Salt in the ocean comes from rocks on land

water running over rocks

Image courtesy of the National Park Service.

Rain that falls on land contains some dissolved carbon dioxide from the surrounding air. The carbon dioxide and water form carbonic acid, which in turn breaks down rocks on land. This process creates ions, or electrically charged atomic particles. These ions are carried away in runoff to streams and rivers and, ultimately, to the ocean.

Two of the most prevalent ions in seawater are chloride and sodium. Together, they make up over 90 percent of all dissolved ions in the ocean. Sodium and chloride are 'salty.'

The concentration of salt in seawater (salinity) is about 35 parts per thousand. Stated in another way, about 3.5 percent of the weight of seawater comes from the dissolved salts; in a cubic mile of seawater, the weight of the salt (in the form of sodium chloride) would be about 120 million tons.

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 thick, about the height of a 40-story office building.


Did You Know?

The Florida Keys are the driest areas in Florida with an average of 124.5 centimeters or 39.9 inches of precipitation per year. The highest monthly rainfall occurs in September and the lowest in March.