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  • Christiansen, Nils  (4)
  • 1
    Online Resource
    Online Resource
    Frontiers Media SA ; 2022
    In:  Frontiers in Marine Science Vol. 9 ( 2022-2-3)
    In: Frontiers in Marine Science, Frontiers Media SA, Vol. 9 ( 2022-2-3)
    Abstract: The potential impact of offshore wind farms through decreasing sea surface wind speed on the shear forcing and its consequences for the ocean dynamics are investigated. Based on the unstructured-grid model SCHISM, we present a new cross-scale hydrodynamic model setup for the southern North Sea, which enables high-resolution analysis of offshore wind farms in the marine environment. We introduce an observational-based empirical approach to parameterize the atmospheric wakes in a hydrodynamic model and simulate the seasonal cycle of the summer stratification in consideration of the recent state of wind farm development in the southern North Sea. The simulations show the emergence of large-scale attenuation in the wind forcing and associated alterations in the local hydro- and thermodynamics. The wake effects lead to unanticipated spatial variability in the mean horizontal currents and to the formation of large-scale dipoles in the sea surface elevation. Induced changes in the vertical and lateral flow are sufficiently strong to influence the residual currents and entail alterations of the temperature and salinity distribution in areas of wind farm operation. Ultimately, the dipole-related processes affect the stratification development in the southern North Sea and indicate potential impact on marine ecosystem processes. In the German Bight, in particular, we observe large-scale structural change in stratification strength, which eventually enhances the stratification during the decline of the summer stratification toward autumn.
    Type of Medium: Online Resource
    ISSN: 2296-7745
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 2757748-X
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  • 2
    Online Resource
    Online Resource
    Frontiers Media SA ; 2023
    In:  Frontiers in Marine Science Vol. 10 ( 2023-5-12)
    In: Frontiers in Marine Science, Frontiers Media SA, Vol. 10 ( 2023-5-12)
    Abstract: Structure drag from offshore wind turbines and its physical impacts on the marine environment of the German Bight are investigated in this study. The flow past vertical cylinders, such as wind turbine foundations, and associated turbulent mixing has long been studied, but questions remain about anticipated regional implications of offshore wind infrastructure on physical and biogeochemical conditions. Here, we present two existing modeling approaches for simulating wind turbine foundation effects in regional ocean models and discuss the problematic use of very high resolution in hydrostatic modeling. By implementing a low-resolution structure drag parameterization in an unstructured-grid model, we demonstrate the impacts of monopile drag on hydrodynamic conditions, validated against recent in-situ measurements. Although the anthropogenic mixing is confined at wind farm sites, our simulations show that structure-induced mixing affects much larger, regional scales. The additional turbulence production emerges as the driving mechanism behind the monopile impacts, leading to changes in both the current velocities and stratification, with magnitudes of about 10%, similar in magnitude to regional annual and interannual variabilities. This study provides new insights into the hydrodynamic impact of offshore wind farms at their current development levels and emphasizes the need for further research in view of potential restructuring of the future coastal environment.
    Type of Medium: Online Resource
    ISSN: 2296-7745
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2023
    detail.hit.zdb_id: 2757748-X
    Location Call Number Limitation Availability
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  • 3
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2022
    In:  Communications Earth & Environment Vol. 3, No. 1 ( 2022-11-24)
    In: Communications Earth & Environment, Springer Science and Business Media LLC, Vol. 3, No. 1 ( 2022-11-24)
    Abstract: The wind wake effect of offshore wind farms affects the hydrodynamical conditions in the ocean, which has been hypothesized to impact marine primary production. So far only little is known about the ecosystem response to wind wakes under the premisses of large offshore wind farm clusters. Here we show, via numerical modeling, that the associated wind wakes in the North Sea provoke large-scale changes in annual primary production with local changes of up to ±10% not only at the offshore wind farm clusters, but also distributed over a wider region. The model also projects an increase in sediment carbon in deeper areas of the southern North Sea due to reduced current velocities, and decreased dissolved oxygen inside an area with already low oxygen concentration. Our results provide evidence that the ongoing offshore wind farm developments can have a substantial impact on the structuring of coastal marine ecosystems on basin scales.
    Type of Medium: Online Resource
    ISSN: 2662-4435
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2022
    detail.hit.zdb_id: 3037243-4
    Location Call Number Limitation Availability
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  • 4
    Online Resource
    Online Resource
    Frontiers Media SA ; 2022
    In:  Frontiers in Marine Science Vol. 9 ( 2022-10-3)
    In: Frontiers in Marine Science, Frontiers Media SA, Vol. 9 ( 2022-10-3)
    Abstract: With increasing offshore wind development, more and more marine environments are confronted with the effects of atmospheric wind farm wakes on hydrodynamic processes. Recent studies have highlighted the impact of the wind wakes on ocean circulation and stratification. In this context, however, previous studies indicated that wake effects appear to be attenuated in areas strongly determined by tidal energy. In this study, we therefore determine the role of tides in wake-induced hydrodynamic perturbations and assess the importance of the local hydrodynamic conditions on the magnitude of the emerging wake effects on hydrodynamics. By using an existing high-resolution model setup for the southern North Sea, we performed different scenario simulations to identify the tidal impact. The results show the impact of the alignment between wind and ocean currents in relation to the hydrodynamic changes that occur. In this regard, tidal currents can deflect emerging changes in horizontal surface currents and even mitigate the mean changes in horizontal flow due to periodic perturbations of wake signals. We identified that, particularly in shallower waters, tidal stirring influences how wind wake effects translate to changes in vertical transport and density stratification. In this context, tidal mixing fronts can serve as a natural indicator of the expected magnitude of stratification changes due to atmospheric wakes. Ultimately, tide-related hydrodynamic features, like periodic currents and mixing fronts, influence the development of wake effects in the coastal ocean. Our results provide important insights into the role of hydrodynamic conditions in the impact of atmospheric wake effects, which are essential for assessing the consequences of offshore wind farms in different marine environments.
    Type of Medium: Online Resource
    ISSN: 2296-7745
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 2757748-X
    Location Call Number Limitation Availability
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