Movements of Ocean Water Notes in English Class 11 Geography Chapter-13 Book-Fundamental of Physical Geography

 

ocean water

• Water does not remain still, it is always moving. 

• Its motion is caused by its physical characteristics (such as temperature, salinity, density) and external forces (such as the Sun, Moon and wind). 

• There are two types of motion in water - horizontal and vertical. Currents and waves are associated with horizontal motion, while tides are an example of vertical motion. 

• Currents move large amounts of water in one direction, while waves only cause disturbance on the surface of the water. In vertical motion, water moves up and down, influenced by the attraction of the sun and moon.

Waves

Waves in the sea are not water but energy that moves here and there on the surface. This energy is created due to the wind and ends when it reaches the shore.

How are waves formed?

• Effect of wind:  Wind imparts energy to water, creating ocean waves. The faster the wind speed, the bigger and more powerful the waves become.

• Water motion:  Water particles move around in circles with the waves, but the intensity of this effect is greatly reduced in deep water.

• Waves on the shore:  When the waves reach the shore, their speed slows down. As the depth decreases, the waves lose their balance and break into white foam.

features of waves

• Wave size:  The size of waves indicates their origin. Waves created by strong winds are high and sharp, while waves coming from distant places are low and more regular.

• Movement of waves:  The wind pushes the water forward, while the force of gravity pulls it back. In this process, the movement of water is circular, in which it moves up and down and back and forth.

• Small and big waves:  Small waves are formed by low air pressure.  And big waves are formed far away in the ocean and travel thousands of kilometers. 

• White foam and breaking waves:  As they approach the shore, the waves slow down, lose balance and break, creating white foam or surf.

tide

Tides are the periodic rise and fall of ocean water caused by the gravitational force of the moon and sun. They happen once or twice a day and have a big impact on the sea floor.

How are tides formed?

1. The main reason

• Moon's gravity: The moon pulls Earth's water toward it, causing tides (bulges).

• Centrifugal force: This force pushes water away from the Moon on the other side of the Earth, creating tides there too.

2. Balance of gravity and centrifugal force

• The gravitational force of the moon is more effective on the side near the moon, while the centrifugal force is more effective on the side of the Earth away from the moon. As a result of these two forces, two tidal bulges are formed on the Earth.

factors affecting tides

• Continental Coasts:  Tide height is high on broad coasts.

• Bays and estuaries:  Conical bays increase the intensity of the tides.

• Mid-ocean islands:  Collision with these causes change in the height of the tide.

Surge and Tidal Current

• Surge: Unstable water movement in the ocean caused by the effects of climate (wind and pressure).

• Tidal Current: When the tides pass through bays, rivers or between islands.

Impacts in coastal areas

• Tides have a profound influence on coastal activities and maritime transport, particularly in narrow bays or estuaries, where their effects are more clearly visible.

Types of tides

Tides are divided into different types based on their frequency (how often they occur), direction and change in speed. They are mainly classified on two basis:

• How many times does the tide occur in 24 hours?

• How high does the tide rise?

Tides based on frequency

Tides are the cycles of rising and falling of water in the ocean, which are caused by the gravitational force of the Sun, Moon and Earth. It is divided into different types based on frequency.

• Semi-diurnal Tide:  This is the most common type of tide, in which there are two high tides and two low tides every day. The height of both these high and low tides is almost the same.

• Diurnal Tide:  In this type of tide there is only one high tide and one low tide in a day, and the height of both the tides is the same.

• Mixed Tide:  These types of tides vary in height. These tides are usually seen on the west coast of North America and the islands of the Pacific Ocean.

Tides based on the position of the Sun, Moon and Earth

• Spring Tide:  When the Sun, Moon and Earth are in a straight line, the highest tides are produced, which are called spring tides. This phenomenon occurs twice a month, at the time of new moon and full moon.

• Neap Tide:  When the Sun and Moon are at right angles to each other, the height of the tide decreases, which is called neap tide. This phenomenon occurs 7 days after the high tide.

Effect of the distance between the Moon and the Sun

• When the Moon is close to the Earth (perigee):  Unusually high and deep tides occur.

• When the Moon is at a greater distance (apogee):  the height of the tide is lower than normal.

• When close to the Sun (Perihelion):  Being close to the Sun in January increases the effect of tides.

