A numerical modeling study of the Southern Senegal upwelling shelf: Circulation and upwelling source waters

Abstract

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 crossshore 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.

Interannual variability of Sea Surface Salinity in North-Eastern Tropical Atlantic: influence of freshwater fluxes

“…In the configuration used here, the parent grid covering [7°N-35°N; 30°W-10°W] has a resolution of 10 km, and the child grid used in the Senegal region [12°N-18°N; 20°W-15°W] has a resolution of 2 km. More details on the model configuration can be found in Ndoye et al (2018). Daily outputs from the MERCATOR model output at 1/12° resolution (GLOBAL-ANALYSISFORECAST-PHY-001-024; downloaded from http://marine.copernicus.eu/) are used to force physical properties (temperature, salinity, velocity and sea level) at the open boundary conditions (OBC) of the parent grid.…”

“…In the present study, the model was run with two different precipitation datasets and two different river runoff products, which are detailed in the following. No surface salinity restoring to climatological observations (e.g., Ndoye et al (2018)) was used.…”

Comment on egusphere-2024-818

“…In the configuration used here, the parent grid covering [7°N-35°N; 30°W-10°W] has a resolution of 10 km, and the child grid used in the Senegal region [12°N-18°N; 20°W-15°W] has a resolution of 2 km. More details on the model configuration can be found in Ndoye et al (2018). Daily outputs from the MERCATOR model output at 1/12° resolution (GLOBAL-ANALYSISFORECAST-PHY-001-024; downloaded from http://marine.copernicus.eu/) are used to force physical properties (temperature, salinity, velocity and sea level) at the open boundary conditions (OBC) of the parent grid.…”

Identification and Characterization of Critical Sites for Small Pelagic Fish in the Coastal Marine Area of Senegal, West Africa

“…The effect of topographic features, such as capes and headlands modulates dramatically the onshore movement of upwelled water and favors the formation of stationary coastal upwelling centers (Faye et al, 2015;Capet et al, 2017). The retention of near-shore surface waters plays a major ecological role in the breeding of small pelagic fish (Ndoye et al, 2018).…”

“…High K values for most target species at the Cap de Naze, Mbodiè ne-Ngazobil, and Diakhanor-Sangomar sites could be explained by the advection of upwelled waters arriving in these areas (Capet et al, 2017;Ndoye et al, 2018). To this, could also be added the quality and availability of food in the Petite Côte, an area recognized as one of the richest in primary and secondary production (Diadhiou et al, 2017;Ndour et al, 2018), and very favorable to small pelagics (Diankha et al, 2018).…”