All Oceans Are Salt Water — Here's Why

Yes. All five global oceans (Pacific, Atlantic, Indian, Southern, Arctic) are salt water. Average salinity: 35 PSU (35 g salts/kg seawater).

Sources of Salt

• Continental Weathering: Rain (weak carbonic acid) erodes rocks → ions (Na⁺, Cl⁻, Mg²⁺, SO₄²⁻, Ca²⁺, K⁺, HCO₃⁻) carried by rivers to sea. #1 source.
• Hydrothermal Vents: Seawater circulates through crust, leaches metals/minerals, exits superheated. Adds Mg, Fe, Mn, etc.
• Submarine Volcanism: Direct eruption inputs.
• Atmospheric Deposition: Dust, volcanic ash, sea spray recycle.

Why Not Fresh?

• Rivers bring fresh water + dissolved salts.
• Evaporation removes pure H₂O → salts concentrate.
• No outflow (oceans are terminal basins) → salts accumulate over geologic time.
• Steady state: input ≈ removal (sedimentation, hydrothermal, subduction).

Salinity Range

• Open ocean: 33–37 PSU.
• High evaporation / low input: Red Sea (41 PSU), Persian Gulf (40+), Mediterranean (38–39).
• High input / ice melt: Baltic (2–10), Arctic coastal (20–30), near river mouths (<5).

No ocean is fresh. "Freshwater seas" (Caspian, Aral, Dead Sea) are endorheic lakes — no ocean connection.