Ocean water is salty primarily due to the large amounts of chloride and sodium on land which are dissolved by rainfall and carried to the sea by rivers and streams. Hydrothermal vents and underwater volcanoes located on the seabed also contribute dissolved salts to the ocean.
All water contains dissolved salts; however, it is the large concentration of salts in seawater that make it discernible to human taste. Of the estimated 50 quadrillion tons of dissolved solids in the ocean at any given time, 90 percent of them are chloride and sodium. In comparison to fresh lake water, which contains approximately one sixth of an ounce of salt per cubic foot, the same volume of seawater contains approximately 2.2 pounds of salt and is 220 times saltier than fresh lake water. It is estimated that rivers carry 4 billion tons of dissolved salts to the ocean annually. The weight of the salt in one cubic mile of seawater is approximately 120 million tons. If all of the salt in the ocean were removed and distributed evenly over the surface of the Earth, scientists estimate it would form a solid layer over 500 feet thick or about as tall as a 40-story building.