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OCEAN CURRENTS
-The knowledge of major surface currents comes principally from compilation of mariner’s observation begun in 1840 by the American oceanographer, Mathew Fontanel Maury. It was discovered that, ships courses, are deflected by surface currents. The currents cause discrepancy between ships intended position, and its actual position after it has traveled for a period. With this it was once discovered that, sea surface water have currents. Therefore ocean currents defined as are the movements of surface water masses in the ocean in the ocean basin horizontally covering a considerable distance.
There are two types of ocean currents namely cold and warm currents.
-The cold ocean currents in the world includes; Peruvia, California, West wind drift, Benguela, Canaries, South pacific current, south Atlantic current, south equatorial and Oyashi.
-The warm ocean currents includes; North equatorial currents, North Atlantic drift, North pacific current, Kuro siwo, Mozambique, South Equatorial current, Brazil and Others. The ocean current is produced by the combined factors which are also considered as interplay factors for ocean currents. These include the followings.
1.The world wind belts the blow of global wind systems over oceans, set up the surface water in motion and thus produce currents. Moreover the directions taken by the wind blow.
2.The temperature of the ocean water the ocean waters temperature of region produce either cold and warm currents. Cold currents develop in Polar Regions, while the warm currents develop in areas of tropical latitudes.
In Polar Regions the average temperature is around 4
and sometimes is much lower. The water is therefore cooled, descends and moves towards the Equator at great depths in the oceans. In tropical regions where the average water temperature is around 26, the water is heated and expand. Hence ocean water moves away from the area at shallow depth towards the polar.
and sometimes is much lower. The water is therefore cooled, descends and moves towards the Equator at great depths in the oceans. In tropical regions where the average water temperature is around 26, the water is heated and expand. Hence ocean water moves away from the area at shallow depth towards the polar.3.The rotation of the earth; The rotation of the earth exert the force on the earth’s surface which deflects the movements of objects from their normal position to the right in the northern hemisphere and to the left in southern hemisphere. Hence the movements of ocean water surface are also deflected to the right and to the left in the northern and southern hemisphere respectively.
4.The shape of land masses; The shape(angle)of the coastline affect the direction of water current by redirecting it in certain path. Hence the path taken in any particularly current partly depends on the shape of coastline.
SEA LEVEL CHANGE
Sea level change is defined as a variation in the general level of the sea. The average position of the sea in relation to the land has remained relatively constant for the nearly 6,000 years. Before that time, there are had been several changes in the mean sea level. The most dramatic change being as a result of the quaternary ice and plates movement.
Sea level refers to a general level of the sea as if it were influenced by tides of waves.
Sea level refers to a general level of the sea as if it were influenced by tides of waves.
Sea level changes in classified into
- Negative changes (negative movements) in which the sea level is falling relative to land level. The coastal land emerges.
- Positive changes (positive movements) in which the sea level is rising relative to the land level. The coastal land subsides.
Causes of the sea level changes.
1) Glacial formation and melting of ice.
2) The rising and falling of coastal land i.e. Isostatic movements.
3) Eustatic change can also be caused by the change in the size of the ocean basin.
Coastal Scenery resulting from changes in the sea level
Relative move of the sea level can be grouped into negative and positive as mentioned earlier .
-Negative movement produce Emerged coasts
-Positive movements produce submerged coasts
1. SUBMERGED COASTS
-Occurs when highland along/near the coast lines become submerged (sinking of the land).
a) RIA coast
This is the coast which is formed when the highland area with level valleys is submerged and the lower parts of its river valley becomes flooded by water from the sea. The submerged river valleys are called rias, formations of harbors. E.g. Between Sierra Leone and Gambia, coast of guinea Bissau West Africa. Mombasa and Dar coast (harbors)
b) Fiord coast
This is formed when glaciated U-shaped valley are flooded after the submergence of former coastal highland. The flooded glaciated U-shaped valleys are called fiords. E.g. Alaska in U.S.A, South island in New Zealand, Fiord in Chile.
c) Dalmatian/longitudinal coasts
-Coasts formed/found in regions made up of hills and valleys which lie parallel to the coast are submerged. After submerged; – The valleys which are between the mountains are flooded. The flooded valleys are called sounds and mountain ranges become chains of island E.g. Dalmatian coast in Yugoslavia.
Submerged coast in lowland
a) Estuarine coast –flooded parts of river valley at their mouth.
-Formed when the lowland area along the former coast is submerged due to penetration of water inland after the rise sea level. The submergence leads to the formation of the feature like estuaries. Estuaries coast are formed when the river mouth is drowned.
-Formed when the lowland area along the former coast is submerged due to penetration of water inland after the rise sea level. The submergence leads to the formation of the feature like estuaries. Estuaries coast are formed when the river mouth is drowned.
2. EMERGENT COAST
-Form when the lands under water (continental shelves) become dry land by uplift. /formed where there is a relative fall in the sea level leads to emergence of larger part.
Emergent upland (of the continental shelf)
i) Raised beaches – These are the beaches which stand above the present shore line.eg in Mombasa
ii)Wave – Cut Platform:
-These are platform like features standing above the present shoreline.
iii)Notches:
-These are v- shaped cut formed as of undercutting of a cliff during the high tide on the emerged coast.
iv)Old Cliff:
-Is the cliff which stands above the next cliff.
-These are platform like features standing above the present shoreline.
iii)Notches:
-These are v- shaped cut formed as of undercutting of a cliff during the high tide on the emerged coast.
iv)Old Cliff:
-Is the cliff which stands above the next cliff.
