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why is the ocean salty|guy holding ocean monq r

Nature & Outdoors

Why Is the Ocean Salty?

A walk along the beach is a treat for all the senses. You feel the sun on your face, the wind in your hair, and the sand between your toes. Far out to sea, you see a beautiful landscape that seems almost endless. You can hear the waves crashing, and you can smell the scent of the ocean so strongly you can almost taste it. The scent of the sea is a unique blend of marine plants, aquatic life, and salty water.

guy holding ocean monq r Simply breathing this unique scent can leave you feeling more relaxed.This unique blend of essential oils recreates the feeling of the ocean breeze.

Why is the ocean salty? When you think about all the different sources of water - ponds, lakes, rivers, streams - almost all of them are freshwater. What makes the ocean different?

Where All That Salt Comes From

Oceans cover 70% of earth’s surface and account for about 97% of all water on earth. The average salt content of ocean water is 35 parts per thousand, about 3.5 percent of the weight of seawater. 1 Considering how vast the ocean is, that is a lot of salt. Some scientists have estimated that if you took all of the salt out of the ocean and spread it out evenly on earth’s surface, it would form a layer more than 500 feet thick and 40 stories high! 2

Where did all of this salt come from? Most of it comes from the land, yet some of it comes up from the bottom of the sea.

Salt From the Land

When it rains, the rainwater contains small amounts of carbon dioxide from the surrounding air. This makes rainwater slightly acidic, due to the carbonic acid which is formed through carbon dioxide and water. As rainfall erodes the rock, the acidity of the rain chemically breaks down the rock. This process creates ions, which are washed into streams, rivers, and finally into the ocean.

Some of the ions are used up by different organisms in the ocean and are no longer present in the water. Others don’t get used up and concentrations of them increase over time. Chloride and sodium are two of these ions, and together they make up 90% of all the ions in the ocean. Sodium chloride - also known as ‘salt’. 3

Salt From the Bottom of the Sea

Rainfall isn’t the only reason why the ocean is salty. Hydrothermal vents located on the crest of oceanic ridges also add dissolved minerals to the sea. Ocean water seeps into the rocks in the oceanic crust, then becomes hotter, dissolves minerals in the crust, and flows back into the ocean via hydrothermal vents.

These vents are a large reason why the ocean’s salinity stays relatively stable, even though salt is constantly flowing into it. Scientists have estimated that based on the amount of hydrothermal fluids flowing out of these vents, the entire volume of the ocean could go through the oceanic crust in approximately 10 million years. The oceanic basalt actually removes some of the dissolved minerals from the water, even though the process is adding some as well. Other dissolved salts eventually end up as sediment on the sea floor.

Volcanoes erupting under water is one more way that dissolved minerals get into the sea. Ocean water interacts with hot rock, dissolving some of the minerals and letting them out to sea. 4

Why Isn’t Freshwater Salty?

If rainfall is a large cause of the salt in the sea, why aren’t all bodies of water salty? One of the main reasons is because rivers and streams are constantly moving. Although trace amounts of sodium and chloride are always present, they have a significant amount of fresh rainwater always coming in. Most lakes are not salty for the same reasons. Rivers often feed them, as well as draining them.

Water is constantly flowing in and out of these bodies of water, while water is flowing into the ocean and only leaving by evaporation. Since salt does not leave by evaporation, the concentration builds up.

If a lake doesn’t have any outflow, it will also become salty. This is true for the Great Salt Lake in Utah and the Dead Sea in Jordan.

Sea Salt vs Table Salt

Not all of the salt we eat comes from the ocean. The most popular type of salt is table salt, which is from underground salt deposits. Table salt is more heavily processed, usually contains an additive to prevent clumping, and often contains added iodine.

On the other hand, sea salt comes from evaporated ocean water. It usually involves little processing, which leaves behind trace elements and minerals depending on its source. The minerals add different flavors and color to the salt.

The next time you’re salting your meal, take a moment to appreciate the long process that salt went through to get to your dinner table.

Photo credits: yari2000/

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