Fig. 11.39 Coastal upwelling and wind-stress curl upwelling mechanisms. Upwelling
moves nutrients (dots) into the illuminated sea surface, promoting phytoplankton
growth (shading). Equatorward along-shore wind stress generates “Ekman” drift
seaward that is replaced by upwelling water from depth. That is “coastal” upwelling.
Wind-stress curl, i.e. a gradient in wind velocity (represented by progressively larger
arrowheads seaward), generates additional upward Ekman pumping (albeit at lower
vertical velocities) offshore. With substantial curl, the poleward undercurrent moves
more inshore and shallower, providing relatively more nutrients.
(^) (Modified from Albert et al. 2010.)