Why Is Seawater Salty?

Full transcript

Have you ever swum in the ocean and accidentally swallowed a mouthful of water? That unmistakable salty taste has a fascinating scientific explanation. It all begins on land, where rainwater slowly seeps into the ground and flows across rocks, dissolving tiny amounts of minerals and salts along the way. These rivers and streams carry dissolved minerals, especially sodium and chloride ions, on a long journey that eventually leads them straight to the ocean. Once in the ocean, the water evaporates into the atmosphere as clouds, but the salt is too heavy to evaporate, so it stays behind and accumulates. The ocean floor also contributes to the saltiness, as underwater volcanoes and hydrothermal vents release additional minerals directly into the deep seawater. Over billions of years, this cycle repeats endlessly — rain falls, dissolves minerals, rivers flow to the sea, water evaporates, and the salt concentration keeps building up. Today, the ocean is about 3.5 percent salt by weight, and without this constant geological recycling process, our seas would be as fresh as a mountain stream.