Preprints
https://doi.org/10.5194/egusphere-2024-818
https://doi.org/10.5194/egusphere-2024-818
28 Mar 2024
 | 28 Mar 2024
Status: this preprint is open for discussion.

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

Clovis Thouvenin-Masson, Jacqueline Boutin, Vincent Échevin, Alban Lazar, and Jean-Luc Vergely

Abstract. In tropical regions, the fresh water flux entering the ocean originates primarily from precipitation and, to a lesser extent when considering basin scale averages, from continental rivers. Nevertheless, at regional scale, river flows can have a significant impact on the surface ocean dynamics. Riverine fresh water modifies salinity, and therefore density, stratification and circulation. With its particular coastline, relatively high cumulative river discharge, and the vicinity of Inter Tropical Convergence Zone (ITCZ), the eastern Southern North Tropical Atlantic (e-SNTA) region off Northwest Africa is a particularly interesting location to study the linkage between precipitations, river outflows and Sea Surface Salinity (SSS). Here we focus on the regional e-SNTA SSS seasonal cycle and interannual variability. We quantify the impact of river runoff and precipitation on SSS by means of regional simulations forced by different interannual and climatological river runoffs and precipitation products. The simulated SSS are compared with the Climate Change Initiative (CCI) SSS, in situ SSS from Argo, ships and a coastal mooring, and the GLORYS reanalysis SSS. The analysis of the salinity balance in the mixed layer is conducted to explore the dynamics influencing the SSS variability. Overall, the simulations reproduce well the seasonal cycle and interannual variability despite a positive mean model bias north of 15N. The seasonal cycle is impacted by the phasing of the different runoff products. The mixed layer SSS decrease during the rainy season is mainly driven by precipitation followed by runoff by means of horizontal advection and partly compensated by vertical mixing. In terms of interannual anomalies, river runoffs have a more direct impact on SSS than precipitation. This study highlights the importance of properly constraining river runoff and precipitation to simulate realistic SSS, and the importance of observing SSS in coastal regions to validate such constraints.

Clovis Thouvenin-Masson, Jacqueline Boutin, Vincent Échevin, Alban Lazar, and Jean-Luc Vergely

Status: open (until 23 May 2024)

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Clovis Thouvenin-Masson, Jacqueline Boutin, Vincent Échevin, Alban Lazar, and Jean-Luc Vergely
Clovis Thouvenin-Masson, Jacqueline Boutin, Vincent Échevin, Alban Lazar, and Jean-Luc Vergely

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Short summary
Our research focuses on understanding the impact of river runoff and precipitation on sea surface salinity (SSS) in the eastern Southern North Tropical Atlantic (e-SNTA) region off Northwest Africa. By analyzing regional simulations and observational data, we find that river flows significantly influence SSS variability, particularly after the rainy season. Our findings underscore that a main source of uncertainty to represent SSS variability in this region comes from river runoffs estimates.