Influence of Stratospheric Geoengineering on the Salinity Barrier Layer Seasonal Cycle in the Northeastern Gulf of Guinea

Barrier layer (BL), by reinforcing ocean stratification, can maintain sea surface waters warming and limit nutrients supply into the euphotic layer, which is important to marine life. This study investigates the influence of stratospheric aerosol geoengineering (SAG) on the seasonal variability of the BL in the northeastern Gulf of Guinea (NEGG) and its causes based on data from the Geoengineering Large Ensemble project simulated under a high anthropogenic emission scenario and on observations. Results show that the model reproduces well the BL pattern according to observations in the northern Gulf of Guinea. BL is thicker in the NEGG, especially during boreal autumn, with barrier layer thickness (BLT) reaching a maximum value of 19 m in October. Under global warming compared to the current climate, the BLT increases slightly at the beginning of the year and strongly in boreal autumn by 14% with a maximum of + 4.5 m reached in November. The largest increase in BLT occurs in the NEGG, but the region of BL thickening also expands spatially toward the western Gulf of Guinea. The increase of BLT during boreal autumn is related to a 14% increase in river runoff and precipitation, with river runoff increasing by 17% and precipitation by 8%. Under SAG compared to the current climate, the BLT increases by 2% during boreal autumn in NEGG. This increase in BLT is relatively minor compared to global warming and is explained partly by a decrease in river runoff and precipitation of − 7%. Ocean dynamic processes through zonal advection and vertical mixing contribute to the little increase of BLT.