The dissolved constituents found in the ocean come from the transport of terrestrial salts in weathered sediments by leaching and stream runoff. Sea water is a mixture of water and various salts. The presence of salt in sea water allows ice to float on top of it. These gases enter the ocean from the atmosphere and from a variety of organic processes. Sea water changes its density with variations in temperature, salinity, and ocean depth.
Sea water is least dense when it frozen at the ocean surface and contains no salts.
Highest sea water densities occur at the ocean floor. Atmospheric circulation drives the movement of ocean currents. Within each of the three ocean basins, the patterns of these currents are very similar. In each basin, the ocean currents form several closed circulation patterns known as gyres. A large gyre develops at the subtropics centered at about 30 degrees of latitude in the Southern and Northern Hemisphere.