Why is the sea salty?

Seawater is really pure water in which compounds have dissolved. Salts account for most of these dissolcved substances. The total amount of salts dissolved in seawater is known as salinity, which is measured as the number of parts of salt in a thousand parts of water. For example, a 1,000-gram sample of seawater will usually contain 35 grams of dissolved salts and, as a result, has a salinity of 35 parts per thousand.

Salinity levels range from near zero at river mouths, where freshwater is flowing into the ocean, to more than 40 parts per thousand in the Red Sea and Persian Gulf. Bouyancy, the ability to float, is higher if the salinity of the water is higher. Thus, it is the salinity of the water that is responsible for our beingg able to float easily in seawater than in freshwater.

Seawater contains all the dissolved substances -- including inorganic salts, compounds derived from living organisms, and dissolved gases -- necessary for the growth and well-being of plant and animal life. More than 99 percent of these dissolved materials are inorganic salts present as ions, which are atoms or groups of atoms that carry a very slight electric charge. Major ions in ocean water include chlorine (Cl), sodium (Na), sulfur (S), magnesium (Mg), calcium (Ca), and potassium (K).