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  • Articles  (471,615)
  • Wiley-Blackwell  (471,615)
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  • 1
    Publication Date: 2024-04-05
    Description: Secondary microseisms recorded by seismic stations are generated in the ocean by the interaction of ocean gravity waves.We present here the theory for modelling secondary microseismic noise by normal mode summation.We show that the noise sources can be modelled by vertical forces and how to derive them from a realistic ocean wave model. We then show how to compute bathymetry excitation effect in a realistic earth model by using normal modes and a comparison with Longuet–Higgins approach. The strongest excitation areas in the oceans depends on the bathymetry and period and are different for each seismic mode. Seismic noise is then modelled by normal mode summation considering varying bathymetry. We derive an attenuation model that enables to fit well the vertical component spectra whatever the station location. We show that the fundamental mode of Rayleigh waves is the dominant signal in seismic noise. There is a discrepancy between real and synthetic spectra on the horizontal components that enables to estimate the amount of Love waves for which a different source mechanism is needed. Finally, we investigate noise generated in all the oceans around Africa and show that most of noise recorded in Algeria (TAM station) is generated in the Northern Atlantic and that there is a seasonal variability of the contribution of each ocean and sea.
    Description: Published
    Description: 1732-1745
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: Surface waves and free oscillations ; Seismic attenuation ; Theoretical seismology ; Wave propagation ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
    Publication Date: 2024-04-05
    Description: Secondary microseismic noise is generated by non-linear interactions between ocean waves at the ocean surface. We present here the theory for computing the site effect of the ocean layer upon body waves generated by noise sources distributed along the ocean surface. By defining the wavefield as the superposition of plane waves, we show that the ocean site effect can be described as the constructive interference of multiply reflected P waves in the ocean that are then converted to either P or SV waves at the ocean–crust interface. We observe that the site effect varies strongly with period and ocean depth, although in a different way for body waves than for Rayleigh waves. We also show that the ocean site effect is stronger for P waves than for S waves. We validate our computation by comparing the theoretical noise body wave sources with the sources inferred from beamforming analysis of the three seismogram components recorded by the Southern California Seismic Network. We use rotated traces for the beamforming analysis, and we show that we clearly detect P waves generated by ocean gravity wave interactions along the track of typhoon Ioke (2006 September). We do not detect the corresponding SV waves, and we demonstrate that this is because their amplitude is too weak.
    Description: Published
    Description: 1096-1106
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: Body waves ; Site effects ; Theoretical Seismology ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Publication Date: 2024-03-22
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 4
    Publication Date: 2024-01-31
    Description: The response of permafrost to submergence can vary between ice-rich late Pleistocene deposits and the thermokarst basins that thawed out during the Holocene. We hypothesize that inundated Alases offshore thaw faster than submerged Yedoma. To test this hypothesis, we estimated depths to the top of ice-bearing permafrost offshore of the Bykovsky Peninsula in northeast Siberia using electrical resistivity surveys. The surveys traversed submerged lagoon deposits, drained and refrozen Alas deposits, and undisturbed Yedoma from the coastline to 373 m offshore. While the permafrost degradation rates of the submerged Yedoma were in the range of similar sites, the submerged Alas permafrost degradation rates were up to 170% faster. Given the abundance of thermokarst basins and lakes along parts of the Arctic coastline, its effect on subsea permafrost degradation must be similarly prevalent. Remote sensing analyses suggest that 54% of lagoons wider than 500 m originated in thermokarst basins.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 5
    Publication Date: 2024-01-31
