Science Facts

Why Is The Sea Water Salty? – Causes & Facts

Sea Salt

There are five oceans on earth. The Pacific Ocean is the biggest then Atlantic, Indian, Southern, and Arctic oceans. Some oceans are saltier than others, but usually, around 3.5 percent of ocean water is salt. The seafloor has vast amounts of minerals that are constantly being switched world and stirred up by the natural motion of the ocean. This causes tiny amounts of minerals called salts to break away from the seafloor and dissolve into the ocean water, making it salty.

On average, oceans consist of about 3.5 percent salt that equates to 50 million billion tons of salt in our seas. If you were to pile all of that salt onto the Earth’s land, it would create a layer 152 meters high.

Why is the seawater salty?

Some salts dissolved into the ocean from rock and sediment on the seafloor. Other salts escaped from volcanic vents beneath the waves, but most come from the land around us. Seawater is salty for 2 major reasons or factors.

  • By hydrothermal fluids.
  • By natural water resources.

By hydrothermal fluids

A major factor responsible for turning the oceanic water salty is hydrothermal fluids. It comes from winds on the seafloor. The seafloor is heated by magma from the earth’s core. This heat causes a chain of chemical reactions, and the water tends to lose oxygen, magnesium, and sulfates. Then it picks up metals such as iron, zinc, and copper from surrounding rocks.

The heated water is released through winds on the seafloor carrying the other metals with it. As a result, the ocean water gets saltier. Two of the most common minerals in seawater are chloride and sodium. They make up around 85 percent of all dissolved minerals in the ocean and make water saltier.

Chemical formula of salt: Acid + Base = Slat + Water, HCl(aq) + Na(OH)(aq) → Water + NaCl(aq), Na + Cl → NaCl

The chemistry of the world’s oceans is not equal to the chemistry of the rivers coming into it. A black smoker is microcrystals of minerals under the sea surface. Scientists found the black smokers that the entire volume of the world’s oceans goes inside the earth and out every six to eight million years. It’s taking some of the chemicals it gets from rivers, trading them for new chemicals like sodium chloride, calcium chloride, etc. This occurs all along the mid-ocean ridge that stretches around the planet like the seam of a baseball. Also, tens of thousands of magma chambers are down there, and the waters get into them.

By natural water resources

One fantastic thing is why the oceans are salty, but other waters like lakes and rivers aren’t salty at all. The water in lakes and rivers is fresh. In fact, when scientists are studying any of the water that they find on Earth, that’s one of the first things they do. They figure out if it is saltwater, like the ocean, or freshwater, like lakes and rivers? So why is the water in the ocean different from the water in lakes and rivers?

Scientists have developed special tools and equipment that they can use to measure very small amounts of things. And they discovered something really surprising. Even though in lakes and rivers water have a small amount of salt. But the water in lakes and rivers is a little bit salty. In fact, every place they look, it doesn’t matter if it’s the tiniest pond or stream. There’s still a little bit of salt in the water. There’s one exception, and that’s this: rainwater.

When it rains, that water falling from the sky has no salt in it at all. Even rain that falls on the ocean, there are zero salts in the raindrops. So rainwater is 100% entirely freshwater. Scientists discovered that once rainwater hits the ground, like when it starts to form puddles or when it trickles down into streams and rivers, that’s when it starts to become a little bit salty. So then, there must be something about the ground itself that makes the water in lakes and rivers just a tiny bit salty.

  • When the rain forms and pose through the air, it collects carbon dioxide from the atmosphere on its way. Then it turns the freshwater slightly acidic. Once this acidic water meets the land surface, it erodes the rocks and picks up small amounts of salt.

According to the US Geological Survey, the water molecule is polar, and the oxygen atom hogs the electrons. So it’s more negatively charged on one side and more positively charged by the hydrogen atoms. When salts are in the water, they break apart because the ionic attraction is the only thing holding them in their crystalline shape.

