(i) The degree of concentration of salts in the sea water is called salinity.
(ii) It is usually expressed in terms of parts per thousand (ppt or %0).
(iii) Salinity varies both horizontally and vertically.
(iv) The influence of temperature on ocean salinity depends upon the heating up of the surface water, which varies from tropics to polar regions

(i) Of all the movements of the oceans, sea waves are considered to be the strongest.
(ii) Sea waves are ripples on water caused when winds blow over the sea.
(iii) The height of these waves depends on the speed of wind, its duration and the direction from which they blow.
(iv) Sometimes waves are also caused by tremors felt on the ocean floor.
(v) Such waves are quite destructive and called Tsunami

(i) The Earth's water is not static.
(ii) It is always in motion.
(iii) This continuous movement of water on, above and below the earth's surface is called the Hydrological Cycle.
(iv) The three major processes involved in the water cycle are evaporation, condensation and precipitation.

(i) Salt in the ocean comes from rocks on land.
(ii) The rain that falls on the land contains some dissolved carbon dioxide from the surrounding air. This causes the rainwater to be slightly acidic due to carbonic acid (which forms from carbon dioxide and water).
(iii) As the rain erodes the rock, acids in the rainwater break down the rock. This process creates ions, or electrically charged atomic particles. These ions are carried away in run off to streams and rivers and ultimately to the ocean.
(iv) Many of the dissolved ions are used by organisms in the ocean and are removed from the water. Others are not used up and are left for long periods of time where their concentrations increase over time.
(v) Two of the most prevalent ions in seawater are chloride and sodium. Together, they make up over 90 percent of all dissolved ions in the ocean. Sodium and Chloride are 'salty'. So, the oceans are salty