Subinertial variability in the flow through the Strait of Gibraltar

[1] Current meter observations collected within Canary Azores Gibraltar Observations (CANIGO) project have been analyzed in order to study subinertial flows through the Strait of Gibraltar. Estimated net flow has been compared with hindcasts provided by Nivmar Prediction System-Hamburg Shelf Ocean Model (HAMSOM) circulation model forced by wind stress and atmospheric pressure applied to the North Atlantic Ocean and the Mediterranean Sea. The model was first run-forced by atmospheric pressure and then by atmospheric pressure and wind stress in order to assess the relative importance of each external agent on the subinertial flow. The main driving force is the atmospheric pressure over the Mediterranean Sea, although wind stress in the Atlantic side of the strait may contribute appreciably to subinertial net flow. Inflow variations account for 60% of the subinertial variability approximately. The interface depth correlates well with the net flow fluctuations, sinking or rising under positive (toward the Mediterranean) or negative fluctuations, respectively, with an average gain of around -60 m/Sv. These results have been interpreted in the scope of the hydraulic two-layer theory to conclude that the exchange is submaximal rather than maximal. Salinity on the interface increases (decreases) for positive (negative) net flow fluctuations. This is explained in terms of increased (decreased) recirculation of water from the passive Mediterranean layer driven by the velocity changes that atmospheric forcing induces in the active Atlantic layer. The contribution of the recirculated water to the fluctuations of the net flow is of secondary importance (around 5% on average), but the layer that recirculates may be thicker than 50 m, what could have important biological implications.