    Description: Permafrost thaw leads to thermokarst lake formation and talik growth tens of meters deep, enabling microbial decomposition of formerly frozen organic matter (OM). We analyzed two 17-m-long thermokarst lake sediment cores taken in Central Yakutia, Russia. One core was from an Alas lake in a Holocene thermokarst basin that underwent multiple lake generations, and the second core from a young Yedoma upland lake (formed ca. 70 years ago) whose sediments have thawed for the first time since deposition. This comparison provides a glance into OM fate in thawing Yedoma deposits. We analyzed total organic carbon (TOC) and dissolved organic carbon (DOC) content, n-alkanes concentrations, and bacterial and archaeal membrane markers. Furthermore, we conducted one-year-long incubations (4 °C, dark) and measured anaerobic carbon dioxide (CO2) and methane (CH4) production. The sediments from both cores contained little TOC (0.7±0.4 wt%), but DOC values were relatively high, with highest values in the frozen Yedoma lake sediments (1620 mg L-1). Cumulative GHG production after one year was highest in the Yedoma lake sediments (226±212 μg CO2-C gdw-1, 28±36 μg CH4-C gdw-1) and 3 and 1.5 times lower in the Alas lake sediments, respectively (75±76 μg CO2-C gdw-1, 19±29 μg CH4-C gdw-1). The highest CO2 production in the frozen Yedoma lake sediments likely results from decomposition of readily bioavailable OM, while highest CH4 production in the non-frozen top sediments of this core suggests that methanogenic communities established upon thaw. The lower GHG production in the non-frozen Alas lake sediments resulted from advanced OM decomposition during Holocene talik development. Furthermore, we found that drivers of CO2 and CH4 production differ following thaw. Our results suggest that GHG production from TOC-poor mineral deposits, which are widespread throughout the Arctic, can be substantial. Therefore, our novel data are relevant for vast ice-rich permafrost deposits vulnerable to thermokarst formation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 6
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    Wiley-Blackwell
    In:  EPIC3Permafrost and Periglacial Processes, Wiley-Blackwell, 32(1), pp. 59-75, ISSN: 1045-6740
    Publication Date: 2024-01-31
    Description: Thermal erosion is a major mechanism of permafrost degradation, resulting in characteristic landforms. We inventory thermo-erosional valleys in ice-rich coastal lowlands adjacent to the Siberian Laptev Sea based on remote sensing, Geographic Information System (GIS), and field investigations for a first regional assessment of their spatial distribution and characteristics. Three study areas with similar geological (Yedoma Ice Complex) but diverse geomorphological conditions vary in valley areal extent, incision depth, and branching geometry. The most extensive valley networks are incised deeply (up to 35 m) into the broad inclined lowland around Mamontov Klyk. The flat, low-lying plain forming the Buor Khaya Peninsula is more degraded by thermokarst and characterized by long valleys of lower depth with short tributaries. Small, isolated Yedoma Ice Complex remnants in the Lena River Delta predominantly exhibit shorter but deep valleys. Based on these hydrographical network and topography assessments, we discuss geomorphological and hydrological connections to erosion processes. Relative catchment size along with regional slope interact with other Holocene relief-forming processes such as thermokarst and neotectonics. Our findings suggest that thermo-erosional valleys are prominent, hitherto overlooked permafrost degradation landforms that add to impacts on biogeochemical cycling, sediment transport, and hydrology in the degrading Siberian Yedoma Ice Complex.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 7
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    Wiley-Blackwell
    In:  EPIC3Functional Ecology, Wiley-Blackwell, 28, pp. 1482-1493, ISSN: 0269-8463
    Publication Date: 2023-09-15
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Wiley-Blackwell
    In:  EPIC3Oxidative Stress in Aquatic Ecosystems, Oxidative Stress in Aquatic Ecosystems, Wiley-Blackwell, 18 p., pp. 263-280, ISBN: 978-1-4443-3548-4
    Publication Date: 2023-06-21
    Description: The chapter will summarize and critically review metabolic responses to environmental stress and stress effects on energy budgets in mollusks. Metabolic adaptations to environmental stress will be analyzed including alternative energy conserving pathways, aerobic/anaerobic transitions and metabolic arrest. Their role in the efficient use of energy substrates and in the maintenance of cellular homeostasis and redox status will be discussed. General stress effects on energy budget at different organization levels (from the cell to the whole-organism) will be analyzed including energy uptake, assimilation, conversion and expenditure, as well as the metabolic costs associated with stress resistance (including antioxidant protection, chaperone function and damage repair). We will compare metabolic responses to moderate and extreme levels of environmental stressors using temperature, ocean acidification, salinity, oxygen deficiency and toxic metal stress as examples. This chapter will also outline the future research directions to improve our understanding of the stress effects on bioenergetics in mollusks and other invertebrates. Keywords: Stress, metabolic adaptation, metabolic arrest, bioenergetics, cellular defense, energy trade-offs
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 9
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    Wiley-Blackwell
    In:  EPIC3Oxidative Stress in Aquatic Ecosystems, Oxidative Stress in Aquatic Ecosystems, Oxford, Wiley-Blackwell, 524 p., pp. 115-126, ISBN: 978 1 4443 3548 4
    Publication Date: 2023-06-21
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 10
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    Wiley-Blackwell
    In:  EPIC3Wiley-Blackwell, ISBN: 9781444335484
    Publication Date: 2023-06-21
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , peerRev
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