• When away from the Sun (Apseer):  In July, the effect of tides reduces due to distance from the Sun.

position between tides

• Ebb is the situation when the water level falls, while flood tide is the situation when the water level rises.

Importance of tides

Tide is the cycle of rise and fall of water in the ocean, which helps in many important functions.

• Aids navigation:  Tide forecasting helps sailors and fishermen plan their voyages. The height of the tide is important for ships to enter rivers and coastal areas. In addition, tidal flows provide passage for boats in shallow areas.

• Desiltation:  Tides help in cleaning the sediment deposited in rivers and estuaries. It also plays an important role in draining polluted water out into the sea.

• Electricity generation:  Tides are used to generate electricity. Tidal power plants are operating successfully in countries like Canada, France, Russia and China. In India too, a 3 MW tidal power plant is being set up at Durgaduwani in the Sundarbans region of West Bengal.

Ocean Currents

Ocean currents are the regular flow of water in the ocean, which, like rivers, flow in a certain direction in the oceans. These currents are driven by natural forces.

Forces affecting currents

Ocean currents are driven mainly by primary and secondary forces. 

• Primary  forces:   Primary forces include the sun's heat, wind, and gravity. Solar energy heats water and expands, causing water to flow. Wind blowing on the surface pushes the water forward, and gravity creates a pressure difference, pulling the water down. The Coriolis force deflects currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, creating circular flows (such as rings or gyres) in the oceans. 

• Secondary force:  Secondary force depends on the difference in water density. Colder and saltier water, being heavier, settles down, while warmer and lighter water rises, which controls the flow of currents.

cycle of warm and cold currents

• Warm currents flow along the surface from the equator towards the poles and replace cold water. On the other hand, cold currents settle down from the polar regions and flow towards the equator.

Importance of Ocean Currents

• Ocean currents play a vital role in balancing warm and cold water. They not only regulate ocean temperatures but also deeply influence marine life and global climate.

Types of ocean currents

Ocean currents are divided into different categories based on their depth and temperature.

Based on the depth

• Surface Currents:  About 10% of the ocean water is in the form of surface currents, which flow from the ocean surface to a depth of up to 400 meters. These currents are driven mainly by wind and solar energy.

• Deep Water Currents:  About 90% of the ocean water is in the form of deep currents, which are formed mainly due to density and gravity. In areas with cold and dense water, such as polar regions, the water becomes heavier and settles down and gives rise to deep currents.

Depending on the temperature

• Cold Currents:  Cold currents balance ocean temperatures by bringing cold water to warmer regions. These currents usually flow on the western coasts of continents. For example, in the Northern Hemisphere, cold currents are found on the eastern coasts of high latitude regions.

• Warm Currents:  Warm currents balance the temperature by bringing warm water to cold areas. They mostly flow on the eastern coasts of continents. For example, in the Northern Hemisphere these currents are found on the western coasts of high latitude areas.

Major ocean currents

Ocean currents are the regular movements of water in the oceans, influenced primarily by prevailing winds and the Coriolis effect. These currents work in a similar way to atmospheric currents.

• Flow of ocean currents:  The flow of ocean currents depends on atmospheric conditions and the Coriolis effect. The currents follow the flow of air anticyclones in the middle latitudes and cyclones in the high latitudes. Monsoon winds change the direction of the currents. The Coriolis effect causes the currents to turn to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

• Contribution of warm and cold currents:  Warm currents transport heat from warm regions towards the poles, while cold currents carry cold water from polar regions towards the tropical regions, thus maintaining the temperature balance.

• Effects of ocean currents:  Ocean currents affect the Earth's climate, environment and human activities directly and indirectly. These currents create a natural balance by moving ocean water to warm and cold areas.

• Effect of ocean currents on climate: Cold currents flow on the western coasts of continents in tropical and subtropical regions, which reduces temperature and temperature difference. Fog forms here, but the atmosphere remains dry. Warm currents flow on the western coasts of continents in middle and high latitudes, which makes the weather mild in winter and less hot in summer. Warm currents on the eastern coasts of continents meet in tropical regions, which makes the climate hot, humid and increases rainfall.

• Contribution to fisheries:  Where warm and cold currents meet, the amount of oxygen in the water increases, which creates a favorable environment for the growth of plankton (the main food of fish). This is why the world's major fishing areas are located at the confluence of these currents.