Why is the Ocean Salty?

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Statistics indicate that the oceans account for about 97% of the Earth’s water.

Also, they cover over 71 percent of the Earth’s surface. Out of all that sea water, 2-3 percent has ice caps and glaciers, while 1 percent is fresh water. The rest? Piecing salty water.

So, what makes large parts of the Earth’s oceans so salty?

Why are Oceans and Seas Salty?

To answer this question it’s imperative to look at how the earth got formed billions of years ago. Its crust started to cool and the first solid land masses appeared. At this time, there wasn’t any ground level water, while the atmosphere was quite thin.

The only water present on earth was in form of vapor. Once the earth became cool enough, stable bodies of water appeared, but they weren’t as salty as the oceans of today. And this is simply because of the water cycle process.

What is the Water Cycle?

This is the procedure that governs earth water’s accumulation, evaporation, condensation and precipitation.

As the water cycle occurs over and over, minerals from rocks as well as other sources get amassed into the water. If anything, water evaporating from the earth land masses, as well as salty and fresh water sources, is usually free from impurities (for the most part).

As it penetrates the atmosphere, the water compounds with the carbon dioxide molecules in it to form carbolic acid. In other words, the water becomes slightly carbonated with mild acidic properties. When it falls back to the surface in the form of rain, the acidity dissolves the soil albeit slowly but steadily.

This makes the minerals in the soil to get dissolved in the water. In essence, rain water carries away sodium and chloride ions as it passes.

Natural Waterways

As you know, rain as well as ground water flow into enormous and ‘static’ water accumulations known as oceans and seas.

Here, evaporating water sheds its baggage leaving behind the salt-forming ions on the earth surface. In water bodies like rivers, streams, and lakes, there is an influx of fresh water, making it difficult for the salt-forming elements to settle because they get carried forth and swept up by the never-ending streams.

But when this fresh water arrives at the ocean, its movement stops. This kick starts the sedimentation of salts. Eventually, sodium calcium as well as other salt-forming elements compounds to form the salt that makes sea water extremely salty.

Notably, 78% of global precipitation and 86% of global evaporation occur over the ocean.

Measuring the Saltiness in Sea Water

Different oceans and seas have different saltiness levels.

The saltiness (salinity) in sea water (salinity) gets measured in ppt (parts per thousand) or psu (practical salinity units). Most seas and oceans have a salinity of about thirty-five ppt (35 parts of dissolved salt per thousand parts of water). That is equal to 35000 ppm or 3.5% salinity.

Even so, the salinity of sea water usually ranges from 30,000 ppm to 50000 ppm.

On the other hand, fresh water has merely about 100 ppm (100 parts of salt per millions parts of water). In fact, water supplied in the US gets restricted to a 500 ppm salinity level, while the official concentration limit is 1000 ppm for drinking water. What’s more, the salinity limit for irrigation water lies at 2000 ppm.

The Level of Saltiness in Different Seas and Oceans

According to a NASA Aquarius map shows that oceans in the subtropics have a higher salinity level.

Notably, there’s a lower average salinity in the Indian and Pacific oceans compared to the Atlantic. Also, the rainy belts near the equator have quite a low salinity level, especially the northernmost Pacific Ocean region.

The Mediterranean Sea features arguably the highest salinity level. And this is largely because the sea has no connection with the rest of Earth’s oceans. Additionally, this sea ripples with warmer temperatures, which leads to frequent evaporation.

Remember, once sea water evaporates, the salt remains. And the cycle occurs over and over again.

It’s important to realize that the salinity level of an ocean gets largely determined by the region’s ocean circulation, river outflow, evaporation over the ocean, as well as large-scale patterns of rainfall.

Why Salinity is Important?

Salinity affects the density of sea water.

Water that has a lower salinity level is less dense as well as lighter, and will rise above the denser and more saline water. This layering of sea water ultimately affects the ocean current movements. What’s more, it can affect marine life in the sea because some species survive on a specific intake of salty sea water.

