Abstract
AbstractThe North West European Shelf break acts as a barrier to the transport and exchange between the open ocean and the shelf seas. The strong spatial variability of these exchange processes is hard to fully explore using observations, and simulations generally are too coarse to simulate the fine‐scale processes over the whole region. In this context, under the FASTNEt program, a new NEMO configuration of the North West European Shelf and Atlantic Margin at 1/60° (∼1.8 km) has been developed, with the objective to better understand and quantify the seasonal and interannual variability of shelf break processes. The capability of this configuration to reproduce the seasonal cycle in SST, the barotropic tide, and fine‐resolution temperature profiles is assessed against a basin‐scale (1/12°, ∼9 km) configuration and a standard regional configuration (7 km resolution). The seasonal cycle is well reproduced in all configurations though the fine‐resolution allows the simulation of smaller scale processes. Time series of temperature at various locations on the shelf show the presence of internal waves with a strong spatiotemporal variability. Spectral analysis of the internal waves reveals peaks at the diurnal, semidiurnal, inertial, and quarter‐diurnal bands, which are only realistically reproduced in the new configuration. Tidally induced pycnocline variability is diagnosed in the model and shown to vary with the spring neap cycle with mean displacement amplitudes in excess of 2 m for 30% of the stratified domain. With sufficiently fine resolution, internal tides are shown to be generated at numerous bathymetric features resulting in a complex pycnocline displacement superposition pattern.
Highlights
Fine-scale and high-frequency dynamical processes are defining features of the coastal and shelf seas
The use of sigma-coordinates in the regional configurations allow a finer vertical resolution at surface and subsurface than the z coordinates in the basin-scale configuration (Figure 6). This is true on the shelf, where the vertical resolution at the thermocline depth (40–60 m) is almost twice finer than in Northern North Atlantic (NNA): between 3 and 4 m of resolution for the regional configurations against 6– 8 m in NNA. Such vertical grid allow the resolution of the internal waves, which have a mean amplitude of 5 m (Table 2), with maximum amplitude up to 28 m, that is four to five grid cells
A basin-scale configuration and two regional NEMO ocean model configurations, focusing on the NW European Shelf, are assessed in order to evaluate the improvement brought to the reproduction of highfrequency processes by horizontal resolution at the kilometric scale
Summary
Fine-scale and high-frequency dynamical processes are defining features of the coastal and shelf seas. As a result of high levels of phytoplankton production, the NW European continental shelf accounts for almost a third of the North Atlantic Ocean carbon uptake (Frankignoulle & Borges, 2001) This carbon can be exported below the summer thermocline (through mixing and sedimentation) where it is either buried, transported to deep water off shelf or outgassed to the atmosphere following subsequent winter mixing. The highly productive seas of the NW European continental shelf support substantial fishing efforts (Pinnegar et al, 2002) and its ecosystems are vulnerable to direct anthropogenic impacts from the populous, industrialized countries at its margins (e.g., through coastal Eutrophication) This vulnerability is acknowledged in the various policy measures enacted to maintain Good Environmental Status of these seas (e.g., the EU’s Marine Strategy Framework Directive).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
