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  • Weitere Quellen  (115)
  • Artikel (OceanRep)  (115)
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  • 2020-2022
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  • 1
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    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 14 (6). pp. 1693-1702.
    Publikationsdatum: 2017-01-09
    Beschreibung: Axial volcanic ridges (AVRs) are found on most slow-spreading mid-ocean ridges and are thought to be the main locus of volcanism there. In this study we present high-resolution mapping of a typical, well-defined AVR on the Mid-Atlantic Ridge at 45°N. The AVR is characterized by “hummocky terrain,” composed typically of hummocks with pillowed or elongate pillowed flanks with pillowed or lobate lava flow summits, often with small haystacks sitting on their highest points. The AVR is surrounded by several areas of “flat seafloor,” composed of lobate and sheet lava flows. The spatial and morphological differences between these areas indicate different eruption processes operating on and off the AVR. Volcanic fissures are found all around and on the AVR, although those with the greatest horizontal displacement are found on the ridge crest and flat seafloor. Clusters of fissures may represent volcanic vents. Extremely detailed comparisons of sediment coverage and examination of contact relations around the AVR suggest that many of the areas of flat seafloor are of a similar age or younger than the hummocky terrain of the AVR. Additionally, all the lavas surveyed have similar degrees of sediment cover, suggesting that the AVR was either built or resurfaced in the same 50 ka time frame as the flat seafloor.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2016-12-01
    Beschreibung: Marine myxobacteria (Enhygromyxa, Plesiocystis, Pseudoenhygromyxa, Haliangium) are phylogenetically distant from their terrestrial counterparts. Salimabromide is the first natural product from the Plesiocystis/Enhygromyxa clade of obligatory marine myxobacteria. Salimabromide has a new tetracyclic carbon skeleton, comprising a brominated benzene ring, a furano lactone residue, and a cyclohexane ring, bridged by a seven-membered cyclic moiety. The absolute configuration was deduced from experimental and calculated CD data. Salimabromide revealed antibiotic activity towards Arthrobacter cristallopoietes.
    Materialart: Article , PeerReviewed
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    Standort Signatur Erwartet Verfügbarkeit
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  • 3
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    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 40 (19). pp. 5159-5163.
    Publikationsdatum: 2017-09-01
    Beschreibung: Methane is a potent greenhouse gas and large-scale rapid release of methane from hydrate may have contributed to past abrupt climate change inferred from the geological record. The discovery in 2008 of over 250 plumes of methane gas escaping from the seabed of the West Svalbard continental margin at ~400 m water depth (mwd) suggests that hydrate is dissociating in the present-day Arctic. Here we model the dynamic response of hydrate-bearing sediments over a period of 2300 years and investigate ocean warming as a possible cause for present-day and likely future dissociation of hydrate, within 350–800 mwd, west of Svalbard. Future temperatures are given by two climate models, HadGEM2 and CCSM4, and scenarios, Representative Concentration Pathways (RCPs) 8.5 and 2.6. Our results suggest that over the next three centuries 5.3–29 Gg yr−1 of methane may be released to the Arctic Ocean on the West Svalbard margin.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
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    Wiley
    In:  Journal of Raman Spectroscopy, 45 (1). pp. 133-138.
    Publikationsdatum: 2017-09-14
    Beschreibung: This article compares the quality of Raman images obtained using metallurgical and oil immersion objectives to map complex structures in two and three dimensions. While the performance of these objectives for depth profiling planar structures has been discussed at length in the literature, the same comparison has not yet been made for 3D mapping of complex objects, where additional complications are introduced by non-planar geometries. Studying samples with increasing complexity shows that the oil immersion objective is strongly preferred because it yields brighter images with better contrast, and eliminates some new and confusing artefacts that do not arise with simple planar objects.
    Materialart: Article , PeerReviewed
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    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2020-07-20
    Beschreibung: Based on quantitative X-ray diffraction mineralogical analysis of cores HU2008029-0006/0008 (857-m water depth) located south of the Davis Strait sill, we seek answers to two questions: (i) the temporal correlation of NW Labrador Shelf Sea Heinrich (H-) and Baffin Bay detrital carbonate (BBDC) events, and (ii) the provenance of the sediments? A sediment-unmixing model (SedUnMix) is used to determine provenance variations. Although 12 radiocarbon dates were obtained there were many age reversals and we favour a depth/age model for HU2008029-0008PC based on correlations to well-dated neighbouring cores north and south of Davis Strait. We find no correlation between H- and BBDC events except for H-0, which appears to be a broadly synchronous event along the NE Canadian margin and is correlative with an episode of major moraine building along this flank of the Laurentide Ice Sheet. Unmixing of the sediment composition based on six potential glacial source regions indicates that the bulk of the sediment in 0008PC is derived from glacial erosion of West Greenland, but is punctuated by intervals when dolomite-rich sediments, derived from outcrops north of Baffin Bay, dominate the composition. Estimated dates on these BBDC events are -13, 25 and 30–38 cal ka BP.
    Materialart: Article , PeerReviewed
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  • 6
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    Wiley
    In:  Wiley Interdisciplinary Reviews: Climate Change, 5 (2). pp. 281-290.
