1. Salinity is related to the concentration of dissolved salts in seawater.
In the past, salinity of seawater was measured by evaporating the water and weighing the amount of salt remaining. Since that approach is difficult and inaccurate, electrical conductivity of seawater is now used to measure salinity.
* Conductivity increases as salt content of the water increases.
* Conductivity gives very accurate salinity data: 35.0000X.
* Conductivity (and temperature and depth) are measured by instruments called CTDs (Conductivity Temperature Depth). These instruments can make thousands of measurements/hour.
* Salinity, temperature, and depth (pressure) can be used to calculate density, which is important to understanding vertical circulation of the water.
* Salinity is greatest in warm, tropical surface waters, where there is more evaporation than precipitation. It is lowest where there are large inputs of freshwater from rivers.
Salinity has no units. (The PSU or “practical salinity unit” is incorrect, although frequently used.)
* Salinity is approximately equal to the weight, in grams, of salt dissolved in 1000 g of seawater. This would be the salt concentration in parts per thousand (‰).
* Average ocean water has a salinity of 35.0.
* This means that 1000 g of average seawater contains 965 g of water and 35 g of salts.
2. Salts consist of ions.
Cations have a positive electrical charge. Anions have a negative electrical charge. Salts are electrically neutral because the cation and anion charges are opposite and equal.
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