Salinity of the Oceans
Introduction: Different bodies of water have different amounts of salt mixed in, or different
salinities. Salinity is expressed by the amount of salt found in 1,000 grams of water (ppt). The
average ocean salinity is 35 ppt. This number varies between about 32 and 37 ppt. Rainfall,
evaporation, river runoff, and ice formations cause the variations. For example, the Black Sea is so
diluted by river runoff, its average salinity is only 16 ppt. Salinity of the top layer of the ocean is
closely linked with precipitation and evaporation. Evaporation leaves behind dissolved salts
increasing salinity and precipitation "freshens" the top ocean layers. So, salinity is high in mid-
latitudes where evaporation is high and precipitation is low. Salinity is low near the equator
because precipitation is so high. Very high latitudes can also see decreases in salinity where sea
ice melts and "freshens" the water.
1) What is the relationship between salinity and evaporation?
2) Where is ocean salinity high? Why is it high in these locations?
3) Where is ocean salinity low? Why is it low in these locations?