There are five oceans on Earth. The Pacific Ocean is the biggest Atlantic, Indian, Southern, and Arctic ocean. Some oceans are saltier, but around 3.5 percent of ocean water is salt. The seafloor has vast amounts of minerals that are constantly being switched worlds 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 contain about 3.5 percent salt, equating to 50 million billion tons of salt in our seas. Packing all that salt onto the Earth’s land would create a layer 152 meters high.
Why is seawater salty?
The saltiness of seawater is primarily due to the presence of dissolved salts and minerals. Here are the main reasons why seawater is salty:
Dissolved Salts: Over millions of years, rainwater and runoff from land carry minerals and salts from rocks into rivers, which eventually flow into the ocean. The ocean acts as a large basin that collects these dissolved salts and minerals, resulting in the salinity of seawater.
Weathering and Erosion: Minerals and salts on land are broken down and transported into water bodies through weathering and erosion processes. These dissolved salts include sodium, chloride, magnesium, calcium, and potassium.
Volcanic Activity: Underwater volcanic activity contributes to the salinity of seawater. Volcanic eruptions release gases and minerals into the ocean, increasing the concentration of dissolved salts.
Hydrothermal Vents: Hydrothermal vents, found along mid-ocean ridges, release hot mineral-rich water into the ocean. These hydrothermal fluids contain various dissolved salts, including sulfides and metal ions, which can contribute to the overall salinity of the seawater in those areas.
Evaporation: When water evaporates from the ocean’s surface due to solar heating, it leaves the dissolved salts behind, increasing the concentration of salts in the remaining water. This process occurs primarily in arid or semi-arid regions where evaporation rates are higher than precipitation rates, such as saltwater lakes or enclosed seas like the Dead Sea.
Some salts dissolve 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 chemical reactions, and the water loses 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. 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 saltier water.
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 that of the rivers coming into it. A black smoker is a microcrystal 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 from rivers and trading them for new chemicals like sodium chloride, calcium chloride, etc. It occurs all along the mid-ocean ridge that stretches around the planet like the seam of a baseball. Also, thousands of magma chambers are down there, and the waters get into them.
Natural water resources
One fantastic thing is why the oceans are salty, but other waters like lakes and rivers aren’t. The water in lakes and rivers is fresh. When scientists study any water they find on Earth, that’s one of the first things they do. They figure out if it is salt water, 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. They discovered something surprising. Even though in lakes and rivers water has a small amount of salt. But the water in lakes and rivers is a little bit salty. 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 has zero salts in the raindrops. So rainwater is 100% entirely freshwater. Scientists discovered that once rainwater hits the ground, like when it forms puddles or trickles into streams and rivers, it becomes slightly salty. So then, something about the ground must make the water in lakes and rivers slightly salty.
- Rain collects carbon dioxide from the atmosphere When it forms and poses through the air. 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 determine 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 bit 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 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 the river and lake water only carry a tiny amount of salt. That water’s been flowing for years and years down into the ocean. All that salt it carries keeps getting added to the ocean over and over, where it probably never leaves.
The salt becomes more concentrated in the sea because the sun’s heat distills the ocean surface, leaving the salt client. Across the globe, rivers deposit 4 billion tons of salt into our oceans every year. So surely seas must be getting saltier. Certainly, the oceans have brought a lot saltier since their ancient beginnings. As much salt is deposited on the ocean floor, it comes 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, its hot evaporation rates exceed the amount of rainfall. So water here is much saltier. 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 a rise in salinity levels. It 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 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. Life would undoubtedly differ in oceans without this influx of salt and minerals from rivers and streams.
Properties of saltwater
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 wide varieties. That is because salt is a compound held together by an ionic bond. What happens if 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.
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 has no outlets. The salt slowly builds up in the water, 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 ten 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 through 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; your kidneys must dilute it 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 be.
“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.
Table of Contents