Modelling coastal upwelling off NW Iberian Peninsula: New insights on the fate of phytoplankton blooms

Abstract

The northwestern coast of the Iberian Peninsula is a region characterized by pronounced hydrologic and biogeochemical activity, resulting in important fish and shellfish resources whose exploitation has a strong local socioeconomic impact. This high biological diversity is strongly dependent on coastal upwelling induced by favourable winds, which presents seasonal variability. This motivates the present study, which aims to understand the relation between local circulation, hydrography and Chl-a concentration under summer upwelling events of different intensities and clarify their effects in the region. To achieve this purpose, a coupled physical-biological model was developed and validated for the northwestern coast of the Iberian Peninsula, based on the use of MOHID modelling system and the application of a nested domains methodology. Comparison of predictions with observations demonstrated the model's accuracy in reproducing the physical and biogeochemical properties of the study region, both at the surface and along the water column. The study of different summer upwelling events shows that the local phytoplankton patterns are dependent on the characteristics of the event. Results show that under high upwelling favourable winds, a surface southwestward flow and an equatorward flow through the water column develop near the coast, inducing offshore advection of nutrient and phytoplankton-rich waters. Otherwise, under light upwelling favourable winds, surface currents are weak, a poleward flow develops, and phytoplankton is retained near the coast.