Eddy Compensation in Wind-Driven Subtropical Gyres
The existence of eddy compensation in the Southern Ocean, in which an eddy induced overturning circulation largely compensates the Ekman driven overturning circulation, is widely accepted.We use output from an idealised eddy-resolving model to show that eddy compensation also occurs within wind-driven gyres and explore the impacts of this on the nutrient budget of the gyre. By analysing vertical potential vorticity fluxes, Lagrangian particle trajectories, and depth-density stream functions we show that Ekman induced downwelling is opposed and largely compensated by eddy induced upwelling. The implications of this result for biological productivity are explored by the inclusion of a simple nutrient in our model. Our results may explain the unexpectedly high levels of biological productivity observed in subtropical gyres despite the presence of large-scale Ekman-induced downwelling.