Here's why:
* Parts per thousand (ppt) is a convenient unit for expressing the salinity of seawater, which typically ranges from 30 to 40 ppt. It represents the number of grams of dissolved salts per 1000 grams of seawater.
* Grams per kilogram (g/kg) is another commonly used unit for expressing salinity. It is equivalent to ppt since 1 kg of seawater is equal to 1000 g.
While other units like percentage (%) or milligrams per liter (mg/L) are possible, they are not as commonly used for expressing salinity as ppt or g/kg.
