Where Is Ocean Salinity Highest? The Subtropical Zones

Maximum open-ocean salinity occurs in the subtropics (20°–30° N/S), where evaporation exceeds precipitation and river input is minimal. Surface salinity peaks at ~37 ppt (parts per thousand) in centers of subtropical gyres:

• North Atlantic (Sargasso Sea)
• South Atlantic
• North Pacific
• South Pacific
• Indian Ocean (Arabian Sea, subtropical gyre)

Enclosed seas exceed this: Red Sea (~41 ppt), Persian Gulf (~38–40 ppt), Mediterranean (~38 ppt). Polar and equatorial regions are fresher due to melting ice and heavy rain.