WHOI PO

Coastal upwelling revisited: how do nutrients make their way tothe surface?

Wind-driven upwelling ofcold, nutrient-rich water is a key feature near the eastern boundaries of majorocean basins, with significant implications for the local physical environmentand marine ecosystems. For a long time, wind-driven coastal upwelling has beenexamined within a simplified two-dimensional framework where the upwellingcirculation is considered as a passive response to the surface offshore Ekmantransport. As a result, a systematic understanding of the factors governing thespatial patterns of coastal upwelling and the pathways of nutrient transportremains elusive. Here, we delve into the physics of three-dimensionalwind-driven coastal upwelling over the continental shelf and identify twoleading-order pathways for nutrient upwelling: the residual circulation andeddy stirring associated with baroclinic instability. In particular, wedemonstrate the factors that determine the spatial structures of the residualcirculation and highlight the importance of eddy stirring, which works in synergywith the residual circulation in transporting nutrients in the coastal ocean.The results may help to improve our understanding of coastal upwelling systemsand yield a more physical representation of coastal upwelling incoarse-resolution numerical models.