Hydrodynamic variability in the Southern Bight of the North Sea in response to typical atmospheric and tidal regimes. Benefit of using a high resolution model

Abstract

In this paper, the hydrodynamics of the Southern Bight of the North Sea (SBNS) and in particular, the Belgian Coastal Zone (BCZ) is investigated on daily to seasonal time scales using a high resolution hydrodynamical model. The Regional Ocean Modeling System (ROMS) is implemented over the SBNS with 5 km resolution and downscaled at 1 km resolution over the BCZ in a two-way nesting configuration run over a three years period (i.e. 2006-2008). The benefit of using a high resolution model over the BCZ is assessed through an extensive comparison of model results with data from satellite and in-situ fixed platforms as well as reference products available for the region. The validation exercise and the results analysis are conducted with a particular focus on hydrodynamic features that are expected to impact the sediment transport. We find that despite the validation procedure does not allow to clearly demonstrate better performance of the high resolution model compared to the coarse resolution model in terms of overtidal circulation, sea surface temperature (SST) and salinity (SSS), the high resolution model resolves additional details in the variability of residual circulation and Scheldt salinity plume dynamics. The analysis of the response of the simulated hydrodynamics to atmospheric regimes for neap and spring tide highlights the major role played by the wind direction on the averaged currents and plume extension. The strongest currents and minimum plume extension are obtained under southwestern winds and neap tide while when northeastern winds prevail, the plume extension is at its maximum and the circulation is the weakest. We show that while neap tides allow the establishment of streamlined circulation, the spring tides induce more turbulent circulation which can favor the retention of transported elements. This latter property could not be resolved with the 5 km resolution model.

Offshore Windfarm Footprint of Sediment Organic Matter Mineralization Processes

“…For both scenarios of OWF development, extended halo's of altered benthic processing were mostly situated to the northeast of the OWFs (e.g., see Figure 4A), in line with the main direction of the residual current present in the region (Supplementary Figure 3: current rosette; Ivanov et al, 2020). Since OWFs act as filters of OM that locally shunt OM from the water column to the sediment, water transported further NE became relatively depleted of OM compared to the baseline (Ivanov et al, 2021).…”

“…The annual cycle of OM deposition was modeled using the COAWST model framework (Warner et al, 2010), consisting of: a three-dimensional hydrodynamic model (ROMS; Regional Ocean Modeling System), a module describing OM and mineral particle dynamics through the water column and sediment bed (CCSTM; Community Coastal Sediment Transport Module), and a module for wave activity (SWAN; Simulating Waves Nearshore) (Supplementary Figure 2). The COAWST model was solved with a horizontal resolution of 5 km, downscaled to 1 km over the BPNS using a two-way nesting procedure (Ivanov et al, 2020). The ROMS module was configured and validated for the modeling domain by Ivanov et al (2020), whereas implementation and validation and the CCSTM and SWAN modules were performed by Ivanov et al (2021).…”

“…The COAWST model was solved with a horizontal resolution of 5 km, downscaled to 1 km over the BPNS using a two-way nesting procedure (Ivanov et al, 2020). The ROMS module was configured and validated for the modeling domain by Ivanov et al (2020), whereas implementation and validation and the CCSTM and SWAN modules were performed by Ivanov et al (2021). For clarity, fundamentals of the CCSTM and SWAN modules are noted below, while for details we refer to Ivanov et al, in press.…”

“…In this research, we model the potential effects of increased carbon deposition related to filtration by fouling fauna in OWFs on benthic mineralization processes. To do so, we used output generated by Ivanov et al (2021) who implemented a model describing filtration by blue mussels on turbine substructures in a hydrodynamic model of the Southern North Sea, including the full BPNS and parts of the bordering French and Dutch coastal zones (Figure 1; Ivanov et al, 2020). In biomass, M. edulis is by far the dominant species present on turbine foundations (Joschko et al, 2008;Krone et al, 2013).…”

Offshore Wind Farm Footprint on Organic and Mineral Particle Flux to the Bottom

“…However, along the Belgian coast the flow can be perpendicular and even opposite due to the complex bathymetry and river inputs (Delhez and Carabin, 2001). In the winter, the main residual current is faster due to the influence of dominant SW winds (Ivanov et al, 2020), which expose the European coast to strong waves originating predominantly from the Dover strait (Neill and Hashemi, 2013). Those waves break at the shallow depths of the BCZ and play an important role in sediment resuspension (10% of the total bottom erosion in the BCZ; Fettweis and Van den Eynde, 2003).…”