Return Flow

Return flow is the compensating current that closes a transport, balancing a surface flow with an opposing flow at depth (or vice versa) so that mass is conserved within a basin or section. Wind-driven Ekman transport at the surface is balanced by a geostrophic return beneath; the warm surface limb of the overturning circulation is balanced by the cold deep return carried by the Deep Western Boundary Current. The concept is built into Sverdrup balance and the closed gyre, where the broad interior Sverdrup transport is returned by a narrow western boundary current.