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Saltwater: How Oceans Get Their Flavor

Even the clearest ocean water contains complexities the eye can’t see. Uncover one of them with Groupon’s investigation of earth’s sodium-filled seas.

If you extracted all the salt from the ocean and spread it evenly across the surface of the planet, it would reach a height of 500 feet—44 feet higher than the world’s tallest rollercoaster. All that salt arrived there from a few sources. For millions of years, rainwater has slowly eroded rocks on land, releasing salt ions into streams and rivers that feed into the ocean. Hydrothermal vents and volcanic activity from below also release salt into the sea, and constant surface evaporation lifts water up but leaves salt behind.

Salt isn’t the only mineral in our oceans. At least 72 chemical elements have been identified in seawater, and oceans aren’t the only places this elemental soup exists. In fact, the same sources that give oceans their salinity also operate in what we think of as freshwater rivers and lakes, but because of lower salt concentrations in “fresh” water, human senses don’t register the compounds. Why are oceans so much saltier? The answer is rather simple: they’re huge (creating a large surface area for evaporation to do its work) and they’re constantly being replenished with rocks and other matter carried in from the rivers, most of which drain from lakes and springs into the sea. Once they get there, rocks have all the time in the world to be worn down by the ocean’s waves, contemplate writing their memoirs, and release their salts.

On average, the ocean’s salt content is about 3.5% of its total weight. This varies by location, however. For example, the landlocked Dead Sea’s constant evaporation makes its salinity extremely high, whereas melting ice dilutes polar seas. And slowly but surely, with each passing year, the forces of nature are making all seas, like the act of a child comedian, just a little saltier.