Impact of stratospheric aerosol injection on ocean surface circulation in the Gulf of Guinea

Stratospheric aerosol injection (SAI) has been proposed as a climate intervention strategy to mitigate global warming by reflecting part of incoming solar radiation. Using simulations from the geoengineering large ensemble under the high-emissions RCP8.5 scenario, this study investigates the projected impacts of SAI on the seasonal variability of ocean surface currents in the Gulf of Guinea (GG) and their underlying mechanisms. We analyze changes over 2050–2069 relative to a 2010–2029 baseline, focusing on the guinea current (GC) and the south equatorial current (SEC). The model reproduces the observed large-scale circulation, providing confidence in the projections. Decomposition of the total current into geostrophic and Ekman components reveals that projected changes are primarily driven by geostrophic processes linked to sea surface height gradients. Under RCP8.5, the GC intensifies in boreal winter, while the SEC shows a dipole response, with slight acceleration near the equator and weakening further south. In boreal summer, the GC weakens along its northern branch but slightly strengthens in its core, whereas the SEC generally weakens. Under SAI, similar spatial patterns persist but with reduced amplitudes. A key feature of the SAI response is the mismatch between reconstructed and simulated zonal currents, suggesting enhanced ageostrophic and nonlinear processes. Overall, while SAI dampens warming-induced circulation changes, it introduces additional dynamical complexity, highlighting the dominant role of ocean dynamics in the GG.