Potential changes over a warmer climate in the Benguela Upwelling System within an Oxygen Minimum Zone

The Benguela upwelling system (BUS) presents one of the highest primary productions of all Eastern Boundary Upwelling Systems with an Oxygen Minimum Zone (OMZ) in its northern part. We investigate the impact of different drivers on production, biomass and acidification in the BUS under future potential climate change (scenario A1B2, 2080-2100: A1B_(2080-2100)) compared to present period (PD_(1980-2000)). A 3-D regional high resolution coupled physical-biogeochemical model (already validated for the BUS) was forced by global climate simulations with downscaled winds from the IPSL model projection. The results show that in the BUS this forcing corresponds to an mean SST increase of 1.4°C over the whole domain and is associated with a decrease of alongshore winds magnitude (-10% in its northern part) and of oxygen concentrations (-20-30 mmolO₂.m^-3 in its northern part). These climate drivers influence the ecosystem of the BUS with a subsequent a decrease of the surface pH (-0.24) and decrease of primary production (-0.12; fractional change = (A1B_(2080-2100)/PD_(1980-2000))-1 (-1 to 0: decrease, positive values: increase)), phytoplankton (-0.148) and zooplankton (-0.126) biomasses over the whole domain. However an unexpected ecological niche with increased production and plankton biomass could develop in the northern part of the BUS and along the coast, associated with the increase of temperature, stratification and decrease of the winds. The coupled processes are analyzed in order to understand this ecological niche.