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Why is the Ocean Salty?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

Ocean water is salty because it contains high concentrations of dissolved minerals known collectively as salts. Around 3.5% of ocean water is comprised of salts, depending on where in the world one is; equatorial waters tend to be saltier, while northern waters are slowly becoming more fresh. There are a number of factors which make the ocean salty, and scientists are very interested in the salt content of the ocean, because it contributes to the flow of currents through the ocean, in a process known as thermohaline circulation.

One of the reasons that the ocean is salty has to do with the ocean's floor, which contains a huge assortment of minerals and dissolved organic material which is slowly eroded and stirred up by the movements of the ocean. As the ocean eats away at the ocean floor, it increases the salt content. The ocean floor is also constantly renewing itself, another way to make the ocean salty, as seafloor spreading releases even more dissolved minerals into the water, in the form of emissions from hydrothermal vents and cracks in the seafloor.

Sea salt.
Sea salt.

Another thing that makes the ocean salty is the water runoff which pours into the ocean. This might seem counterintuitive to you, as rivers, streams, and lakes probably taste fresh to you. However, this water also contains dissolved salts, although the concentration is lower than that in the ocean. These salts make their way to the ocean with the river water, which eventually evaporates from the ocean to fall back to Earth again as rain, repeating the process.

Salt comprises about 3.5% of the water in the ocean.
Salt comprises about 3.5% of the water in the ocean.

The reason these salts do not build up in things like lakes is because inland bodies of water have an outlet. What makes the ocean salty is the slow concentration of salts over time, because the salts in the ocean have nowhere to go. Lakes and streams, on the other hand, are constantly recirculating their water. To find out what happens when a lake has no outlet, you can look at the Dead Sea, which has a famously high concentration of salts.

The salt content of the ocean is increased as the ocean floor erodes.
The salt content of the ocean is increased as the ocean floor erodes.

Now that you know what makes the ocean salty, you may be interested in experimenting with your own personal threshold for tasting salt. If you drink a glass of water out of the tap, you will probably perceive it as “fresh.” In fact, tap water has a number of dissolved salts, and these salts are what give tap water its flavor. If you don't think that water has flavor, try drinking a glass of distilled water, which will taste incredibly stale and flat by comparison. If you add a pinch of regular salt to distilled water, it will taste significantly more fresh; the same pinch added to fresh water may make it taste a bit salty to you.

Frequently Asked Questions

Why is the ocean salty?

The ocean's saltiness comes from minerals washed out of rocks on land. Rainwater, slightly acidic due to dissolved carbon dioxide, erodes rocks, releasing ions like sodium and chloride into rivers that eventually flow into the sea. Over millions of years, these ions have accumulated, making the oceans salty.

What are the main sources of salt in the ocean?

Main sources of salt in the ocean include runoff from rivers, which carry dissolved salts from eroded rocks, volcanic activity that emits gases rich in chlorine, and hydrothermal vents on the ocean floor that release minerals. Together, these processes contribute to the ocean's salinity.

How does the salinity of the ocean affect marine life?

Salinity influences the buoyancy, temperature, and density of seawater, which in turn affects marine life. Organisms have adapted to specific salinity ranges; too much or too little salt can disrupt their cellular processes. For example, osmoregulation, the process of maintaining an internal balance of salt and water, is crucial for marine species' survival.

Does the salinity of the ocean change over time?

Yes, ocean salinity can change over time due to various factors such as the water cycle, ice melting, and precipitation patterns. Climate change is altering these factors, leading to shifts in salinity. For instance, melting polar ice is freshening the waters in those regions, while other areas may become saltier due to increased evaporation.

Can the ocean ever become too salty?

While the ocean's salinity is generally stable due to the water cycle balancing the salt content, extreme scenarios could disrupt this balance. If evaporation significantly exceeds precipitation and river input, certain areas could become hypersaline, like the Dead Sea. However, this is unlikely on a global scale due to the vastness of the oceans.

Is the salinity the same in all parts of the ocean?

No, salinity varies across different parts of the ocean. It is typically higher in regions with high evaporation rates and lower freshwater input, such as the subtropics. Conversely, areas near the equator, with heavy rainfall, or where freshwater from rivers and melting ice dilutes the seawater, tend to have lower salinity levels.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

Discussion Comments

anon175259

i need to know what percent of the salt in the ocean comes from the rivers flowing into them? I would bet it's 75 percent, the rest coming from the sea floor, volcanic vents, etc.

submariner

@GiraffeEars- The process of weathering and erosion causes the ocean to be salty. Mechanical, chemical, and biological weathering break, dissolve, and pulverize the rock. Once the minerals that make the ocean salty are exposed, erosion moves these minerals into the hydrosphere. Waves cause mechanical and chemical weathering that erodes minerals into the ocean. Rains wash weathered minerals into lakes, which in turn are washed into the ocean through rivers and streams.

The minerals that enter the ocean are either dissolved, sink to the bottom, or have been weathered enough to be suspended in solution. Water soluble minerals will dissolve in the ocean, while wind, tides, and currents influence the turbidity of the oceans. These geologic processes are what make ocean water salty.

GiraffeEars

So I understand that the ocean is salty because of minerals, but can someone explain the process to me in a little more detail? How does the ocean get salty from rivers? What is the geologic process that creates this saltiness, and why don't the minerals simply sink to the bottom of the ocean?

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    • Sea salt.
      By: Jiri Hera
      Sea salt.
    • Salt comprises about 3.5% of the water in the ocean.
      By: masa
      Salt comprises about 3.5% of the water in the ocean.
    • The salt content of the ocean is increased as the ocean floor erodes.
      By: Sukrita
      The salt content of the ocean is increased as the ocean floor erodes.