    Publikationsdatum: 2018-02-21
    Beschreibung: Geoengineering, especially its potentially fast and high-leverage versions, is often justified as a necessary response to possible future climate emergencies. In this article, we take the notion of ‘necessity’ in international law as a starting point in assessing how rapid, high-leverage geoengineering might be justified legally. The need to specify reliably ‘grave and imminent peril’ makes such a justification difficult because our scientific ability to predict abrupt climate change, for example, as tipping elements, is limited. The time it takes to establish scientific consensus as well as policy acceptance restricts the scope for effective forewarning and so pre-emptive justifications for geoengineering become more tempting. While recognizing that dangerous, large-scale impacts of climate change is becoming increasingly difficult to avoid, the pre-emptive, emergency frame is problematic. We suggest that arguments from emergency operate on a high level of uncertainty and tend toward hubristic attempts to shape the future, as well as tending to close down rather than open up space for deliberation. We conclude that the emergency frame is not likely to go away, that ignoring or repressing it is a dangerous response, and that more effort is required to defuse and disarm emergency rhetoric.
    Materialart: Article , PeerReviewed
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    Standort Signatur Erwartet Verfügbarkeit
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  • 7
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    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 14 (5). pp. 1523-1537.
    Publikationsdatum: 2018-02-27
    Beschreibung: Understanding the pre-anthropogenic Pb cycle of central North Pacific deep water has attracted a lot of attention in recent years, partly because of its unique geographical location in that it is a remote gyre system characterized by high dust fluxes and sluggish overturning circulation. However, the factors controlling Pb isotope evolution in this area over the Cenozoic are still controversial and various mechanisms have been proposed in previous studies. Here we report new Pb and Nd isotope time series of four ferromanganese crusts (two from the western Pacific near the Mariana arc and the other two from the central Pacific). Together with previously published records, we discuss for the first time the significance of a persistent and systematic Pb isotopic provinciality recorded by central North Pacific crusts over the Cenozoic. We propose that globally well mixed stratosphere volcanic aerosols could contribute Pb but have not been the major factors controlling the Pb isotope distribution in the central North Pacific over time. Island arc input (and probably enhanced hydrothermal input between about 45 and 20 Ma) likely controlled the Pb isotope provinciality and evolution prior to ~20 Ma, when coeval Pb isotope records in different crusts showed large differences and atmospheric silicate dust flux was extremely low. After the Eocene, in particular after 20 Ma, Asian dust input has become an isotopically resolvable source, while island arc-derived Pb has remained important to balance the dust input and to produce the observed Pb isotope distribution in the central North Pacific during this period.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
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    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 118 . pp. 2761-2773.
    Publikationsdatum: 2018-02-27
    Beschreibung: A realistic primitive-equation model of the Southern Ocean at eddying spatial resolution is used to examine the effect of ocean-surface-velocity dependence of the wind stress on the strength of near-inertial oscillations. Accounting for the ocean-surface-velocity dependence of the wind stress leads to a large reduction of wind-induced near-inertial energy of approximately 40 percent and of wind power input into the near-inertial frequency band of approximately 20 percent. A large part of this reduction can be explained by the leading-order modification to the wind stress if the ocean-surface velocity is included. The strength of the reduction is shown to be modulated by the inverse of the ocean-surface-mixed-layer depth. We conclude that the effect of surface-velocity dependence of the wind stress should be taken into account when estimating the wind-power input into the near-inertial frequency band and when estimating near-inertial energy levels in the ocean due to wind forcing.
    Materialart: Article , PeerReviewed
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  • 9
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    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 27 (4). pp. 1236-1245.
    Publikationsdatum: 2016-05-02
    Beschreibung: Stratospheric ozone depletion and emission of greenhouse gases lead to a trend of the southern annular mode (SAM) toward its high-index polarity. The positive phase of the SAM is characterized by stronger than usual westerly winds that induce changes in the physical carbon transport. Changes in the natural carbon budget of the upper 100 m of the Southern Ocean in response to a positive SAM phase are explored with a coupled ecosystem-general circulation model and regression analysis. Previously overlooked processes that are important for the upper ocean carbon budget during a positive SAM period are identified, namely, export production and downward transport of carbon north of the polar front (PF) as large as the upwelling in the south. The limiting micronutrient iron is brought into the surface layer by upwelling and stimulates phytoplankton growth and export production but only in summer. This leads to a drawdown of carbon and less summertime outgassing (or more uptake) of natural CO2. In winter, biological mechanisms are inactive, and the surface ocean equilibrates with the atmosphere by releasing CO2. In the annual mean, the upper ocean region south of the PF loses more carbon by additional export production than by the release of CO2 into the atmosphere, highlighting the role of the biological carbon pump in response to a positive SAM event.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
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    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 27 (1). pp. 11-20.
    Publikationsdatum: 2016-05-02
    Beschreibung: We combined data sets of measured sedimentary calcium carbonate (CaCO3) and satellite-derived pelagic primary production to parameterize the relation between CaCO3 content on the Antarctic shelves and primary production in the overlying water column. CaCO3 content predicted in this way was in good agreement with the measured data. The parameterization was then used to chart CaCO3 content on the Antarctic shelves all around the Antarctic, using the satellite-derived primary production. The total inventory of CaCO3 in the bioturbated layer of Antarctic shelf sediments was estimated to be 0.5 Pg C. This quantity is comparable to the total CO2 uptake by the Southern Ocean in only one to a few years (dependent on the uptake estimate and area considered), indicating that the dissolution of these carbonates will neither delay ocean acidification in this area nor augment the Southern Ocean CO2 uptake capacity.
    Materialart: Article , PeerReviewed
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    Standort Signatur Erwartet Verfügbarkeit
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