Impact of stratospheric geoengineering on ocean dynamics in the Eastern Equitorial Atlantic

The challenges of adaptation to global warming have motivated studies of several possible mitigation techniques,
including that of solar geoengineering or stratospheric SRM, which involves the injection of sulfur aerosols into the
stratosphere to reduce the solar radiation reaching the Earth's surface to cool the planet. The main objective of this
thesis is to investigate the impact of stratrospheric SRM on ocean dynamics in the Eastern Equatorial Atlantic using
simulations from the Geoengineering Large Ensemble (GLENS) project. Firstly, analyses reveal that in the Gulf of
Guinea (GG), under global warming (RCP8.5), throughout the year, there is an intensification (relative to current
climate) of the Guinea Current (GC) while the South Equatorial Current (SEC) weakens, and these changes are
mainly controlled by the modification in the geostrophic component of the zonal surface current. However, under
stratrospheric SRM, in the GG, all the year, on the one hand, contrary to RCP8.5, the GC above 3°N slows down and
the SEC below 8°S accelerates, while on the other hand, as under RCP8.5, under stratrospheric SRM, the GC between
2°N and 3°N intensifies while the northern and equatorial branches of the SEC slow down. Unlike in RCP8.5, these
current modifications are essentially linked to changes in the Ekman component of the current, with a non-negligible
contribution from its geostrophic component. Secondly, results show that throughout the year, under RCP8.5, there
is a warming (relative to current climate) of the sea surface temperature (SST) in the Equatorial Atlantic Cold Tongue
region, and the use of the SST budget highlights that the weakening of vertical mixing at the base of the mixed layer
is largely responsible for the SST increase. Under stratrospheric SRM, contrary to RCP8.5, SST decreases all the
year, and these SST changes are mainly explained by changes in westerly winds in the equatorial Atlantic basin.
Finally, the last part of this thesis focused on the impact of stratospheric SRM on the SSS in the Equatorial Atlantic
Cold Tongue region. Analyses revealed that under both RCP8.5 and stratospheric SRM, there is a slight increase
(relative to current climate) in SSS. However, whereas under RCP8.5, these SSS changes are due to a slight increase
in evaporation and a strong decrease in precipitation, with a non-negligible oceanic contribution, under stratospheric
SRM, these changes in SSS are mainly linked to a reduction in precipitation.