Why Is The Ocean Salty? | U.S. Geological Survey

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  1. Frequently Asked Questions
  2. Ocean
Why is the ocean salty?

Oceans cover about 70 percent of the Earth's surface and about 97 percent of all water on and in the Earth is saline—there's a lot of salty water on our planet. By some estimates, if the salt in the ocean could be removed and spread evenly over the Earth’s land surface it would form a layer more than 500 feet (166 meters) thick, about the height of a 40-story office building. But, where did all this salt come from? Salt in the ocean comes from rocks on land. Here's how it works:

From precipitation to the land to the rivers to the sea....

The rain that falls on the land contains some dissolved carbon dioxide from the surrounding air. This causes the rainwater to be slightly acidic due to carbonic acid. The rain physically erodes the rock and the acids chemically break down the rocks and carries salts and minerals along in a dissolved state as ions. The ions in the runoff are carried to the streams and rivers and then to the ocean. Many of the dissolved ions are used by organisms in the ocean and are removed from the water. Others are not used up and are left for long periods of time where their concentrations increase over time.

The two ions that are present most often in seawater are chloride and sodium. These two make up over 90% of all dissolved ions in seawater. The concentration of salt in seawater (its salinity) is about 35 parts per thousand; in other words, about 3.5% of the weight of seawater comes from the dissolved salts. In a cubic mile of seawater, the weight of the salt (as sodium chloride) would be about 120 million tons. A cubic mile of seawater can also contain up to 25 pounds of gold and up to 45 pounds of silver! But before you go out and try alchemy on seawater, just think about how big a cubic mile is: 1 cubic mile contains 1,101,117,147,000 gallons of water!

Learn more:

  • USGS Water Science School - Why is the Ocean Salty?
  • NOAA - Why is the ocean salty?

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A short video on why the ocean is salty.

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Why is the ocean salty?

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Related

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What is marine geology? What is marine geology?

Geology is the study of the Earth. This includes how the Earth was formed, how the Earth has changed since it was formed, the materials that make up the Earth, and the processes that act on it. Marine Geology focuses on areas affected by our oceans including the deep ocean floor, the shallower slopes and shelves that surround the continents, and coastal areas like beaches and estuaries. USGS...

What is marine geology?

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Geology is the study of the Earth. This includes how the Earth was formed, how the Earth has changed since it was formed, the materials that make up the Earth, and the processes that act on it. Marine Geology focuses on areas affected by our oceans including the deep ocean floor, the shallower slopes and shelves that surround the continents, and coastal areas like beaches and estuaries. USGS...

Learn More Bathymetry bounding Tomales Point

Where can I find bathymetric data? Where can I find bathymetric data?

The USGS has made bathymetric surveys for many coastal areas and for a few selected rivers and lakes in the U.S., including Yellowstone Lake, Crater Lake, and Lake Tahoe. Information and data for some of those studies is on the USGS Maps of America's Submerged Lands website. NOAA (National Oceanic and Atmospheric Administration) is the primary source of bathymetric data for the world's oceans. See...

Where can I find bathymetric data?

Where can I find bathymetric data?

The USGS has made bathymetric surveys for many coastal areas and for a few selected rivers and lakes in the U.S., including Yellowstone Lake, Crater Lake, and Lake Tahoe. Information and data for some of those studies is on the USGS Maps of America's Submerged Lands website. NOAA (National Oceanic and Atmospheric Administration) is the primary source of bathymetric data for the world's oceans. See...

Learn More Looking north across the southern end of the Great Salt Lake shoreline.

How is the salinity of Great Salt Lake measured? How is the salinity of Great Salt Lake measured?

The salinity of Great Salt Lake is measured by taking specific gravity and temperature measurements and comparing them to standardized values reported in a table. Specific gravity is measured in the field by testing a water sample with a device very similar to a battery or antifreeze tester. Learn more: Water-Resources Investigations Report for Great Salt Lake, Utah

How is the salinity of Great Salt Lake measured?

How is the salinity of Great Salt Lake measured?

The salinity of Great Salt Lake is measured by taking specific gravity and temperature measurements and comparing them to standardized values reported in a table. Specific gravity is measured in the field by testing a water sample with a device very similar to a battery or antifreeze tester. Learn more: Water-Resources Investigations Report for Great Salt Lake, Utah

Learn More Map of the world shows sea surface temperature anomalies on March 1, 2016 due to El Niño.

Where can I get current sea-surface temperature data? Where can I get current sea-surface temperature data?

The USGS has studied sea-surface temperature in many areas around the globe; you can find publications from these studies in the USGS Publications Warehouse and by searching on the Internet. World maps and data are available from other agencies, particularly at the NOAA's Sea Surface Temperature , and at the JPL Physical Oceanography Distributed Active Archive Center. For specific data covering...

Where can I get current sea-surface temperature data?

Where can I get current sea-surface temperature data?

The USGS has studied sea-surface temperature in many areas around the globe; you can find publications from these studies in the USGS Publications Warehouse and by searching on the Internet. World maps and data are available from other agencies, particularly at the NOAA's Sea Surface Temperature , and at the JPL Physical Oceanography Distributed Active Archive Center. For specific data covering...

Learn More Large waves crashing on rocks at beach.

What is the difference between a tsunami and a tidal wave? What is the difference between a tsunami and a tidal wave?

Although both are sea waves, a tsunami and a tidal wave are two different and unrelated phenomena. A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth ("tidal wave" was used in earlier times to describe what we now call a tsunami.) A tsunami is an ocean wave triggered by large earthquakes that occur near or under the ocean, volcanic...

What is the difference between a tsunami and a tidal wave?

