Preprints
https://doi.org/10.5194/egusphere-2024-3320
https://doi.org/10.5194/egusphere-2024-3320
29 Oct 2024
 | 29 Oct 2024
Status: this preprint is open for discussion.

River discharge impacts coastal Southeastern Tropical Atlantic sea surface temperature and circulation: a model-based analysis

Léo C. Aroucha, Joke F. Lübbecke, Peter Brandt, Franziska U. Schwarzkopf, and Arne Biastoch

Abstract. The Southeastern Tropical Atlantic (SETA) coastal region sustains highly productive fisheries and marine ecosystems, thus having immeasurable socio-economic importance for West African countries. It is characterized by high sea surface temperature (SST) variability and freshwater input from land mainly due to Congo River discharge. In this study, using high-resolution ocean model sensitivity experiments, we show that the presence of low salinity waters from the river discharge increases the mean state SST in the SETA coastal fringe by about 0.26 °C on average and by up to 0.9 °C from south of the Congo River to the Angola-Benguela front (ABF). North of the Congo River up to about 4° S, this input significantly reduces the mean state SST by more than 1 °C. We demonstrate that the impact of river discharge on SST is associated with a halosteric effect, which modifies the sea surface height gradient and alters geostrophic currents, producing a southward (northward) coastal geostrophic flow, with an onshore (offshore) geostrophic component to the south (north) of the Congo River. Hence, advective warming (cooling) and downwelling (upwelling) are generated south (north) of the river mouth. Furthermore, the southward advection generated by the low salinity waters pushes the ABF further south. These results draw attention to the freshwater impact on SSTs and ocean surface dynamics, especially in the projected climate change scenario of continuously increasing land to ocean discharge.

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Léo C. Aroucha, Joke F. Lübbecke, Peter Brandt, Franziska U. Schwarzkopf, and Arne Biastoch

Status: open (until 24 Dec 2024)

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Léo C. Aroucha, Joke F. Lübbecke, Peter Brandt, Franziska U. Schwarzkopf, and Arne Biastoch

Data sets

Supplementary Data to: River discharge impacts coastal Southeastern Tropical Atlantic sea surface temperature and circulation: a model-based analysis Léo C. Aroucha and Franziska U. Schwarzkopf https://hdl.handle.net/20.500.12085/2b927bcd-afab-4bc6-ba97-634d09435daa

Model code and software

Supplementary Data to: River discharge impacts coastal Southeastern Tropical Atlantic sea surface temperature and circulation: a model-based analysis Léo C. Aroucha and Franziska U. Schwarzkopf https://hdl.handle.net/20.500.12085/2b927bcd-afab-4bc6-ba97-634d09435daa

Léo C. Aroucha, Joke F. Lübbecke, Peter Brandt, Franziska U. Schwarzkopf, and Arne Biastoch

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Short summary
The West African coastal region sustains highly productive fisheries and marine ecosystems influenced by sea surface temperature. We use oceanic models to show that the freshwater input from land to ocean strengthens a surface northward (southward) coastal current north (south) of the Congo river mouth, promoting a transfer of cooler (warmer) waters to north (south) of the Congo discharge location. We highlight the significant impact of river discharge on ocean temperatures and circulation.