STEADY 2-LAYER EXCHANGE THROUGH THE STRAIT OF GIBRALTAR

Recent progress in steady hydraulic control modeling of the two-layer flow through the Strait of Gibraltar is reviewed. An application of the model is made to the specific physical configuration of the Strait using the most recent bathymetry. The maximal exchange solution resulting from the model must satisfy mass and salt conversation relations for the Mediterranean Basin. Hence, it is not possible to specify arbitrarily the density difference between the inflowing and outflowing layers, and the proper reservoir condition is a specification of the net evaporation over the Mediterranean Basin. For a specified evaporation, both the magnitude of the maximum two-layer exchange and the density or salinity difference between the inflowing Atlantic water and outflowing Mediterranean water can be determined from the combination of the hydraulic control model and mass and salt conservation statements. For net evaporation values between 50 and 70 cm y-1, the predicted inflow, outflow and salinity difference are in reasonable agreement with recent observations. In particular, for a net evaporation of 60 cm y-1, the steady hydraulic control model yields a predicted inflow of 0.92 x 10(6) m3 s-1, an outflow of 0.88 x 10(6) m3 s-1 and a salinity difference of 2.0 parts per thousand. For comparison, recent observations exhibit an inflow of 0.95 x 10(6) m3 s-1, an outflow of 0.79 x 10(6) m3 s-1 and an effective salinity difference of 2.1 parts per thousand.