What is the difference between a tsunami and a tidal wave?

Although both are sea waves, a tsunami and a tidal wave are two different and unrelated phenomena. A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth ("tidal wave" was used in earlier times to describe what we now call a tsunami.) A tsunami is an ocean wave triggered by large earthquakes that occur near or under the ocean, volcanic...

Learn More Multimedia Label List Grid All water on Earth in a sphere, placed over a "dry" globe All of Earth's water in a single sphere! All of Earth's water in a single sphere! All water on Earth in a sphere, placed over a "dry" globe July 16, 2019

All of Earth's water in a single sphere!

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This image shows blue spheres representing relative amounts of Earth's water in comparison to the size of the Earth. Are you surprised that these water spheres look so small? They are only small in relation to the size of the Earth.

By Water Science School All water on Earth in a sphere, placed over a "dry" globe July 16, 2019

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This image shows blue spheres representing relative amounts of Earth's water in comparison to the size of the Earth. Are you surprised that these water spheres look so small? They are only small in relation to the size of the Earth.

By Water Science School Why is the ocean salty? Why is the ocean salty? March 22, 2019

Why is the ocean salty?

Why is the ocean salty? Why is the ocean salty?

A short video on why the ocean is salty.

By Communications and Publishing March 22, 2019

Why is the ocean salty?

Why is the ocean salty?

Why is the ocean salty?

Why is the ocean salty?

A short video on why the ocean is salty.

By Communications and Publishing Full view of salt, sodium, chlorine sample Salt, Sodium, Chlorine Salt, Sodium, Chlorine Full view of salt, sodium, chlorine sample March 23, 2017

Salt, Sodium, Chlorine

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Mineral: Halite (NaCl)Primary mineral Commodity: Salt

By Energy and Minerals Mission Area, Mineral Resources Program, Communications and Publishing Full view of salt, sodium, chlorine sample March 23, 2017

Salt, Sodium, Chlorine

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Mineral: Halite (NaCl)Primary mineral Commodity: Salt

By Energy and Minerals Mission Area, Mineral Resources Program, Communications and Publishing A large wave crashing on the reef in the background, beach sand, birds, and boulders in the foreground. Large wave crashing on the reef at Laysan Island Large wave crashing on the reef at Laysan Island A large wave crashing on the reef in the background, beach sand, birds, and boulders in the foreground. October 1, 2015

Large wave crashing on the reef at Laysan Island

Large wave crashing on the reef at Laysan Island Large wave crashing on the reef at Laysan Island

A large wave crashes on the reef at Laysan Island, located in the Northwestern Hawaiian Islands.

By Natural Hazards Mission Area, Coastal and Marine Hazards and Resources Program, Pacific Coastal and Marine Science Center A large wave crashing on the reef in the background, beach sand, birds, and boulders in the foreground. October 1, 2015

Large wave crashing on the reef at Laysan Island

Large wave crashing on the reef at Laysan Island

Large wave crashing on the reef at Laysan Island

Large wave crashing on the reef at Laysan Island

A large wave crashes on the reef at Laysan Island, located in the Northwestern Hawaiian Islands.

By Natural Hazards Mission Area, Coastal and Marine Hazards and Resources Program, Pacific Coastal and Marine Science Center Image: Mountain of Salt Mountain of Salt Mountain of Salt Image: Mountain of Salt January 1, 2002

Mountain of Salt

Mountain of Salt Mountain of Salt

This photo shows a road salt storage stockpile that is awaiting use for pavement deicing, Port of Milwaukee, WI. The use of salt to deice pavement can be harmful to aquatic life in urban streams. The USGS is involved in studies that focus on the influence of winter runoff on aquatic ecosystems.

By Contaminant Biology, Toxic Substances Hydrology, Environmental Health Program, Communications and Publishing Image: Mountain of Salt January 1, 2002

Mountain of Salt

Mountain of Salt

Mountain of Salt

Mountain of Salt

This photo shows a road salt storage stockpile that is awaiting use for pavement deicing, Port of Milwaukee, WI. The use of salt to deice pavement can be harmful to aquatic life in urban streams. The USGS is involved in studies that focus on the influence of winter runoff on aquatic ecosystems.

By Contaminant Biology, Toxic Substances Hydrology, Environmental Health Program, Communications and Publishing Publications Items per page 6 12 Label September 26, 2013

Is a salinity monitoring network "Worth its salt"? Is a salinity monitoring network "Worth its salt"?

Saltwater intrusion threatens the water supplies of many coastal communities. Management of these water supplies requires well-designed and properly maintained and operated salinity monitoring networks. Long-standing deficiencies identified in a salinity monitoring network in southwest Florida during a 2013 study (Prinos, 2013) help to illustrate the types of problems that can occur in... Authors Scott Prinos By Water Resources Mission Area, Caribbean-Florida Water Science Center (CFWSC) January 1, 1994

Why is the ocean salty? Why is the ocean salty?

All water, even rain water, contains dissolved chemicals which scientists call "salts." But not all water tastes salty. Water is fresh or salty according to individual judgment, and in making this decision man is more convinced by his sense of taste than by a laboratory test. It is one's taste buds that accept one water and reject another. Authors Herbert Swenson News Items per page 6 12 Label Celebrate June as National Oceans Month June 4, 2015

Celebrate June as National Oceans Month

June marks National Oceans Month, a month dedicated to spreading awareness of Earth’s oceans and coastal ecosystems.

Read Article Study Aids Water Managers Battle Saltwater Intrusion May 22, 2014

Study Aids Water Managers Battle Saltwater Intrusion

Scientists are using a cadre of new weapons in the battle against an old nemesis – saltwater intrusion. Read Article

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