WATER MASS

(Oceanography) An oceanographic term that refers to a large body of water whose density characteristics are distinct from the surrounding aquatic environment because of inherent temperature or salinity differences. Water masses are present in all oceans and are formed where water flows from one type of climatic or physiographic region into another. The North Atlantic Current is an example of a water mass distinguished by a difference in temperature. It is a relatively warm water body that retains its identity as far north as the Arctic Circle. The huge freshwater volume expelled by the Amazon River into the southern Atlantic Ocean is an example of a water mass distinguished by a difference in salinity.