Séminaire
The Eastern Boundary Upwelling Systems (EBUSs) are among the most productive marine ecosystems in the world, supporting some of the world's major fisheries (e.g., FAO 2009). They are characterized by the presence of equatorward wind, stratocumulus cloud deck, complex orography and coastline, and a high productivity driven by the wind-induced upwelling. Such a complex system is highly sensitive to climate change. For example, observations in the past decades show an acidification of the California upwelling. Additionally, climate scenarios suggest changes in the mean wind that could affect the ecosystems. Our most recent projects aim to simulate the past decades and the impact of climate change on the EBUSs, focusing first on the California upwelling. Within this framework, in this talk, we show the difficulties and highlight the key points that have to be carefully resolved in a coupled model to represent realistically those complex ocean-atmosphere-biogeochemical interactions. In particular, the shortwave radiation representation in the atmospheric model is assessed. We show the importance of taking into account a realistic droplet concentration that allows an accurate quantification of the cloud droplet auto-conversion into raindrops. Furthermore, we show how coastal wind shapes matter for the ocean and the biogeochemical response, by controlling the currents, upwelling, but also the mesoscale activity and then the eddy quenching of nutrients. We then assess their characteristics and show the wind drop-off is mainly driven by the orography. It is therefore necessary to have high resolution forcing to resolve the orography. Based on those results, we conclude by presenting some preliminary results of our long-term uncoupled and coupled simulations of the California upwelling.