- The vast majority of the oceans and seas is water, accounting for more than 99% of the atoms it contains. The second biggest component is salts and dissolved minerals. Regular table salt (NaCl) is the largest contributor of all dissolved ions (about 0.3%). However, salinity varies depending on the body of water; the Red Sea is one of the saltiest, with 40ppm salt, and oceans nearing the ice caps are the least saline, at about 32ppm salt.
- After water and salt, the most common elements found in sea water are magnesium, sulfur, potassium, calcium, bromine, carbon, nitrogen and fluorine, all of which stand at more than 10ppm. Among the common ions found are sulfate (SO4), bicarbonate (HCO3) and borate (BO3). Other elements and ions are dissolved, but mostly in trace amounts. Mercury can be of concern, however, because though it appears in trace amounts in the water, it can increase in higher rings of the food chain through biomagnification.
- It is difficult to get accurate numbers for the amounts of various dissolved gases in sea water, but approximate numbers give a picture. Dissolved nitrogen accounts for about 10mL, oxygen about 5mL, and carbon dioxide about 40mL per liter of sea water. The composition can vary greatly depending on the season, depth, temperature and plant growth in the vicinity.
- Seawater is teeming with microscopic life, though most of it is completely harmless. This life includes plankton, bacteria and viruses. It's been estimated that a teaspoon of sea water can contain as many as 10 to 100 million viruses, and bacteria can reach concentrations of up to 10 million per mL.
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