(a) Explain the term salinity (b) Describe three factors that cause variations in the salinity of seas and oceans (c) Outline three ways in which oceans are...

(a) Explanation of salinity

Salinity is the degree of saltiness of sea or ocean water, that is, the total amount of dissolved mineral salts (chiefly sodium chloride) present in a given quantity of water. It is usually expressed in grams of salt per 1000 grams of water (parts per thousand, \(\text{ppt or } ‰\)). The average salinity of the oceans is about \(35‰\) (35 grams per 1000 grams of water).

(b) Three factors causing variations in salinity

• Rate of evaporation: Where evaporation is high (hot, dry tropical and enclosed seas), water is removed but salt is left behind, so salinity is high (e.g. the Red Sea and the Dead Sea). Where evaporation is low, salinity is lower.
• Amount of fresh water added: Heavy rainfall, the inflow of large rivers, and the melting of ice add fresh water and dilute the salt, lowering salinity. Areas near river mouths and the equator therefore have lower salinity.
• Movement and mixing of water: Ocean currents and the free movement of water in the open sea mix and even out salinity, while enclosed and land-locked seas with little exchange develop extreme (high or low) salinity.

(c) Three ways oceans are important to man

• They are a major source of food (fish, shellfish and other sea foods) and of minerals such as common salt.
• They serve as cheap highways for transport and trade by ships between countries and continents.
• They influence climate (moderating temperatures and providing moisture for rainfall) and are a source of energy, petroleum and tourism.