Seabed Morphodynamics

A special issue of Geosciences (ISSN 2076-3263).

Deadline for manuscript submissions: closed (31 August 2022) | Viewed by 8081

Special Issue Editor


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Guest Editor
School of Ocean Sciences, Bangor University, Bangor LL57 2DG, UK
Interests: seabed mobility; sediment wave dynamics; glacial landscapes; scour; seabed habitats

Special Issue Information

Dear Colleagues,

Although largely out of sight, the seabed supports a wide array of interconnecting services that increasingly underpin our daily lives. The seabed is instrumental in the delivery of, e.g., food, aggregates, minerals, energy, communications, recreation, genetic materials and biodiversity. The seabed also provides regulating services, including climate, nutrient cycling and flood prevention.

Seabed resources are, however, vulnerable to the effects of a mobile seabed, the consequences of which are predicted to increase due to ocean warming and rising sea level. The bathymetric variation of about 20% of Earth’s seabed has been mapped and used to inform marine spatial planning and decision making on a range of scales. This largely static picture of seabed bathymetry needs to become dynamic with knowledge of redistributing sediments (via, e.g., backscatter data and samples), mobile bedforms, altering habitats and the potential exposure of marine infrastructure.

Consideration of the changes in seabed morphology and in seabed composition over time will be essential in our efforts to maintain seabed integrity during the rapid rise in marine industrialisation. We need to know how rising sea levels, changing storminess, and heightened wave energy can fundamentally affect the rate, location and nature of seabed modification over the coming decades. We also need to take into account that the seabed is often heterogeneous and patchy, and that this complexity is influenced by, and in turn impacts, both physical and biological processes.

Through this collection, we would like to recognise and contribute to the growing need for seabed morphodynamical processes to be better documented, understood and/or predicted. In this fully funded open access format, this knowledge will become freely accessible to all users far beyond the academic, and should help seabed resource management, marine spatial planning and conservation.

Dr. Katrien Van Landeghem
Guest Editor

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Keywords

  • marine conservation
  • marine spatial planning
  • resource management
  • risk assessment
  • seabed habitats
  • seabed infrastructure
  • seabed integrity
  • seabed morphodynamics
  • bathymetry
  • backscatter

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Published Papers (2 papers)

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Research

24 pages, 44222 KiB  
Article
Hydrodynamic Processes Controlling Sand Bank Mobility and Long-Term Base Stability: A Case Study of Arklow Bank
by Shauna Creane, Michael O’Shea, Mark Coughlan and Jimmy Murphy
Geosciences 2023, 13(2), 60; https://doi.org/10.3390/geosciences13020060 - 17 Feb 2023
Cited by 2 | Viewed by 2913
Abstract
Offshore sand banks are an important resource for coastal protection, marine aggregates, and benthic habitats and are the site of many offshore wind farms. Consequently, a comprehensive understanding of the baseline processes controlling sand bank morphodynamics is imperative. This knowledge will aid the [...] Read more.
Offshore sand banks are an important resource for coastal protection, marine aggregates, and benthic habitats and are the site of many offshore wind farms. Consequently, a comprehensive understanding of the baseline processes controlling sand bank morphodynamics is imperative. This knowledge will aid the development of a long-term robust marine spatial plan and help address the environmental instability arising from anthropogenic activities. This study uses a validated, dynamically coupled, two-dimensional hydrodynamic and sediment transport model to investigate the hydrodynamic processes controlling the highly mobile upper layer of Arklow Bank, while maintaining overall long-term bank base stability. The results reveal a flood and ebb tidal current dominance on the west and east side of the bank, respectively, ultimately generating a large anticlockwise residual current eddy encompassing the entire bank. This residual current flow distributes sediment along the full length of the sand bank. The positioning of multiple off-bank anticlockwise residual current eddies on the edge of this cell is shown to influence east–west fluctuations of the upper slopes of the sand bank and act as a control on long-term stability. These off-bank eddies facilitate this type of movement when the outer flows of adjacent eddies, located on both sides of the bank, flow in a general uniform direction. Whereas they inhibit this east–west movement when the outer flows of adjacent eddies, on either side of the bank, flow in converging directions towards the bank itself. These residual eddies also facilitate sediment transport in and out of the local sediment transport system. Within Arklow Bank’s morphological cell, eight morphodynamically and hydrodynamically unique bank sections or ‘sub-cells’ are identified, whereby a complex morphodynamic–hydrodynamic feedback loop is present. The local east–west fluctuation of the upper slopes of the bank is driven by migratory on-bank stationary and transient clockwise residual eddies and the development of ‘narrow’ residual current cross-flow zones. Together, these processes drive upper slope mobility but maintain long-term bank base stability. This novel understanding of sand bank morphodynamics is applicable to bedforms in tidally dominated continental shelf seas outside the Irish Sea. Full article
(This article belongs to the Special Issue Seabed Morphodynamics)
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46 pages, 8683 KiB  
Article
Development and Dynamics of Sediment Waves in a Complex Morphological and Tidal Dominant System: Southern Irish Sea
by Shauna Creane, Mark Coughlan, Michael O’Shea and Jimmy Murphy
Geosciences 2022, 12(12), 431; https://doi.org/10.3390/geosciences12120431 - 23 Nov 2022
Cited by 7 | Viewed by 3782
Abstract
With the recent push for a transition towards a climate-resilient economy, the demand on marine resources is accelerating. For many economic exploits, a comprehensive understanding of environmental parameters underpinning seabed morphodynamics in tidally-dominated shelf seas, and the relationship between local and regional scale [...] Read more.
With the recent push for a transition towards a climate-resilient economy, the demand on marine resources is accelerating. For many economic exploits, a comprehensive understanding of environmental parameters underpinning seabed morphodynamics in tidally-dominated shelf seas, and the relationship between local and regional scale sediment transport regimes as an entire system, is imperative. In this paper, high-resolution, time-lapse bathymetry datasets, hydrodynamic numerical modelling outputs and various theoretical parameters are used to describe the morphological characteristics of sediment waves and their spatio-temporal evolution in a hydrodynamically and morphodynamically complex region of the Irish Sea. Analysis reveals sediment waves in a range of sizes (height = 0.1 to 25.7 m, and wavelength = 17 to 983 m), occurring in water depths of 8.2 to 83 mLAT, and migrating at a rate of 1.1 to 79 m/yr. Combined with numerical modelling outputs, a strong divergence of sediment transport pathways from the previously understood predominantly southward flow in the south Irish Sea is revealed, both at offshore sand banks and independent sediment wave assemblages. This evidence supports the presence of a semi-closed circulatory hydrodynamic and sediment transport system at Arklow Bank (an open-shelf linear sand bank). Contrastingly, the Lucifer–Blackwater Bank complex and associated sediment waves are heavily influenced by the interaction between a dominant southward flow and a residual headland eddy, which also exerts a strong influence on the adjacent banner bank. Furthermore, a new sediment transfer system is defined for offshore independent sediment wave assemblages, whereby each sediment wave field is supported by circulatory residual current cells originating from offshore sand banks. These new data and results improve knowledge of seabed morphodynamics in tidally-dominated shelf seas, which has direct implications for offshore renewable developments and long-term marine spatial planning. Full article
(This article belongs to the Special Issue Seabed Morphodynamics)
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