Why Is the Ocean Salty?

If you've ever accidentally swallowed seawater at the beach, you know just how salty the ocean is. But why? Let’s dive into it!

Where Does the Salt Come From?

The salt in the ocean comes primarily from rocks on land. Rain might seem pure, but it's actually slightly acidic because it absorbs carbon dioxide from the atmosphere, forming a weak carbonic acid. When this rainwater falls on land, it flows over rocks and soil, slowly dissolving minerals. These minerals include various salts, with sodium chloride (common table salt) being the most abundant.

As rainwater washes over rocks, it picks up tiny amounts of dissolved minerals and carries them into streams and rivers. These rivers then flow into the ocean. While each river might only carry a small amount of salt, but with thousands of rivers constantly flowing into the ocean for millions of years, the salt accumulates.

Another significant source of ocean salt comes from hydrothermal vents on the ocean floor. These underwater volcanic openings release minerals from deep within Earth's crust directly into the seawater. 

Why Doesn't the Ocean Keep Getting Saltier?

This is because some salt gets removed when seawater evaporates in shallow areas and salt deposits form. These deposits can eventually become buried and turn into rock salt formations on land. Salt is also removed by marine organisms that use minerals to build shells and skeletons. When these creatures die, their shells sink to the ocean floor and become part of the sediment, locking away the minerals they contain. Additionally, salt gets trapped in clay minerals and sediments on the ocean floor through chemical reactions.

Why aren't Rivers Salty then?

It’s because rivers are constantly moving. Fresh rainwater is always diluting them, and the water flows quickly enough that salt doesn't have time to accumulate in high concentrations. So you typically can’t taste the salt in river water.

How Salty Is the Ocean?

Ocean water is about 3.5% salt by weight. The most common salt in seawater is sodium chloride (table salt), but seawater also contains magnesium, calcium, potassium, and many other minerals. This mix of minerals is why ocean water tastes different from the salt you sprinkle on your food.