However, the strength of the model lies in its use of a non-arbitrary description of the dependence of vertical turbulent exchange on local stability. By allowing the user complete control over the parameters that control tidal currents, meteorological forcing, nutrient boundary conditions, and the phytoplankton physiological parameters, the model is a suitable tool with which to investigate hypotheses concerning the spatial and temporal variability of mixing and its effects on primary production in shelf seas. Tidal mixing fronts mark the boundaries between these different regions, and they are clearly visible in satellite images of sea surface temperature during summer. The satellite image below, taken on July 12th 1999, shows the tidal mixing fronts around the NW European shelf seas. An example of a tidal mixing front in the image is the Celtic Sea front, stretching between the coasts of SE Eire and SW Wales.
Horizontal advection is only likely to play a role in regions with strong mean flows.
The SeaWIFS satellite image below was taken on the same day as the temperature image above, and shows the high level of surface biomass along the Celtic Sea front. Elevated production within the surface frontal waters requires a source of nutrients to fuel it. Arrow A represents the weak diapycnal nutrient flux into the base of the thermocline on the stratified side of the front. This flux supports production within the subsurface maximum, but production in the surface layer is nutrient-limited. Arrow B represents the increased nutrient flux through the weaker stratification at the front, potentially supporting the near-surface productivity at the front.