Class 11 Geography chapter 13 movement of ocean water notes

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 Movement of ocean water 

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The ocean water is dynamic the horizontal and vertical motions are common in ocean water bodies

Horizontal 

• Refers to ocean currents and waves 
• Ocean currents are the continuous flow of huge water in a definite direction 
• Waves are the horizontal motion of water

Vertical 

• Refers to tides

• Vertical motions refer to the rise and fall of water due to attraction of the sun and the moon

Waves

• The water in waves does not move only the wave trains moves ahead 
• Waves are actually the energy which moves across the ocean surface 
• Wind provides energy to waves
•  the energy is released on shorelines
• When a wave approaches the beach it slow down this is due to the friction occurring between the dynamic water and the sea floor 
• This is also when the debt of water is less than half of the wavelength of the wave the wave breaks
• Waves continue to grow larger as the move and absorb energy from the wind

Most ocean waves are created by the wind pushing against the water. 

• Small Ripples: When the wind blows gently at two knots or less, tiny ripples form on the calm water.
• Growing Waves: As the wind becomes stronger, these ripples grow into bigger waves. Eventually, they break at the top, creating white foam called white caps.
• Journey Across the Ocean: Waves can travel thousands of kilometers across the ocean before they reach the shore, where they break into surf.

What Waves Tell Us

• The size and shape of a wave reveal its origin:
• Steep Waves: These are younger waves, likely created by nearby winds.
• Smooth, Steady Waves: These come from far-off places, possibly even another hemisphere.
• The biggest waves are formed by strong winds blowing over a large area for a long time in the same direction.

How Waves Move

• Waves move because the wind pushes the water, while gravity pulls the wave crests down. This movement causes water to circle, creating a pattern:
• The water moves up and forward as the wave approaches.
• It moves down and back as the wave passes.

Key Features of Waves

• Here are some simple terms to understand waves better:
• Crest and Trough: The crest is the wave’s highest point, and the trough is its lowest point.
• Wave Height: The vertical distance from the bottom of the trough to the top of the crest.
• Wave Amplitude: Half of the wave height.
• Wave Period: The time it takes for two crests (or troughs) to pass a fixed point.
• Wavelength: The distance between two crests.
• Wave Speed: How fast the wave moves, measured in knots.
• Wave Frequency: The number of waves passing a point in one second.
  
  
  

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 
• Moment of water caused by meteorological effects ( wind and atmospheric pressure changes ) are called surges. They are not regular as tide

Factors 

• The moon’s gravitational pull to large extent 
• the suns gravitational pull to a lesser extent
• Another factor is centrifugal force which is the force that acts to counter balance the gravity 
• Together they both are responsible for creating two major tidal bulges on the earth
• Tides are caused by a balance between two forces:
• 1. The Moon’s Gravity: The moon pulls on the Earth’s water with its gravitational force.
• 2. Centrifugal Force: This is the outward force caused by the Earth and moon spinning around their shared center of gravity.

How Tidal Bulges Form

• Closer to the Moon: On the side of Earth facing the moon, the moon’s gravitational pull is stronger than the centrifugal force. This creates a bulge of water towards the moon.
• Farther from the Moon: On the opposite side of Earth, the moon’s gravity is weaker, and the centrifugal force dominates. This causes a second bulge of water, away from the moon.
• These bulges are what we recognize as high tides.

Factors That Affect Tides

• 1. Continental Shelves: In wide, shallow areas, tidal bulges are taller.
• 2. Mid-Ocean Islands: When tides reach islands in the middle of the ocean, they tend to be lower.
• 3. Bays and Estuaries: The shape of the coastline can magnify tides. For example, funnel-shaped bays make tides stronger.
  
  
  

Tidal Currents

• When water is forced through narrow areas, like between islands or into bays and estuaries, it creates tidal currents—strong flows of water caused by changing tides.

The Tides of Bay of Fundy

• The Bay of Fundy in Nova Scotia, Canada, experiences the highest tides in the world, with water levels rising up to 15-16 meters. This dramatic change occurs twice daily, with two high tides and two low tides roughly every 24 hours.
• Speed of the Tide: Since the tide rises within about six hours, it increases by approximately 240 cm per hour.
• Safety Tip: On beaches with steep cliffs (common in the area), it’s crucial to monitor the tides. A rising tide could quickly cover large areas and become dangerous.

Types of tides 

Types of Tides Based on Frequency

• 1. Semi-Diurnal Tide:
• The most common type.
• Two high tides and two low tides daily, with heights approximately equal.
• 2. Diurnal Tide:
• One high tide and one low tide each day.
• Heights are consistent.
• 3. Mixed Tide:
• Uneven heights in successive high and low tides.
• Found along the west coast of North America and in parts of the Pacific Ocean.