For example, whales don’t have kidneys that can process excess salt, making their chances of survival in highly saline water quite minimal. Still, animals like sea birds and sea otters can survive in extremely salty regions like the Mediterranean Sea because of their respective salt glands and kidneys.

These organs enable them to deal with the extra salt.

Why You Shouldn’t Drink Sea Water?

It’s quite an irony that sea water is widely available, but you shouldn’t drink it.

That’s mainly because your body doesn’t have the capacity to process all that salt. To clarify, the human body needs salt, but in small amounts to maintain a chemical balance. When you ingest more salt, the kidneys get rid of the extra amounts by extraction via urine.

Now sea water is way salty than the urine you excrete, meaning that drinking it is deadly. Your body will need to get rid of the extreme levels of salts, which requires more water than is present in the sea water you’ve drank. As such, your cells end up releasing more water to compensate for the required levels, leading to faster dehydration.

Therefore, drinking sea water speeds up your demise.

Folklore Answers to Why the Sea is Salty?

While our ancestors didn’t have the technology and education available today, they still had the same questions.

Thus, different communities developed their own interesting stories on how the sea became so salty. Here are some of the most famous traditional tales:

Denmark’s Miraculous Coffee Mill

According to this legendary tale, there once lived a small boy named Hans. Hans resided with at his grandmother’s place because he was an orphan. One day, his grandmother became so sickly, and just before her demise, she gave Hans her most prized asset- the coffee mill.

Her last words were that if Hans ever needed anything, he ought to ask the mill and it will grind it for him. Also, the mill would grind everything he wanted, but it needed a special command to stop.

Expectedly, the mill changed the little boy’s life for the better and he survived without any hassles after his grandma passed on.

When he was of age, Hans resolved to see faraway places by sailing the world. So he got himself a job aboard one of his country’s ships but things were quite murky right from the off. His sailing counterparts didn’t like his guts and so under-fed him out of jealousy.

Nonetheless, Hans wasn’t bothered with the other sailors’ actions, since he had his precious coffee mill to provide everything he needed. When the rest of the crew got wind of this mill, they decided to steal it and throw Hans into the sea.

They then commanded the mill to lots of salt so that they get rich by selling it. Unfortunately, they didn’t know there was a special command to make the mill stop grinding the salt. So the mill grinded until there was enough salt to sink the ship.

And it’s still grinding to date.

Philippines’ Salt Maker and the Ocean

There once lived a man named Pedro.

Pedro was so poor that he had to constantly borrow from his neighbours and friends just to get by. He would always promise to repay the debts- a promise even his debtors knew he wouldn’t keep.

One day, he rowed to a nearby island in the hope meeting new people. As he strolled about the abandoned island, he came across an abandoned lamp. He picked and cleaned it, all the while wondering how much his newly found treasure can earn him.

Soon enough, a genies popped out of the lamp and offered to save him from all the poverty. How? It would grind enough salt for him and his kinsmen to sell and become extremely rich.

But there were conditions.

First, Pedro had to promise that he will share his fortune with friends and family. Secondly, he could only access the salt at the island since the lamp couldn’t leave the area.

After eagerly agreeing to all the conditions, Pedro carried as much as salt as possible and for a while he would feed his entire family well. But it didn’t take long for greediness to settle in his heart and he decided to carry the lamp home.

As he rowed home, the lamp spewed too much salt that the boat sank. So the region’s people believe that it is the lamp is producing all the salt present in the seas today.

Oceans and Seas to Continue Being Salty

Since the water cycle process is unlike to stop any time soon, earth’s seas will continue becoming saltier over time.

So always prepare yourself for highly saline water every time you hit the coast.


This is George, the Aquaman, editor at AquaMantra. I'm a water quality analyst by profession, and used to work at one of the largest water bottler company.
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