Movement Of Ocean Water

Ocean water is never still. It continuously moves in different forms because of wind, temperature, salinity, density, the Sun, the Moon and Earth’s rotation.

The oceans show three main types of movements:

• Waves
• Tides
• Currents

Currents and waves are mainly horizontal movements, while tides are mainly vertical movements.

Ocean currents move a huge amount of water in a definite direction. Waves mainly transfer energy across the water surface, while water particles themselves do not move forward significantly.

Waves

Waves are oscillatory movements that cause the rise and fall of ocean water at the surface.

They are formed when air and water molecules interact and wind energy is transferred to the water.

Energy passing through water causes it to move in a circular motion. As a wave passes, water particles move in small circular paths.

Waves get most of their energy from the wind.

Formation Of Waves

Wind creates waves on the ocean surface.

The energy of waves is released along the coast.

Deep bottom water is rarely affected by surface wave movement.

A wave slows down near the shore because of friction between moving water and the sea floor.

A wave breaks when the water depth becomes less than half of the wavelength.

Open oceans have the most powerful waves.

Waves continue to grow as they travel and absorb wind energy.

Their origin can be understood from their magnitude and shape.

• Steep waves are relatively new and are usually formed by local winds.
• Slow and steady waves generally come from distant regions, often from faraway storms.

Characteristics Of Waves

Wave Crest

The crest is the highest point of a wave.

Wave Trough

The trough is the lowest point of a wave.

Wave Height

Wave height is the perpendicular distance between the bottom of a trough and the top of a crest.

Wave Amplitude

Wave amplitude is half of the wave height.

Wave Period

Wave period is the time interval between two successive wave crests or troughs passing a fixed point.

Wavelength

Wavelength is the horizontal distance between two successive crests.

Wave Speed

Wave speed is the speed at which a wave travels through water.

It is generally measured in knots.

Wave Frequency

Wave frequency is the number of waves passing a fixed point in one second.

Tides

The periodic rise and fall of sea level once or twice a day is called tide.

Tides occur mainly because of the gravitational attraction of the Moon and the Sun.

The Moon has a stronger effect on tides because it is closer to the Earth.

Another force involved is centrifugal force, which counterbalances gravity.

Together, the gravitational pull of the Sun and Moon and centrifugal force create two major tidal bulges on the Earth.

Storm Surge

Movement of water caused by meteorological effects such as wind and atmospheric pressure changes is called storm surge.

Factors Affecting Tides

Tides are affected by:

• Gravitational pull of the Moon
• Gravitational pull of the Sun
• Centrifugal force
• Shape of bays and estuaries

The shape of bays and estuaries can increase tidal intensity.

Funnel-shaped bays greatly change tidal magnitude.

When tides are channelled between islands or into bays and estuaries, they are called tidal currents.

Types Of Tides Based On Rise And Fall

Flow Or Flood Tide

The time between low tide and high tide, when the tide is rising, is called flow tide or flood tide.

Ebb Tide

The time between high tide and low tide, when water level is falling, is called ebb tide.

Types Of Tides Based On Frequency

Semi-Diurnal Tide

In semi-diurnal tides, two high tides and two low tides occur each day.

Successive high and low tides are approximately equal in height.

Diurnal Tide

In diurnal tides, only one high tide and one low tide occur each day.

Successive tides are approximately equal in height.

Mixed Semi-Diurnal Tide

Mixed semi-diurnal tides show variation in tide height.

They generally occur along the west coast of North America and many islands of the Pacific Ocean.

Types Of Tides Based On Position Of Sun, Moon And Earth

Spring Tide

Spring tide occurs when the Sun, Earth and Moon lie in a straight line.

This alignment is called syzygy.

The combined gravitational forces produce the highest high tides and lowest low tides.

This creates the maximum tidal range.

Spring tides generally occur twice a month during:

• New moon
• Full moon

During new moon, the Moon lies between Earth and Sun.

During full moon, Earth lies between Sun and Moon.

Neap Tide

Neap tide occurs when the Sun and Moon are at right angles to each other.

Their gravitational forces partly cancel each other.

As a result:

• High tides are lower than average.
• Low tides are higher than average.

There is usually about a seven-day interval between spring tide and neap tide.

Magnitude Of Tides

Tides At Perihelion

Around 3 January, Earth is closest to the Sun.

The tidal range becomes slightly greater than average.

This causes comparatively higher high tides and lower low tides.

Tides At Aphelion

Around 4 July, Earth is farthest from the Sun.

The tidal range becomes slightly lower than average.

Tides At Perigee

When the Moon is closest to Earth, its gravitational pull becomes stronger.

The tidal range becomes greater than normal.

This produces higher high tides and lower low tides.

Tides At Apogee

When the Moon is farthest from Earth, its gravitational pull weakens.

The tidal range becomes lower than average.

Bay Of Fundy Tides

The highest tides in the world occur in the Bay of Fundy, Nova Scotia, Canada.

The tidal range reaches about 15–16 metres.

