What does 35 percent mean when applied to sea water?

It is measured as the total amount of dissolved salts in parts per 1,000. ... The salinity of normal ocean water is about 35 parts per 1,000, total dissolved solids. This is written as 35‰ or 35 ppth. A salinity of 35‰ is the same as 3.5%. The symbol resembles a percentage sign (%), but percent means per 100.