On the Dynamics of the Southern Senegal Upwelling Center: Observed Variability from Synoptic to Superinertial Scales

Upwelling off southern Senegal and Gambia takes place over a wide shelf with a large area where depths are shallower than 20 m. This results in typical upwelling patterns that are distinct (e.g., more persistent in time and aligned alongshore) from those of other better known systems, including Oregon and Peru where inner shelves are comparatively narrow. Synoptic to superinertial variability of this upwelling center is captured through a 4-week intensive field campaign, representing the most comprehensive measurements of this region to date. The influence of mesoscale activity extends across the shelf break and far over the shelf where it impacts the midshelf upwelling (e.g., strength of the upwelling front and circulation), possibly in concert with wind fluctuations. Internal tides and solitary waves of large amplitude are ubiquitous over the shelf. The observations suggest that these and possibly other sources of mixing play a major role in the overall system dynamics through their impact upon the general shelf thermohaline structure, in particular in the vicinity of the upwelling zone. Systematic alongshore variability in thermohaline properties highlights important limitations of the 2D idealization framework that is frequently used in coastal upwelling studies.