MOVEMENTS OF OCEAN WATER

The ocean water is dynamic. The horizontal and vertical motions are common in ocean water bodies. The horizontal motion refers to the ocean currents and waves. The vertical motion refers to tides.

WAVES

Waves are actually the energy, not the water as such, which moves across the ocean surface.

Water particles only travel in a small circle as a wave passes.

Wind provid

es energy to the waves.

CHARACTERISTICS OF WAVES

Wave crest and trough : The highest and lowest points of a wave

Wave height : vertical distance from the bottom of a trough to the top of a crest

Wave amplitude : one-half of the wave height.

Wave period : the time interval between two successive wave crests or troughs as they pass a fixed point.

Wavelength : the horizontal distance between two successive crests.

Wave speed : the rate at which the wave moves through the water, and is measured in knots.

Wave frequency : the number of waves passing a given point during a one second time interval.

TIDES

The periodical rise and fall of the sea level, once

or twice a day, mainly due to the attraction of

the sun and the moon, is called a tide.

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FORCES THAT CAUSES TIDES

1. Gravitational pull of the sun and the moon:
2. Centrifugal force

TYPES OF TIDES

Tides based on Frequency

Semi-diurnal tide : featuring two high tides and two low tides each day. The successive high or low tides are approximately of the same height.

Diurnal tide : one high tide and one low tide during each day. The successive high or low tides are approximately of the same height.

Mixed tide : Tides having variations in height

TIDES BASED ON THE SUN, MOON AND THE EARTH�POSITIONS

Spring tides : When the sun, the moon and the earth are in a straight line, the height of the tide will be higher. These are called spring tides

Neap tides : When the sun and moon are at right angles to each other, the forces of the sun and moon tend to counteract one another and causes Neap Tide.

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CONT…..

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Perigee tide: when the moon’s orbit is closest to the earth (perigee), unusually high and low tides occur.

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Apogee tide: when the moon is farthest from earth (apogee), the moon’s gravitational force is limited and the tidal ranges are less than their average heights.

CONT……

Perihelion tide: When the earth is closest to the sun (perihelion), around 3rd January each year, tidal ranges are also much greater

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Aphelion tide: When the earth is farthest from the sun (aphelion), around 4th July each year, tidal ranges are much less than average

IMPORTANCE OF TIDES

• Tide helps the navigators and fishermen plan their activities.
• Tidal flows are of great importance in navigation.
• Tidal heights are very important, especially harbours near rivers and within estuaries having shallow ‘bars’ at the entrance, which prevent ships and boats from entering into the harbour.
• Helpful in desilting the sediments and in removing polluted water from river estuaries
• Tides are used to generate electrical power

OCEAN CURRENTS

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Ocean currents are like river flow in oceans.

They represent a regular volume of water in a

definite path and direction

FORCES INFLUENCING OCEAN CURRENT

1. Primary forces:

• heating by solar energy
• Wind
• Gravity
• Coriolis force

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2. Secondary forces:

• Water Density
• Water Salinity
• Water Temperature

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TYPES OF OCEAN CURRENTS

On the basis of depth:

(i)surface currents: constitute about 10 per cent of all the water in the ocean, these waters are the upper 400 m of the ocean

(ii) deep water currents: make up the other 90 per cent of the ocean water. These waters move around the ocean basins due to variations in the density and gravity

ON THE BASIS OF TEMPERATURE

(i) cold currents: bring cold water into warm water areas.

Usually found on the west coast of the continents

in the low and middle and on the east coast in the

higher latitudes in the Northern Hemisphere

(ii) warm currents: bring warm water into cold water areas.

Usually observed on the east coast of continents in

the low and middle latitudes. In the northern

hemisphere they are found on the west coasts of

continents in high latitudes

MAJOR OCEAN CURRENTS

EFFECTS OF OCEAN CURRENTS

1. It regulates the global temperature. It gives free navigation.

The north eastern arm of Gulf Stream keeps ports & harbours of Russia & Scandinavia navigable through out the year.

2. It distributes minerals & pollution added to it becomes highly diluted & later negligible.

3. It helps in growth of juveniles of certain fish & its distribution to other countries - from its place of origin.

4. It allows sustenance of plankton & subsequent fish population - for e.g Anchovetta forms the largest fish landings due to Benegula current.

5. The Kuroshio current makes ports on Japan navigable during winter.

6. Some up wellings & down wellings are due to currents which bring minerals to photic zone used by phytoplankton.

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