Based on the Sun, Moon, and Earth Positions

• 1. Spring Tides:
• Occur when the sun, moon, and Earth align (during full moon and new moon).
• Result in the highest tides due to combined gravitational forces.
• 2. Neap Tides:
• Occur when the sun and moon form a right angle with Earth.
• The gravitational forces partially cancel each other out, creating lower high tides and higher low tides.
  
  
  

Special Cases

• Perigee Tides: When the moon is closest to Earth, causing unusually high and low tides.
• Apogee Tides: When the moon is farthest from Earth, resulting in smaller tidal ranges.
• Perihelion Tides: Around January 3rd, when Earth is closest to the sun, causing greater tidal ranges.
• Aphelion Tides: Around July 4th, when Earth is farthest from the sun, causing smaller tidal ranges.

Key Terms

• Ebb: The period when the water level is falling (from high tide to low tide).
• Flow/Flood: The period when the tide is rising (from low tide to high tide)

Importance of tides 

•  Predictability: Tides are influenced by predictable Earth-moon-sun positions, helping navigators and fishermen plan effectively.
• Navigation: Tidal flows assist in navigation, especially in shallow estuaries or harbors.
• Environmental Benefits: Tides help remove sediments and polluted water from river estuaries.
• Energy Generation: Tidal power plants in countries like Canada, France, Russia, and China generate electricity. In India, a 3 MW tidal project is under development in the Sundarbans. 
• Tides are not just natural phenomena but vital for ecosystems, navigation, and renewable energy!

Ocean currents 

• Ocean currents are like rivers within the ocean, flowing in regular paths and directions. They result from a combination of forces that initiate movement and influence the flow.

Forces Influencing Ocean Currents

• Primary Forces (Start the currents):

•  Solar Heating:

• The sun heats water near the equator, causing it to expand.
• This expansion makes sea levels near the equator about 8 cm higher than in middle latitudes, creating a slight slope for water to flow downhill.

• Wind:

• Wind blowing over the ocean’s surface creates friction and pushes water, generating surface currents.

•  Gravity:

• Gravity pulls water down from higher levels, maintaining the slope-driven flow.

•  Coriolis Force:

• Due to Earth’s rotation, currents are deflected to the right in the Northern Hemisphere and the left in the Southern Hemisphere.
• This deflection creates large circular current systems known as Gyres, found in ocean basins worldwide.

• Secondary Forces (Control depth and direction):

• Water Density Differences:

• Cold, salty water is denser and sinks, while warm, less salty water is lighter and rises.
• This movement contributes to vertical currents and the overall flow of ocean water.
  
  
  

Types of Ocean Currents

Based on density 

The ocean currents may be classified based on their depth as surface currents and deep water

currents : 

(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. 

 Based on Temperature

Ocean currents are classified into two main types based on their temperature: cold currents and warm currents. These currents play a vital role in regulating the Earth's climate, influencing marine ecosystems, and shaping coastal environments.

1. Cold Ocean Currents

Definition: Cold currents carry cold water from polar or high-latitude regions to warmer areas.

Characteristics:

• Found along the west coasts of continents in low and middle latitudes in both hemispheres.
• Located on the east coasts of continents in higher latitudes of the Northern Hemisphere.

2. Warm Ocean Currents

Definition: Warm currents carry warm water from equatorial regions to cooler areas.

Characteristics:

• Found along the east coasts of continents in low and middle latitudes in both hemispheres.
• Located on the west coasts of continents in higher latitudes of the Northern Hemisphere.

Effects of ocean currents 

Climate Impacts

1. West Coasts in Tropical and Subtropical Regions:

• These coasts are bordered by cool currents, leading to:

•  Lower average temperatures.
• Narrow temperature ranges (both daily and annually).
• Frequent fog
• Generally arid conditions

2. West Coasts in Middle and Higher Latitudes:

• Bordered by warm currents, creating a marine climate characterized by:
• Cool summers and mild winters.
• Narrow annual temperature ranges.

3. East Coasts in Tropical and Subtropical Regions:

• Warm currents flow along these coasts, resulting in:.
• Warm and rainy climates.
• These areas typically lie in the western margins of subtropical anti-cyclones, which further influences rainfall patterns.

Marine Ecosystems

• Mixing Zones of Warm and Cold Currents:

• Where warm and cold currents meet, oxygen levels increase, supporting the growth of plankton, the primary food for fish.

• These zones are home to some of the world's richest fishing grounds.

Importance of Mixing Zones

1. Marine Biodiversity:

• Enhanced oxygen and plankton growth attract a variety of fish species, making these regions biodiversity hotspots.

2. Fishing Industry:

• Areas where warm and cold currents mix, such as off the coasts of Japan and Newfoundland, are among the world's best fishing grounds, supporting local economies.

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