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  • 2010-2014  (241)
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  • 1
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    Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung
    Associated volumes
    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
    Location: AWI Reading room
    Branch Library: AWI Library
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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    Publication Date: 2012-04-27
    Description: SUMMARY Baffin Bay represents the northern extension of the extinct rift system in the Labrador Sea. While the extent of oceanic crust and magnetic spreading anomalies are well constrained in the Labrador Sea, no magnetic spreading anomalies have yet been identified in Baffin Bay. Thus, the nature and evolution of the Baffin Bay crust remain uncertain. To clearly characterize the crust in southern Baffin Bay, 42 ocean bottom seismographs were deployed along a 710-km-long seismic refraction line, from Baffin Island to Greenland. Multichannel seismic reflection, gravity and magnetic anomaly data were recorded along the same transect. Using forward modelling and inversion of observed traveltimes from dense airgun shots, a P -wave velocity model was obtained. The detailed morphology of the basement was constrained using the seismic reflection data. A 2-D density model supports and complements the P -wave modelling. Sediments of up to 6 km in thickness with P -wave velocities of 1.8–4.0 km s −1 are imaged in the centre of Baffin Bay. Oceanic crust underlies at least 305 km of the profile. The oceanic crust is 7.5 km thick on average and is modelled as three layers. Oceanic layer 2 ranges in P -wave velocity from 4.8 to 6.4 km s −1 and is divided into basalts and dykes. Oceanic layer 3 displays P -wave velocities of 6.4–7.2 km s −1 . The Greenland continental crust is up to 25 km thick along the line and divided into an upper, middle and lower crust with P -wave velocities from 5.3 to 7.0 km s −1 . The upper and middle continental crust thin over a 120-km-wide continent–ocean transition zone. We classify this margin as a volcanic continental margin as seaward dipping reflectors are imaged from the seismic reflection data and mafic intrusions in the lower crust can be inferred from the seismic refraction data. The profile did not reach continental crust on the Baffin Island margin, which implies a transition zone of 150 km length at most. The new information on the extent of oceanic crust is used with published poles of rotation to develop a new kinematic model of the evolution of oceanic crust in southern Baffin Bay.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
    Publication Date: 2014-11-19
    Description: The interpretation of seismic refraction and gravity data acquired in 2010 gives new insights into the crustal structure of the West Greenland coast and the adjacent deep central Baffin Bay basin. Underneath Melville Bay, the depth of the Moho varies between 26 to 17 km. Stretched continental crust with a thickness of 25 to 14 km and deep sedimentary basins are present in this area. The deep Melville Bay Graben contains an up to ~11 km thick infill of consolidated and unconsolidated sediments with velocities of 1.6 to 4.9 km/s. Seawards, at the ~60 km wide transition between oceanic and stretched continental crust, a mount-shaped magmatic structure is observed, which most likely formed prior to the initial formation of oceanic crust. The up to 4 km high magmatic structure is underlain by a ~2 km thick and ~50 km wide high velocity lower crust. More to the west, in the oceanic part of the Baffin Bay basin, we identify a 2-layered, 3.5 to 6 km thin igneous oceanic crust with increasing thickness toward the shelf. Beneath the oceanic crust, the depth of the Moho ranges between 11.5 and 13.5 km. In the western part of the profile, oceanic layer 3 is unusually thin (~1.5 km) A possible explanation for the thin crust is accretion due to slow spreading, although the basement is notably smooth compared to the basement of other regions formed by ultra-slow spreading. The oceanic crust is underlain by partly serpentinized upper mantle with velocities of 7.6 to 7.8 km/s.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2013-03-12
    Description: [1]  Ultraslow spreading mid-ocean ridges have a low magma budget and melt is distributed unevenly along the ridge axis. There is little or no basaltic crust between isolated magmatic centers. The processes that focus melts to segments of robust magmatism are not yet understood. During a seismic survey of the ultraslow spreading Knipovich Ridge in the Norwegian-Greenland Sea with ocean bottom seismometers, we discovered a seismic gap in the upper mantle beneath Logachev Seamount, where micro-earthquakes clearly delineate a shallowing of the maximum depth of faulting. A topography of the lithosphere that allows melts to travel laterally along its base and rise in areas of thin lithosphere has been proposed as possible mechanism to explain the focusing of melts at volcanic centers, but has never been confirmed observationally. Our results are the first geophysical evidence for an along-axis variation of the lithospheric thickness at an ultraslow spreading ridge.
    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
    Publication Date: 2013-07-10
    Description: [1]  The interpretation of tectonic and sedimentary structures in the northern Chukchi region, Arctic Ocean, is important to enhance our understanding of the tectonic evolution of this region. Therefore, multi-channel seismic lines as well as seismic wide-angle reflection and refraction data were acquired in the northern Chukchi region during the RV Polarstern ARK-XXIII/3 summer expedition in 2008. These data have been processed and interpreted for the three main geological provinces (Chukchi Plateau, Chukchi Abyssal Plain and Mendeleev Ridge) to describe the sedimentary and basement structures of the northern Chukchi region. Furthermore, using the age control of five exploration wells drilled near the coast of Alaska in combination with additional seismic reflection lines located on the Chukchi Shelf, we were able to date sediment horizons within the research area. In total, six sediment horizons with ages between Barremian/Hauterivian and the Top Miocene were identified. Especially the Top Oligocene horizon forms a pronounce unconformity on the Chukchi Plateau and on the Mendeleev Ridge flanks. The origin of this unconformity can be associated with the opening of the Fram Strait indicating a significant change in the Arctic Ocean current system.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2014-06-04
    Description: In multibeam echosounder and sub-bottom profiler data acquired during RV Polarstern cruise ARK-VII/3a from the Hovgaard Ridge (Fram Strait), we found evidence for very deep (〉1200 m) iceberg scouring. Five elongated seafloor features have been detected that are interpreted to be iceberg scours. The scours are oriented in north-south/south-north direction and are about 15 m deep, 300 m wide, and 4 km long crossing the entire width of the ridge. They are attributed to multiple giant palaeo-icebergs that most probably left the Arctic Ocean southward through Fram Strait. The huge keel-depths are indicative of ice sheets extending into the Arctic Ocean being at least 1200 m thick at the calving front during glacial maxima. The deep St Anna Trough or grounded ice observed at the East Siberian Continental Margin are likely source regions of these icebergs that delivered freshwater to the Nordic Seas.
    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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  • 10
    Publication Date: 2014-06-13
    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 (23 Ma). An age estimate for the base of the sequence is less clear, but likely corresponds to base of Eocene (˜56 Ma). The second marked unit detected on the seismic lines parallels the seafloor with a thickness of about 200 ms 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).
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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