Impacts of stratospheric aerosol injection on the upwelling systems along the eastern boundaries of the southern tropical Atlantic Ocean

Résumé

Abstract The Angola–Benguela upwelling system (ABUS), a vital marine ecosystem in the southeast Atlantic, supports rich fisheries and provides food and economic security for coastal populations. While several studies have shown that global warming is altering sea surface temperature variability and upwelling dynamics across its subsystems, there is a dearth of knowledge about the extent to which human intervention, like stratospheric aerosol injection (SAI), could mitigate the influence of global warming on ABUS. This study investigates projected physical changes in the ABUS under a mid-range emission scenario (SSP2-4.5) and evaluates the potential of SAI to mitigate these impacts. We focus on the three major upwelling subsystems: the south Benguela (sBUS), north Benguela (nBUS) and Angola upwelling systems (AUS). Using earth system climate model simulations, we analyse changes in two key physical parameters critical for ecosystem development: ocean temperature and upward motion. Under the SSP2-4.5 scenario, the southeast tropical Atlantic, including upwelling regions, is projected to warm by up to 1.4 °C. This warming is primarily driven by enhanced downward LWR and modulated by cloud radiative effects and ocean circulation. Despite this warming, the upwelling dynamics remain largely unaffected during the main upwelling seasons: December to February (DJF) in sBUS and June to August (JJA) in nBUS and AUS. In contrast, during the secondary upwelling seasons (JJA in the sBUS and DJF in the nBUS and AUS), the upward motion intensifies by ∼30% in the AUS and by 10%–20% in the sBUS, while a weakening is projected in the nBUS. Under the SAI scenario, most of the climate change (CC)-induced warming is offset, with up to 90% of the temperature increase mitigated, particularly within the upper 150 m. The thermocline shoals by up to 80% of the CC-induced deepening. Additionally, the SAI scenario reverses up to 90% the CC-driven intensification of the upward motion during secondary upwelling seasons across all three upwelling subsystems. However, SAI fails to restore large-scale offshore ocean circulation in the broader ABUS region. Overall, these results highlight the spatially uneven effectiveness of SAI in moderating regional ocean-climate feedback within the ABUS.

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