Because there are two high tides and two low tides each lunar day of about 24 hours 50 minutes, each tide rises or falls roughly within about 6 hours.

Oceanic Currents

Oceanic currents are like rivers flowing on the surface of oceans.

They represent the regular movement of ocean water in a definite path and direction.

Major oceanic currents are generally set in motion by:

• Prevailing winds
• Coriolis force

The pattern of ocean circulation broadly resembles atmospheric circulation.

Factors Affecting Oceanic Currents

Heating By Solar Energy

Water expands after being heated by solar energy.

Sea level near the equator is about 8 cm higher than sea level at mid-latitudes.

This creates a slight gradient, and water tends to move down the slope.

Wind

Winds blowing over the ocean surface push water in a particular direction.

Important winds affecting ocean currents are:

• Trade Winds
• Westerlies
• Monsoon Winds

Coriolis Force

Coriolis force deflects moving water:

• To the right in the Northern Hemisphere
• To the left in the Southern Hemisphere

Gravity

Gravity pulls water downward and creates gradient variations.

It also influences tides and periodic sea-level changes.

Temperature

Temperature affects ocean currents.

Currents are usually strong at the surface and weaker at greater depths.

Cold currents are formed when cold polar water sinks and moves toward the equator.

Warm currents originate near the equator and flow poleward along the surface to replace sinking cold water.

Salinity

Water with higher salinity or lower temperature becomes denser and tends to sink.

This influences vertical and horizontal circulation.

Land

Continents and islands deflect ocean currents and affect their speed and direction.

Underwater Topography

Ocean floor features such as ridges, basins and continental margins guide and redirect ocean currents.

Thermohaline Circulation

Temperature and salinity differences create water masses with specific densities.

These density differences drive deep ocean circulation at different depths.

Types Of Oceanic Currents

Ocean currents are classified on two bases:

• Depth
• Temperature

Classification Based On Depth

Surface Currents

Surface currents occur in the upper layer of the ocean, generally up to about 400 metres depth.

They are mainly driven by planetary winds such as Trade Winds and Westerlies, along with Coriolis force.

Surface currents form about 10% of total ocean water.

They play an important role in climate regulation and heat transfer.

Deep Water Currents

Deep water currents occur below the surface layer.

They form about 90% of total ocean water.

They are mainly driven by density differences caused by temperature and salinity.

They move slowly but form a continuous global circulation system called thermohaline circulation.

Classification Based On Temperature

Cold Currents

Cold currents carry water from polar or higher latitudes toward tropical or lower latitudes.

They reduce the temperature of nearby coastal areas.

Cold currents are generally found:

• On western coasts of continents in low and middle latitudes.
• On eastern coasts of continents in higher latitudes of the Northern Hemisphere.

Warm Currents

Warm currents carry water from equatorial or lower latitudes toward higher latitudes or polar regions.

They raise the temperature of nearby coastal areas.

Warm currents are generally found:

• On eastern coasts of continents in low and middle latitudes.
• On western coasts of continents in higher latitudes of the Northern Hemisphere.

Important Ocean Currents

Ocean Current	Type	Ocean
Labrador Current	Cold	Atlantic Ocean
Benguela Current	Cold	Atlantic Ocean
Brazil Current	Cold	Atlantic Ocean
Cape Horn Current	Cold	Atlantic Ocean
Falkland Current	Cold	Atlantic Ocean
South Atlantic Current	Cold	Atlantic Ocean
West Australian Current	Cold	Indian Ocean
Humboldt / Peru Current	Cold	Pacific Ocean
Kamchatka Current	Cold	Pacific Ocean
Canary Current	Cold	Atlantic Ocean
California Current	Cold	Pacific Ocean
Greenland Current	Cold	Atlantic Ocean
Oyashio Current	Cold	Pacific Ocean
West Wind Drift Current	Cold	Pacific Ocean
Somali Current	Cold	Indian Ocean
Angola Current	Warm	Atlantic Ocean
Antilles Current	Warm	Atlantic Ocean
Caribbean Current	Warm	Atlantic Ocean
Florida Current	Warm	Atlantic Ocean
North Atlantic Current	Warm	Atlantic Ocean
Agulhas Current	Warm	Indian Ocean
Leeuwin Current	Warm	Indian Ocean
Mozambique Current	Warm	Indian Ocean
Alaska Current	Warm	Pacific Ocean
Kuroshio Current	Warm	Pacific Ocean
North Pacific Current	Warm	Pacific Ocean
Gulf Stream	Warm	Atlantic Ocean
North Atlantic Drift	Warm	Atlantic Ocean
North Pacific Drift	Warm	Pacific Ocean

Ocean Mean Temperature

Ocean Mean Temperature, or OMT, is the average temperature of a specific depth of the ocean.

It is usually defined by a particular isotherm, such as the 26°C isotherm.

It is generally estimated using satellite observations along with in-situ ocean measurements.

Unlike Sea Surface Temperature, OMT is a more stable indicator of ocean thermal energy because it represents a larger volume of ocean water.

