Potential impact of stratospheric aerosol geoengineering on sea surface salinity in the eastern tropical Atlantic Ocean

Stratospheric aerosol geoengineering (SAG), which is based on the injection of sulfur dioxide into the stratosphere, is one of the methods proposed to mitigate the effects of global warming. In this study, we investigate the potential impact of SAG on sea surface salinity (SSS) in the Eastern Tropical Atlantic Ocean and the physical processes involved in SSS changes, using Geoengineering Large Ensemble (GLENS) simulations performed under the RCP8.5 scenario. Results reveal that, in the mean state, under global warming (RCP8.5), SSS decreases (relative to current climate) in the Northern Gulf of Guinea (NGG) around the Niger River region and in the Southern Gulf of Guinea (SGG) around the Congo River region, whereas, under SAG, SSS remains unchanged (relative to current climate) in both regions. At seasonal time scale, under RCP8.5 (relative to current climate), in the NGG region, SSS decreases all year round with strongly negative values of −0.6 PSU (practical salinity unity) in boreal winter (December/January), whereas under SAG, the decrease in SSS disappears and SSS turns slightly positive all year round (with SSS values below + 0.2 PSU). In the SGG region, under RCP8.5, SSS also shows a year-round decrease, as in NGG, with a maximum negative SSS value (−0.9 PSU) in May. Under SAG, from December to June, SSS increases with a maximum positive value (+0.4 PSU) in April and the rest of the year, SSS decreases with a strong negative value (−0.3 PSU) in September. Using SSS budget in the mixed-layer, the findings indicate that under RCP8.5 and SAG, in the NGG, changes in SSS are mainly caused by changes in precipitation and rivers runoffs, whereas in SGG, changes in rivers runoffs and vertical mixing are responsible for SSS changes.