Downscaling biogeochemistry in the Benguela eastern boundary current

•Regional downscaling of ocean–atmosphere global climate model improves upwelling solution.•Reliable wind forcing is a necessary condition of successful oceanic downscaling.•Regional downscaling reduces local biases in biogeochemical properties of water masses.•Downscaling modifies the structuring of the first trophic levels of the marine food web.•Potential biogeochemical upscaling effects are highlighted by this regional downscaling.