Mediterranean Sea Is ~8.6% Saltier Than Atlantic

Average salinity:

• Mediterranean Sea: 38‰ (parts per thousand).
• Atlantic Ocean: 35‰.

Difference: 3‰ absolute → 8.6% higher in the Mediterranean.

Why?

• High evaporation (subtropical latitude, enclosed basin).
• Limited Atlantic inflow (Strait of Gibraltar sill).
• Low river input relative to surface area.
• Net evaporation ≈ 0.5–1 m/yr; compensated by Atlantic inflow.

This salinity gradient drives the Mediterranean Outflow Water (dense, salty plume) into the Atlantic at depth—influencing global thermohaline circulation.