Salinity is used to measure the amount of salt in water. This measurement is critical for many marine species because they can only live within a certain salinity range. Salinity varies based on depth and location. For example, the Atlantic Ocean has its highest salinity in the North Atlantic at 35.5 and its lowest in the South Atlantic at 34.5.

Salinity is measured in grams of salt per kilogram of water. For example a salinity of two would mean there were two grams of salt in every kilogram of water.

Salinity increases as depth of the water increases because higher concentrations of salt increase the density of water.

The halocline layer is found between the surface layer and the deep sea layer of water. This is the level at which the salinity of water rises the fastest.

The salinity of water can be determined by how easily electricity travels through it. The higher the conductivity the higher the salinity.

Many fish require a certain salinity level to live so in fish tanks the salinity level must be kept constant.