Geologists can figure out that most rocks and soil contain tiny amounts of salt. When rainwater lands on the ground, it absorbs some of that salt. As that rainwater trickles into lakes and rivers, it carries the salt with it. This is why the water in lakes and rivers has a little tiny amount of salt. But rain itself, when it’s falling, has no salt since it hasn’t come in contact with the ground yet.

Rainwater dissolves minerals and salts from the rocks on dry land. So as rainwater makes its way downriver, it collects more and more salts. The amount of salt in this freshwater is still tiny, about 220 times less than seawater. This salt is then deposited into the sea when the river has run its course. Since rivers and lakes are located on the continents or land, higher up than the ocean. The water in the rivers and lakes usually flows down into the ocean. Even though river and lake water only carries a tiny amount of salt. That water’s been flowing for years and years down into the ocean. All that salt that it does carry keeps getting added to the ocean over and over, where it probably never leaves.

Importantly, the salt becomes more concentrated in the sea because the sun’s heat distills the water from the ocean surface, leaving the salt client. Across the globe, 4 billion tons of salt are deposited into our oceans every year from rivers. So surely seas must be getting saltier certainly the oceans have brought a lot saltier since their ancient beginnings. As much salt is being deposited on the ocean floor, it is coming from the rivers. So it’s reached a general equilibrium.

However, there are differences in salinity across the globe towards the poles. Seawater is diluted by melting ice caps and heavy precipitation. Meanwhile, in areas bordering the equator where its hot evaporation rates exceed the amount of rainfall. So water here is much saltier. And there is evidence to suggest that these differences are increasing.

As sea temperatures rise, parts of the Atlantic have already shown great evaporation rates and, with it, a rise in salinity levels. This may not seem important, but the more salt in the ocean, the greater its density and slower circulation. It means important marine nutrients won’t get distributed around the globe but interestingly. It’s not just sodium chloride that is gathered by rainfall and freshwater systems. Rivers carry and deposit more calcium than chloride.

So why is it our seas aren’t full of calcium? It’s because living organisms like mollusks, crustaceans, and coral use vast amounts of calcium in various forms to build their body structure. Without this influx of salt and minerals from rivers and streams, life would undoubtedly differ in oceans.

Properties of salt water

The salt in the oceans is 90% the same chemical makeup as table salt, NaCl. Sodium Chloride isn’t the only kind of salt there is. There are many varieties. That is because salt is just a compound held together by an ionic bond. What happens is an atom steals an electron from another and becomes negatively charged or an anion?

It’s attracted to the positive cation and the two atoms bond. So a lot of different chemicals can come together and make salts. The ocean salt is also made of magnesium, calcium, potassium, and a polyatomic anion produced of sulfur and 4 oxygens called sulfate.

Salt water facts

1. The salt content of seawater is referred to as its salinity. On average, 100 grams of seawater contains 3.5 grams of dissolved salts. It means that the salinity is 3.5%. The saltiness of water in the open ocean is nearly constant, lying within a narrow range between 3.3 and 3.7 percent.

2. The Dead Sea or the Great Salt Lake, and they have no outlets. The salt slowly builds up in the water, with nowhere to make the waterway saltier than the ocean. The Great Salt Lake can get up to 27% salt, and the Dead Sea can be close to 34%. That’s about 10 times saltier than the ocean. It means no aquatic life can survive there except for bacteria.

3. Humans and animals on the surface can not drink salt water. It can be drinkable by the desalination process.

Why can’t you drink saltwater?

The concentration of the salt is so high in seawater. It contains roughly 3.5 percent salt, and your kidneys will need to dilute the salt to process it. So they would need to use up more water from the body. The more you drink, the thirstier and more dehydrated you will.

More Articles:


“U.S. Office of Naval Research Ocean, Water: Temperature”.
Chester, Jickells, Roy. ”Marine Geochemistry”. Blackwell Publishing. ISBN 978-1-118-34907-6.
Stumm, W, Morgan, J. J., Aquatic Chemistry, An Introduction Emphasizing Chemical Equilibria in Natural Waters.

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