ACCORDING TO STRUCTURE TREND OF LAND
i. CONCORDANT COAST
-Type of coast where by the structure trend of the land is parallel to the coast, in this the highland like mountain and valleys run parallel the direction of the coastal alignment e.g. Dalmatian of Yugoslavia.
ii. DISCORDANT COAST
-Type of coastal where by the structure trend of land is at height angle top the coast. It is mountain and valley running at right angle to coast. Example fiord coast in the Scandinavian
Classification of sea level changes.
- Sea level change is classified into two basic types according to the causal factors influenced it to occur and include.
i. Eustatic Sea levels change
It is the variation in the general level of the sea taking place at a global level (worldwide) usually caused by either melting of ice or severe freezing of water. Severe freezing of water causes the rise in sea level as more water discharged into the ocean basin.
ii. Isostatic sea level change
-It is the local variation of the sea level caused by he changes in the level of land as a result of earth’s movement. When land rises, sea level falls, and when the land level falls sea level rises.
- Sea level change is also classified as positive and negative change:
Negative change is the fall of the sea level relati
vely to the land level while
positive change means the rise of the sea level
vely to the land level while
positive change means the rise of the sea level
EVIDENCES INDICATING THE PAST CHANGE OF THE SEA LEVEL.
1. GEOMORPHOLOGY EVIDENCES
The geomorphology evidences are principally to the features related to submerged and emerged coasts resulting from the rise and fall of the sea level relatively to land level.
The features associated with the submerged coasts include the following:-
(i). Estuarine coast.
It is a low lying coastline with a fully flooded river valley. The feature is produced as the low lying coastline with river valley submerged following the rise of the sea level making the valley of the river fully flooded by the oceanic water.
Where estuarine coast found, it becomes difficult to recognize the levels of the river and sea. The most classic example of estuarine coast in the world is that of Thames coast in England
(ii). Ria coast.
It is highland coastline with a partially flooded river valley. It results where a coastline of high level with river valley submerged as sea level rises making of rises making the lower parts of the valley flooded. Ria coasts are common in SW Ireland, SW England and New Spain
(iii) Longitudinal coast.
It is a coastline lies parallel to the submerged valleys of mountain chain.
Where highland coast whose mountain valleys parallel to the coast, after submergence, the valleys will be flooded and the mountains separating the valleys, become chains of island. A good example of Dalmatian coast, is the coast of Yugoslavia
(iv) Fiords.
Fiord is a long narrow steeply sided and deep sea inlet along the coast. A coast line with this unique feature, is called fiord coast. Fiords were produced by the drowning of glacial troughs after submergence. A good example of fiord is that of also in Norway
The features associated with emerged coastlines include the following
(i) Offshore features like beaches
These were produced after the low land coast to have been emerged. The emerge of the coast makes the features which were along the shore line to appear out of the shoreline as a new shore line formed. Off features are more observed along the Gulf of Mexico.
(ii) Raised features
The features which appear high enough away from the sea. These have resulted after the high land coast to have been emerged. These include mostly the raised beaches. E.g. Raised beach in western Scotland.
2. ARCHEOLOGICAL EVIDENCE
It is much based on Neolithic settlements and Roman pavements in the Southern Sweden, which appear below the present low tide mark.
3. ROTANIC EVIDENCE
It is principally to the finding of peat, formed due to the submergence of forests on the coast of Wirral peninsula nearly Harleth in North Wales.
4. REJUVENATION OF RIVERS AT LOWER COURSE
Most of the rivers at lower courses characterized by having gentle or general level gradient giving to low water velocity. Some rivers have high water velocity which indicates that, the gradient of water flow has increased due to the fall of sea level relatively to the coast land.
LIFE IN THE OCEAN
Ocean water supports the life of organisms because of its aquatic eminent. The aquatic environments provide organisms with important gases nutrients, food and other important requirements
The organisms found in marine water are of both, plants and animals
Organisms in the marine aquatic ecosystems are of married nature, and also have varied habits. By being varied in such aspects, organisms broadly categorized into the following forms.
According to their habits, marine organisms include the following groups
a. Benthos
These are the organisms living on or in the ocean bottom (benthic environment) some live on bottom sediments. And called in fauna. And others live near bottom water called epifauna. Examples of benthos include; marine warms, mollusks, crustacean, star fish and others. Generally speaking, benthic organism is far more abundant in shallow water than on the deep ocean bottom.
b. Nektons
These are the free swimming animals, they are more abundant in near surface waters, but occur at all depths in the ocean. Many types of nekton organism have regular daily vertical migration, At night they swim to the surface water to feed up on the abundant life in this layer. During the day they return to greater depth where they are more difficult to be seen and less likely to be eaten
Some common nektonic organisms
c.Neutrons
These are the marine organism live at the upper surface layer of the sea. Some live on the water surface, and others live just below the ocean surface neutrons include, Valella, physalia and other related forms of organisms
c. Neutrons
Marine organism according to their varied nature include the following.
1. Plankton
These are the minute pelagic plants and animals that are weak swimmers and can easily moved by currents. Plankton are further divided into:-
(a) Phytoplankton(plant plankton)
There are the minute single called plants. They live nearly to surface in the environment called euphoric zone, because of requiring sufficient sunlight for photosynthesis,
(b) Zooplanktons, (Animal plankton)
These are the animal plankton in the marine ecosystem.
2. Marine mammals.
Marine mammals include: Whales, dolphins, seals, sea lions and others. They are warm boded, breath air and give live birth to their young. These are legless and have streamlined bodies.
3. Sea birds
Sea birds are among of conspicuous and familiar form of marine life. Some spend nearly their entire life in the sea, others can barely walk on land, Some sea birds only use seawater for food. Some fly over the seawater and other swim under water
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