Why is the Ocean Salty?

Posted on in Todd Talks by Todd Johnson

I am a father of two cute and curious little girls. Like all parents, I get a lot of questions. Some are head scratchers that make me do a little research and force me to freshen up on things I learned (or was supposed to learn) back in my school days. Others are just completely out of left field and hard or impossible to answer. I'm thinking I would like to start a "Why is?" or "What is?" series of entries to cover these questions. I'm constantly reminded by my girls how much I forget. I invite those of you reading this to reach out with some of the things your kids have asked you. I think it would be fun to see how similar and curious our children are, and how much we all forget that we (probably) learned at some point. I can't promise that I'm going to research all the questions and provide all the answers, but I just might look into some of them. But I digress. Today the question is: "Why is the ocean salty?"

As it turns out, the answer to that question makes a lot of sense. Rain falls on land and eventually finds its way to the sea by way of creeks, streams, and rivers. That rain is slightly acidic, and as it falls on the dirt and rock of the land, it slowly erodes the ground and washes the particles away. Rocks and soil are full of minerals, and one of those minerals is sodium. The sodium and other minerals are then washed into rivers that eventually make their way to the ocean. Many of these minerals are used by sea life and thus removed from the water. Others are not used and increase in concentration over time.

While this is where most of the salt in the ocean comes from, it is not the only source. A second major source is actually in the ocean already in the form of vents in the sea floor. Seawater enters these cracks and is heated by magma in the earth. It's then released back into the ocean with a higher concentration of minerals due to chemical reactions that happened when the water was heated with the surrounding rocks.

So, if rivers carry salt to the ocean, why aren't lakes salty? Lakes are fed by rivers too! Well, lakes are also drained by rivers. This activity carries away much of the small amount of dissolved minerals. The ocean is only "drained" by evaporation, which does not take minerals with it. If a lake has no outflow, it becomes salty, and usually more so than the ocean. The Dead Sea in Jordan and the Great Salt Lake in Utah are great examples of this.

Now you can provide a good answer to your children if they ask this question. No kids? Well then, you're all set for trivia night!