As far as I know, the ocean has separated layers collectively called a Halocline (halo = salt, 'cline' as in slope/grade). Water can hold more if its cold and therefor heavy, thus sinks (more pressure). Warm water rises upward and can't hold onto things, thus less dense on the surface. The "cline" here is the separated vertical levels (like layers) that differ in salinity. So generally, cold, dense water holds more salt at the bottom and warm, non-dense, less-salty water at the top.