Why the Mediterranean needs water exchange
On average, the Mediterranean loses more water through evaporation than it receives from precipitation and rivers. Atlantic inflow compensates the deficit. Saltier, denser Mediterranean water exits at depth towards the Atlantic.
Two layers that are not perfect pipes
The most useful picture is a two-layer system: eastward Atlantic flow near the surface and westward Mediterranean flow below. The interface moves, tides are strong and water masses mix.
The role of Camarinal Sill
Camarinal Sill is a submarine high that hydraulically controls part of the exchange. Currents accelerate, creating internal waves, hydraulic jumps and turbulence that transform the Mediterranean outflow.
Tides, mixing and variability
Instantaneous flow can differ greatly from the mean. Semidiurnal tides modulate currents and mixing, so a few hours of observations cannot represent the complete system.
Why it matters beyond the Strait
Mediterranean outflow contributes to intermediate waters in the northeastern Atlantic. The connection also controls Mediterranean water level and salinity over long timescales, making the Strait a natural laboratory for hydraulics and ocean circulation.
Connection with fixed-link studies
Oceanography alone does not decide tunnel feasibility, but currents, sediment dynamics, seabed conditions and research campaigns must be understood before any infrastructure is designed and built.