The southern end of the Canary current system comprises of an original upwelling center that has so far received little attention, the Southern Senegal‐Gambia Upwelling Center (SSUC). We investigate its dynamical functioning by taking advantage of favorable conditions in terms of limited cloud coverage. Analyses and careful examinations of over 1500 satellite images of sea surface temperature scenes contextualized with respect to wind conditions confirm the regularity and stability of the SSUC dynamical functioning (as manifested by the recurrence and persistence of particular SST patterns). The analyses also reveal subtle aspects of its upwelling structure: shelf break cooling of surface waters consistent with internal tide breaking/mixing; complex interplay between local upwelling and the Mauritanian current off the Cape Verde headland; complexity of the inner‐shelf/mid shelf frontal transition. The amplitude of the diurnal cycle suggests that large uncertainties exist in the SSUC heat budget. The studies limitations underscore the need for continuous in situ measurement in the SSUC, particularly of winds.

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.

The northeastern Atlantic hosts the most ventilated subsurface waters of any eastern boundary upwelling system, while coastal upwelling source waters are slightly above hypoxic levels. Anoxic conditions have previously been found offshore inside mesoscale eddies whose core waters undergo oxygen consumption for many months. Based on circumstantial in situ observations, this study demonstrates that the Senegalese coastal ocean is subjected to episodic occurrence of zero dissolved oxygen concentration at depth along with elevated nitrite concentration (11 mmol/m³) and nitrate/nitrite deficit to phosphate, thereby indicating severe anoxia and intense nitrogen loss. The anoxic event was associated with a prolonged upwelling relaxation episode in March 2012 and a nearshore diatom bloom that underwent degradation while being advected offshore in stratified waters. This is consistent with scenarios observed in other upwelling systems (Benguela and California), and such conditions are presumably frequent in the southern part of the Canary system.

The regional ocean circulation along the Southern Senegal shelf is studied using a numerical model for varying forcing fields during the upwelling season (November-May). The main objective is to study the shelf circulation of the marine environment in the Southern Senegal Upwelling Shelf (SSUS), the Lagrangian pathways by which waters are transported to the surface in the upwelling tongue and the fate of these waters. Model results are compared with hydrographic measurements during UPSEN2-ECOAO survey and satellite images datasets. The upwelling source waters and also the warm nearshore waters are analyzed, from a Lagrangian point of view, by computing the paths of particles that are passively advected by the regional ocean model velocity field (ROMS). It was found that the model is capable of representing the main characteristics of the SSUS whose Sea Surface Temperature (SST) patterns and their variability have an important similarities but the assessment of the current simulated by the model is less obvious because of the few available observations. The present results suggest that high frequency of wind has a strong influence over the mesoscale patterns of the cross-shore circulation in association with local topography and the presence of the Cape Verde peninsula. These cross-shore circulations are dominated by an onshore flow around 14.5°N and an offshore flow around 14.1°N. The onshore flow is in agreement with the previous eulerian studies regarding the coastal divergence of the surface flow (upwelling) that was strongly localized within a few tens of kilometers south of the Cape Verde in the Hann Bight. Lagrangian experiments show also very clearly that coastal warm waters are upwelling waters that were advected from Hann Bight and underwent a strong warming by the heat flux from the atmosphere to the ocean in a shallow area (∼10 m); therefore, easy to warm up. All numerical solutions have shown a tendency of upwelling particles remaining on the shelf for more than a month. These results may explain the enrichment of water in the SSUS and suggest the need to consider the whole shelf as a retention area. Key words: Upwelling, ocean circulation, modeling, coastal dynamics, shelf, ROMS.

The Canary current upwelling System (CCS) is one the most productive marine ecosystems. CMIP5 simulations under the RCP8.5 scenario for the end of the 21st century project a modest upwelling‐favorable wind decrease over the CCS southern outpost, that is, the southern senegalese upwelling center (SSUC). We explore the coastal‐scale physical manifestations of climate change in the SSUC through dynamical downscaling of projected changes from nine CMIP5 models selected for their realistic representation of present‐day thermohaline structure. We find that coastal upwelling reduction due to wind changes is projected to be aggravated by geostrophic/pressure adjustments related, in large part, to changes in upper ocean stratification. The reduction could reach 25% of present‐day upwelling rates. The intensity of the poleward boundary current offshore of the SSUC is projected to decrease. Together with upper ocean warming this opens vast possibilities of ecological evolutions with large impact on neighboring societies.