The "En" of Oceanography (Supplement)

Salt of Oceanography　The chemical meaning of the word "salt" is a compound that dissolves in water into positive and negative ionic components, but the meaning of "salt" in oceanography is slightly different. In oceanography, salinity is used as a parameter to calculate the density of seawater. In addition to the ionic components dissolved in water, there are also colloidal particles and dissolved gases in trace amounts that determine the density of seawater. Therefore, the "salinity" is the combined weight of the amount of residue left after evaporation of seawater and the amount of carbon dioxide that evaporates along with the water. An empirical formula has been established internationally to convert the electrical conductivity of seawater to salinity by determining a global standard. Because of the need to calculate ocean currents by detecting very small differences in density, it has been difficult to define “salinity", and the definition and empirical formula are still being improved (Kono, 2010). Salinity is a concentration by weight and is expressed as a per mil (‰) or percentage (%), but currently no unit is used in oceanography (if a unit is used, it is called psu: practical salinity unit). Incidentally, a strong electrolyte is a substance that is completely ionized when dissolved in water. When carbonic acid dissolves in seawater, it ionizes into two stages: "H₂CO₃ ⇆ HCO₃^－ + H⁺" and "HCO₃^－ ⇆ CO₃^2－ + H⁺" to reach equilibrium, and H₂CO₃ does not ionize completely to CO₃^2- and is classified as a weak electrolyte.