Why is the Ocean Salty?

Ah...the beach. We recently returned from a trip to the coast of North Carolina where we enjoyed four days of sun, surf, and SALT. I have always been amazed by this unique property of ocean water. You can smell the salt before you step foot on the beach. After a refreshing dip in the ocean you are left with a grainy texture all over as you dry off in the sun. By the time you leave the beach the salt is on your skin, in your hair, and there is even a fine layer over your sunglasses. Where does all of this salt come from?

When I was young I heard an old folk tale about a magic salt mill at the bottom of the ocean. I don’t think this is the answer.

This is a common question but a good one. Rain isn’t salty, rivers and streams that dump out into the ocean aren’t salty either. So why is the ocean salty?

The answer to this question starts with the formation of the earth. Gases containing salt were released from below the earth’s surface into the ocean water. Ever since then, salt is continually dumped into the ocean from rivers. Wait, rivers aren’t salty, are they? Yes, rivers do in fact contain a small amount of salt, just not enough to taste. The salt comes from eroding rock, soil and other organic sources that the river picks up on its journey to the ocean. All the rivers of the world dump into the ocean, the river water evaporates, and the salt is left behind. Here is a diagram illustrating this concept:

http://www.palomar.edu/oceanography/salty_ocean.htm

How much salt is in the ocean? One cubic foot of ocean water will yield over two pounds of salt. All of the ocean salt could cover the entire earth’s surface, 40 stories high!

Ok, I understand now why the ocean is so salty. Salt has been washed into the ocean since the formation of earth. Since salt doesn’t evaporate, will the ocean eventually fill up with salt? Some scientists claim that the ocean’s salt content is higher now than millions of years ago. I imagine there would need to be a major shift in the hydrologic cycle before the amount of salt would exceed the amount of water in the ocean.

Some areas of the earth have higher salt concentrations than others. The Arctic is less salty with the presence of melting glaciers, and the Persian Gulf has the saltiest water due to higher rates of evaporation.

Salt is present all over the earth, but thanks to the rivers, salt is washed into the ocean where it is left for us to enjoy. The salty air, the gritty film on your sunglasses, even the mouthful of salt water you get when surprised by a wave, all adds up to a great vacation.

Experiment:
You can show your children how salt is left behind in the ocean by doing the simple evaporation experiment described at the bottom of the page at the following link:
http://wondertime.go.com/learning/article/0806-why-the-ocean-is-salty.html 

Sources:
http://www.palomar.edu/oceanography/salty_ocean.htm
http://wondertime.go.com/learning/article/0806-why-the-ocean-is-salty.html