Seasonal variability of freshwater plumes in the eastern Gulf of Guinea as inferred from satellite measurements.

Type Article
Date 2021-05
Language English
Author(s) Houndegnonto OdilonORCID1, Kolodziejczyk NicolasORCID6, Maes ChristopheORCID1, Bourlès BernardORCID2, Da Allada C. Y.ORCID3, 4, 5, Reul NicolasORCID7
Affiliation(s) 1 : University of Brest (UBO) IRD CNRS Ifremer Laboratoire d’Océanographie Physique et Spatiale (LOPS, UMR 6523) Brest, France
2 : US IMAGO (IRD) Brest ,France
3 : LaGEA/ENSTP/UNSTIM Abomey ,Benin
4 : ICMPA‐UNESCO Chair/UAC Cotonou ,Benin
5 : LHMC/IRHOB Cotonou ,Benin
6 : University of Brest (UBO) IRD CNRS Ifremer Laboratoire d’Océanographie Physique et Spatiale (LOPS, UMR 6523) Brest, France
7 : University of Brest (UBO) IRD CNRS Ifremer Laboratoire d’Océanographie Physique et Spatiale (LOPS, UMR 6523) Brest, France
Source Journal Of Geophysical Research-oceans (2169-9275) (American Geophysical Union (AGU)), 2021-05 , Vol. 126 , N. 5 , P. e2020JC017041 (27p.)
DOI 10.1029/2020JC017041
WOS© Times Cited 1
Keyword(s) freshwater plumes, Gulf of Guinea, rivers runoff, SSS seasonal variability
Abstract

In the eastern Gulf of Guinea (GG), freshwater originated from rivers discharges into the ocean and high precipitation rate are key contributors to the upper ocean vertical density stratification, and play a key role in modulating local air‐sea interactions as well as biogeochemical cycle. Nevertheless, the dynamics of the GG freshwater plumes remain poorly documented because of the scarcity of historical, in situ observations and the lack of an ad hoc satellite‐based analysis in this region. Recent advances in remote sensing capabilities from the Soil Moisture and Ocean Salinity (SMOS) satellite mission offer unprecedented coverage and spatiotemporal resolution of Sea Surface Salinity (SSS) in the GG. Using SMOS SSS and available in situ measurements, the seasonal variability of freshwater plumes and associated physical mechanisms controlling their seasonal cycle are presented and analyzed. Freshwater plumes in the GG follow two dynamical regimes. They present maximum offshore extension during boreal winter and exhibit minimum signature during summer. In the northeastern GG, SSS variability is mainly explained by high precipitation rate and Niger River runoff during winter, while during late summer, SSS is mainly driven by horizontal advection. In contrast, southeast of GG, freshwater plumes are mainly supplied by Congo River runoff. From September to March, SSS variability is driven by zonal advection, with a major contribution from Ekman wind‐driven currents. During spring‐summer, the observed SSS increase is likely explained by entrainment and vertical mixing. SSS budget and freshwater advection processes are discussed in the context of the shallow stratification induced by freshwater.

Plain Language Summary

The Gulf of Guinea receives large amount of freshwater from Congo and Niger rivers runoff and high precipitation. Since the freshwater is lighter than the seawater, the surface freshwater input is spread within large plumes that impact the upper layer vertical structure. The vertical stratification induced by the freshwater plume strongly impacts the air‐sea heat flux exchanges but also the vertical exchanges of nutrient and organic matter. The eastern Gulf of Guinea freshwater plumes remain poorly documented because of the scarcity of historical data in this region. This study, based on recent advance in remote sensing of the Sea Surface Salinity from ESA (European Space Agency) Soil Moisture and Ocean Salinity satellite mission, provides a robust characterization of seasonal variability of freshwater plumes in the eastern Gulf of Guinea by describing and quantifying their development, extent and dispersal patterns. The freshwater plumes are mainly supplied by rain (respectively river) input in the northern (respectively southern) part of this region. Their offshore seasonal evolution is mostly driven by surface currents and upward salty water fluxes. Surface wind‐driven currents are also found to play a major role for the freshwater plumes offshore extension.

Full Text
File Pages Size Access
Publisher's official version 57 5 MB Open access
Supporting Information S01 5 448 KB Open access
Movie S1 599 KB Open access
Top of the page

How to cite 

Houndegnonto Odilon, Kolodziejczyk Nicolas, Maes Christophe, Bourlès Bernard, Da Allada C. Y., Reul Nicolas (2021). Seasonal variability of freshwater plumes in the eastern Gulf of Guinea as inferred from satellite measurements. Journal Of Geophysical Research-oceans, 126(5), e2020JC017041 (27p.). Publisher's official version : https://doi.org/10.1029/2020JC017041 , Open Access version : https://archimer.ifremer.fr/doc/00690/80170/