GEOGRAPHY OCEAN The oceans and seas occupy about 71 per cent of the total earth surface which means that about 29 percent of the earth s surface is occupied by the land. The study of the oceans. The water in the oceans, the movement of water and the economic significance of the ocean is called oceanography. The ocean basins of the world are large depressions on the earth s surface which are filled by a great mass of salt water. TYPES OF OCEANS There are four major types of oceans in the world and the rest constitution the seas 1. Pacific ocean which occupies 165 mill km 2 2. Atlantic ocean which occupies 82 mill km 2 3. Indian ocean which occupies 74 mill km 2 4. Arctic ocean which occupies 14 mill km 2 5. The seas which occupies 25 mill km 2 Economics Importance of Oceans to Man 1. Means of transportation 2. Provision of food 3. Provision of employment 4. Tourism 5. Development of seaports 6. Promotion of economic activities 7. Extraction of salts 8. Sources of minerals 9. Provision of industrial products 10. Educational research 11. Influence climate adjoining the coastlands 12. Source of sea weeds Relief of the ocean floor 1. Continental Shelf - These are areas of shallow water which surround the continent. The continental shelves are wider in some areas of the world such as the edges of the Arctic ocean. - It is a continuation into the sea of the coastal plain - It forms a gentle sloping flat form extending from the sea level to an average depth of about 200m - It is of varying widths which contain shallow water - It forms 7% of the total area of the ocean - It is found in Labrador Importance of Continental Shelf 1. It is a good fishing ground 2. Development of natural harbour 3. Facilitates exploration of petroleum 4. they are tourist centres 2. Continental Slope - Is the continuation of continental shelf into the ocean floor - The continental slope links the continental shelf with the deep sea plain or ocean floor - It is narrow and deep
- It drops in depth to about 400 metres 3. Ocean Ridge The ocean ridges take the form of either a ridge on a plateau 1. Ocean ridge takes the form of either a ridge or a plateau 2. It rises up from the deep sea plain 3. Some rise above the surface to form oceanic islands 4. Deep Sea Plain These are wide, gently undulating or fairly level surfaces which have a depth of between 2000m and 3000m - This is a wide gently, undulating or fairly level surface - It has a depth of between 2000m and 2000m - It occupies 3 2 of the ocean floor - It is also called the Abyssal plain OCEAN DEEP These are very deep trenches in the floor of the ocean - These are the long, narrow trenches that plung as great ocean deeps - They are of about 9000 metres in depth Manana trench - Materials, mainly deposited on the ocean floor include i. oozes ii. Clay iii. Muds Salinity of the Ocean DIAGRAM Diagram should be provided by the teacher Salinity is defined as the degree of saltiness or concentration of salt solution in oceans and seas. The degree of salinity varies from ocean to ocean and it is measured in percentage or per thousand. Factors Affecting Salinity of Ocean The salinity of ocean is determined by the following factors. 1. The amount of fresh water added to the ocean. Fresh water is derives from rain, rivers, streams and melting ice. The more the volume of water added to the ocean, the lower the degree of saltiness and vice versa. 2. The degree of water mixing with ocean currents: within the enclosed water bodies such as the red sea the salinity is very high because of the absence of ocean current mixing with it. Whereas in seas that are not enclosed the degree of their mixing with ocean current is very high therefore there is reduction in salinity.
3. The rate of evaporation: The higher the rate of evaporation the higher the salinity of the ocean and vice versa. In tropics the higher the rate of evaporation in the ocean water the higher the salinity whereas in the arctic the lower the evaporation of the ocean water the lower the salinity. Ocean currents Ocean currents simply refer to the regular movement of large masses of surface water from one part of ocean to another. Types of Ocean Current Ocean currents can be grouped into two main types 1. Warm ocean currents 2. Cold ocean currents 1. Warm Ocean Currents: are those that flow from the equatorial regions towards the poles with a relatively high surface temperature 2. Cold Ocean Currents: are those current that flow from the poles towards the equatorial region with a relatively low temperature Causes of Ocean Currents 1. The rotation of the earth 2. Planetary winds 3. The temperature differences 4. Salinity 5. The slope of the landmass Effects of Ocean Currents on Adjacent Coastlands 1. Ocean currents modify the climate of an area by raising the temperature when cold and warm 2. The various warm currents of the ocean bring regular rainfall to their coastland 3. Cold currents bring about coastal fogs instead of actual rain and this is responsible for poor visibility which passes danger to sailors on the high sea and aeroplane. 4. Cold currents bring about reduction in temperature through the formation of coastal fogs 5. Cold currents and aridity of the landmass which they blow across 6. In polar regions, warm currents enhance ports to be free from ice 7. The meeting of warm and cold currents encourages the formation of plankton which is an essential food for fish Distribution of Ocean Currents according to their Hemisphere 1. Northern hemisphere 1. The main warm ocean currents are
(a) Atlantic ocean - Cayen current - Florida current - Culf stream current - North Atlantic Drift - (Guinea current) - Kuroshio current - Oyashio Bering current - North pacific drift The main cold ocean current are: (a) Atlantic Ocean - Labrador current - Irminger current - Canaries current (b) - California current - Okhotsk current 2. Southern Hemisphere i. The main warm ocean currents are: Atlantic ocean - Braziham current - South Atlantic Drift - East Australian Current - South Pacific Drift Indian Ocean - Mozambique current - South Indian Ocean Drift The Main Cold Ocean Current Atlantic Ocean - Benguella current - Falkland current Indian Ocean - West Australian current
- Peruvian current