A realistic physical model of the Gibraltar Strait

Abstract. We present a large-scale laboratory model of the Strait of Gibraltar that reproduces realistic topography, tidal forcing, stratification, and rotation, enabling controlled investigation of key exchange processes linking the Mediterranean Sea and Atlantic Ocean. Velocity and density measurements confirm dynamic similarity with ocean observations. Analysis of the flow near Camarinal Sill shows that bottom boundary layers are the primary source of turbulent kinetic energy, exceeding contributions from shear at the interface between Atlantic and Mediterranean waters. The enhanced role of bottom-generated turbulence is linked to separation of the Mediterranean gravity current induced by an adverse pressure gradient during outflow, providing a new explanation for the well-documented detachment of the Mediterranean plume west of the sill. This detachment intensifies during spring tides, driving diluted waters farther into the Atlantic, while during neap tides bottom-generated and interfacial turbulence coincide, offering a consistent explanation for the high dissipation rates reported in field measurements. Overall, tidal forcing promotes full-depth mixing, with up to ~20 % density reduction west of CS and oscillatory ~20 % variations east, consistent with field data, and simultaneously introducing an important phase shift between velocity and density fields, with implications for parameterizing turbulent exchange and definition of the composite internal Froude number for reliable diagnose of hydraulic control. During spring tides, hydraulic control is intermittently lost during inflow and this loss propagates eastward, while additional control points arise west of the sill. Neap tides exhibit signatures of control which persist much longer during a tidal cycle as compared to spring tides, but does not propagate to the east when the tide reverses. Transport and energy budgets reveal strong longitudinal and transverse variability, highlighting the need for fully three-dimensional diagnostics. Volume transport, dominated by transverse topographic variability, exceeds salt transport by two orders of magnitude, confirming net Atlantic inflow. A phase-lagged internal bore release between the northern and southern transects is observed, consistent with field observations, and we show that it is independent of barotropic effects or Kelvin waves. These results demonstrate that high-fidelity laboratory modeling can capture the essential three-dimensional dynamics of energetic straits and provides a powerful complement to observational and numerical approaches.