Camarinal Sill

The Camarinal Sill is the sill separating the Mediterranean Sea and the Atlantic Ocean. This threshold is the shallowest seafloor pass between the Iberian Peninsula and Africa. It is located near the Strait of Gibraltar and the Espartel Sill, at 35°56′N 5°45′W, at an elevation of −280 m.

Its formation is linked to the termination of the Messinian salinity crisis, when the Mediterranean was abruptly refilled through the Gibraltar Strait, excavating the 900-metre-deep gorge that lies underneath the water. A competing hypothesis suggests that both the gorge and the Camarinal Sill are the result of fluvial erosion during the desiccation of the Mediterranean (Messinian salinity crisis).

Marine waters must climb to that depth when flowing between both ocean domains. So did also submarines during World War II, using the upper inflow current and the lower outflow current to go in and out from the Mediterranean Sea without using their engines, to avoid being noticed from the surface.