The overturning cell driven by alongshore wind and coastal upwelling off central California is examined using direct observations from four underwater gliders equipped with Acoustic Doppler Profilers. These show the onshore flow that compensates for offshore Ekman transport during the month of August 2006 to occur primarily just below the Ekman Layer so that the net offshore heat transport, and by inference the net vertical transport of nutrients, is much less than if this compensating flow occurred throughout the water column. Correlation of cross-shelf flow and wind stress is used to infer the profile of Ekman transport while glider-measured alongshore gradients of density determine the geostrophic cross-shelf flow, which is strongly surface-intensified. The sum of Ekman and geostrophic flows approximates the independently and directly measured cross-shelf flow profile. This underscores the importance of the alongshore pressure gradient in the overturning circulation and makes understanding it a high priority.
Davis, R. E.. 2010. "On the coastal-upwelling overturning cell." Journal of Marine Research 68, (3). https://elischolar.library.yale.edu/journal_of_marine_research/271