seawater, Water that makes up the oceans and seas. Seawater is a complex mixture of 96.5% water, 2.5% salts, and small amounts of other substances. Much of the world’s magnesium is recovered from seawater, as are large quantities of bromine. In certain parts of the world, sodium chloride (table salt) is obtained by evaporating seawater. In addition, desalted seawater can theoretically furnish a limitless supply of drinking water, but the high processing costs are prohibitive. Large desalination plants have been built in dry areas along seacoasts in the Middle East and elsewhere to relieve shortages of fresh water.
seawater summary
Learn about the chemical and physical properties of seawater
sea ice summary
sea ice, Ice formed from frozen seawater in polar regions. Most sea ice occurs as pack ice, which drifts across the ocean surface; other types of sea ice include fast ice, which is attached to coasts and sometimes the seafloor or between grounded icebergs, and marine ice, which forms at the bottom of ice shelves in Antarctica. The sea ice of the Northern Hemisphere covers about 3 million sq mi (8 million sq km) in September and about 6 million sq mi (15 million sq km) in March. Sea ice in the Southern Hemisphere ranges from about 1.5 million sq mi (4 million sq km) in February to about 8 million sq mi (20 million sq km) in September.