"Hydrometeorology and Monitoring Center" NOSC has published an article about why ocean water is salty and rivers are mostly fresh.
Rainwater, which is weakly acidic under natural conditions, as a result of interaction with atmospheric carbon dioxide, passing through rocks and soil layers, gradually dissolves various minerals and salts. These dissolved substances are transported by rivers to lakes, seas and oceans.
River water is constantly refreshed by precipitation, groundwater, and runoff, keeping dissolved salts relatively low, and most rivers are freshwater.
The situation in the oceans is different. water evaporates constantly under the influence of the sun, but the dissolved salts do not evaporate and remain in the water. Over millions of years, they gradually accumulated to form the current salinity of ocean water, which averages about 35‰ (35 grams of salt per liter of water).
Ocean water is dominated by sodium chloride (table salt), but it also contains compounds of magnesium, calcium, potassium and other elements.
