How does Atlantic Ocean water enter the Mediterranean Sea?

Atlantic Ocean water enters the Mediterranean Sea primarily as a continuous surface current flowing through the Strait of Gibraltar.1

This inflow is driven by the Mediterranean's hydrologic balance: the sea loses significantly more water through evaporation than it receives from rivers and precipitation. To compensate for this deficit, surface water from the Atlantic flows eastward into the Mediterranean, extending from the surface to a depth of approximately 70 to 80 metres (230 to 260 feet).12

This exchange is often described as the sea "breathing," as the incoming surface water is balanced by a deeper, westward-flowing countercurrent. Because the Mediterranean's surface water becomes more saline and dense due to intense evaporation, it sinks and exits back into the Atlantic as a subsurface current below the incoming Atlantic water. This constant exchange is essential, as it prevents the Mediterranean from becoming a shrinking, hypersaline basin.13