Rain and groundwater weather rock, rivers carry dissolved ions to the sea, and seafloor processes add more. Water continually leaves through evaporation, but most dissolved salts do not—so the ocean remains salty.
Three things to know
- Average salinity
- ~35‰
- About 35 grams of dissolved salts per kilogram of seawater, with regional variation.
- Main ions
- Na⁺ + Cl⁻
- Sodium and chloride dominate, but seawater contains many other dissolved ions.
- Long process
- Geologic time
- Inputs, mineral formation and biological cycling shape the modern balance.
From rock to river
Rainwater is slightly acidic. As it moves through soil and across rock, it dissolves small amounts of minerals. Rivers then transport those dissolved ions toward the ocean. The visible sediment in a river is only part of the delivery; clear water can still carry a substantial dissolved load.
The seafloor contributes too
Hydrothermal circulation and reactions between seawater and oceanic crust exchange chemicals at the seafloor. Volcanoes and underwater vents are therefore part of the salt story, but not the only source. The modern ocean reflects a long-running balance among inputs, biological uptake and minerals forming or being buried.
Why the ocean does not simply get saltier
Evaporation concentrates salts locally because water molecules enter the atmosphere while ions remain behind. Yet salts are also removed: organisms build shells, minerals precipitate, sea spray reaches land and altered seafloor crust stores ions. Ocean salinity is dynamic, not an endlessly rising pile.
What people usually ask
Is every part of the ocean equally salty?
No. Rain, river input, sea-ice formation, melting and evaporation produce strong regional and seasonal differences.
Why are rivers not salty?
Rivers contain dissolved ions, but their water is continually renewed and the concentration is far lower than in the ocean basin where salts accumulate.
Here’s where the answer came from
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