Why Is the Ocean Salty?

(Last Updated On: January 7, 2019)
Why Is the Ocean Salty?

We have a lot of water on Earth. In fact, about 70% of the Earth’s surface is covered by it. Most of this water can be found in our oceans, meaning that almost 97% of all water on Earth is salty. That’s a lot of salt! So where does it all come from? Why is the ocean salty in the first place?

Why Is the Ocean Salty?

It’s assumed that when the Earth first formed, the oceans probably weren’t as salty as they are today. As time moved forward and more rains fell on the planet, the oceans become saltier. This is because rain contains dissolved carbon dioxide from the air, which makes it slightly acidic. When the drops fall to earth, it physically erodes rocks and breaks them down chemically. As the water flows away from the surface and into rivers or toward the ocean, it transports minerals and salts as dissolved ions.

These ions are then carried into the ocean where they are used by some organisms, removing them from the water. Those that aren’t used by organisms begin to build up. The two most prominent ions that exist in the oceans include sodium and chloride. These make up more than 90% of all dissolved ions in the ocean. The salt concentration in seawater is 35 parts per thousand, which means that 3.5% of seawater’s weight comes from dissolved salts.

It is estimated that streams and rivers that flow from the U.S. carry 225 million tons of dissolved solids to the ocean, along with 513 million tons of suspended sediment. Worldwide, it’s estimated that rivers carry 4 billion tons of dissolved salt on an annual basis.

Other Sources of Salt

In addition to surface water and rivers/streams carrying salt to the oceans, it has been discovered that hydrothermal vents also contribute dissolved minerals into the ocean. These vents are created when seawater seeps into the rocks on the oceanic crust and then becomes hotter. As it passes through the rocks, the water breaks down the surface (much like rain does on land) and releases minerals. When the water exits the oceanic crust, which results in the development of a hydrothermal vent, the minerals come with it.

Another source of salt in the ocean comes from underwater volcano eruptions. This process is similar to the hydrothermal vent process and involves water getting hot and breaking down rocks to release the minerals.

Stories to Explain the Salt

In the past, when people asked why the ocean was salty, stories and lore were made up to explain the phenomenon. Back then, they didn’t have the scientific knowledge or understanding of the world as we do today, but some of the stories were incredibly creative, fun, and maybe a little gross.

One fun example comes from Australia. According to legend, the ocean is salty because an upset cockroach once decided to urinate everywhere, thus turning all freshwater into saltwater. Yuck!

Thankfully today we have a better understanding for why the oceans are salty. But even with advances in science, there is still much about this vast expanse of water that remains a mystery.

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