geological models give insights into the crustal structure. A stretched and rifted continental crust underneath southern Melville Bay is up to 30 km thick, with crustal velocities ranging between 5.5 and 6.9 km/s. The deep Melville Bay Graben contains a 9 km thick infill with velocities of 4 to 5.2 km/s in its lowermost part. West of the Melville Bay Ridge, a ~80 km wide and partly only 5 km thick Continent-Ocean Transition (COT) is present. West of the COT, up to 5 km thick sedimentary layers cover a 4.3 to 7 km thick, two-layered oceanic crust. The upper oceanic layer 2 has velocities of 5.2 to 6.0 km/s, the oceanic layer 3 has been modeled with rather low velocities of 6.3 to 6.9 km/s. Low velocities of 7.8 km/s characterize the probably serpentinized upper mantle underneath the thin crust. The serpentinized upper mantle and low thickness of the oceanic crust are another indication for slow or ultraslow spreading during the formation of the oceanic part of the Baffin Bay. By comparing our results on the crustal structure with other wide-angle seismic profiles recently published, differences in the geometry and structure of the crust and the overlying sedimentary cover are revealed. Moreover, the type of margin and the extent of crustal types in the Melville Bay area are discussed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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