Upper ocean thermal energy strongly influences the Indian summer monsoon.

Therefore, OMT helps predict whether monsoon rainfall may be above or below the long-term average.

El Niño And La Niña

El Niño and La Niña are climatic phenomena originating in the Pacific Ocean.

They strongly influence global weather patterns.

They are part of the El Niño-Southern Oscillation, or ENSO, cycle.

ENSO includes variations in:

• Sea surface temperature
• Atmospheric pressure
• Wind systems over the tropical Pacific Ocean

The Southern Oscillation refers to periodic changes in atmospheric pressure patterns across the tropical Pacific Ocean.

La Niña

La Niña is the cooling phase of ENSO.

During La Niña, sea surface temperatures in the central and eastern Pacific Ocean fall below normal average values.

Stronger than normal trade winds push warm surface water toward the western Pacific.

This causes upwelling of cold, nutrient-rich water along the western coast of South America.

La Niña is known as the cool phase of ENSO.

It is usually associated with slightly lower global average temperatures.

It is commonly linked with:

• Stronger Indian monsoon rainfall
• Increased rainfall in Southeast Asia
• Higher frequency of Atlantic hurricanes

El Niño

El Niño is the warming phase of ENSO.

During El Niño, sea surface temperatures in the central and eastern Pacific Ocean become higher than normal.

Trade winds weaken or may reverse.

This allows warm ocean water to move eastward toward the western coast of South America.

This reduces the upwelling of cold, nutrient-rich water.

As a result, ocean surface temperature rises and atmospheric circulation patterns change.

El Niño is generally associated with higher global mean temperatures.

It commonly causes:

• Drought in India, Australia and Southeast Asia
• Heavy rainfall and floods in parts of western South America and North America

Difference Between La Niña And El Niño

Basis	El Niño	La Niña
Phase	Warm phase of ENSO	Cool phase of ENSO
Pacific temperature	Warmer-than-normal central and eastern Pacific	Cooler-than-normal central and eastern Pacific
Trade winds	Weaken or reverse	Become stronger than normal
Upwelling near South America	Reduces	Increases
Global temperature	Often increases	Often slightly decreases
Indian monsoon	Often weakens	Often strengthens

Causes Of El Niño And La Niña

The main cause of both El Niño and La Niña lies in the Southern Oscillation.

Pressure changes over the tropical Pacific affect the strength and direction of trade winds.

These wind changes affect the distribution of warm and cold ocean water.

Causes Of El Niño

• Weakening of trade winds that normally blow from east to west.
• Eastward movement of warm surface water from western Pacific to central and eastern Pacific.
• Reduction in upwelling of cold, nutrient-rich water near western South America.
• Changes in Walker circulation causing altered rainfall patterns.

Causes Of La Niña

• Strengthening of normal trade winds.
• Warm surface water is pushed further toward western Pacific.
• Enhanced upwelling of cold, nutrient-rich water near western South America.
• Lower-than-normal sea surface temperature in central and eastern Pacific.
• Strengthening of Walker circulation.

Impact Of El Niño And La Niña

The effects of El Niño and La Niña are global.

They influence:

• Weather and climate
• Agriculture
• Global temperature
• Marine life and fisheries

Impact On Weather And Climate

El Niño often causes drought conditions in India, Australia and Southeast Asia.

It may cause heavy rainfall and floods in parts of western South America and North America.

La Niña generally results in stronger monsoon rainfall in India.

It causes increased rainfall and flooding in Australia and Southeast Asia.

It may contribute to more active hurricane seasons in the Atlantic Ocean.

Impact On Agriculture

During El Niño, drought and water scarcity may cause crop failures and reduced agricultural productivity.

During La Niña, excess rainfall may damage crops.

In some regions, stronger monsoons may benefit agricultural output.

Impact On Global Temperature

El Niño events are generally associated with temporary increases in global average temperature.

La Niña events tend to produce a slight cooling effect on global climate conditions.

Impact On Marine Life And Fisheries

During El Niño, reduced upwelling causes a decline in plankton productivity and fish stocks.

This affects fishing industries.

During La Niña, enhanced upwelling supports nutrient availability, marine biodiversity and fish production.

Estuary

An estuary is a partially enclosed coastal water body where freshwater from rivers and streams mixes with saltwater from the ocean.

Estuaries and their surrounding lands are transitional zones between land and sea.

They are influenced by tides but are generally protected from the full force of ocean waves, winds and storms by surrounding landforms such as:

• Barrier islands
• Peninsulas
• Coastal ridges

Coral Reefs

Coral reefs are formed in tropical seas by coral animals.

Coral animals secrete calcium carbonate, or CaCO₃, within their skeletal structures.

When these organisms die, their calcareous skeletons accumulate and become cemented together.

This forms coralline limestone structures called coral reefs.

Conditions Required For Coral Reef Growth

Temperature

Water temperature should generally not fall below about 20°C.

That is why coral reefs are mostly found in tropical and subtropical regions.

Corals usually do not flourish along western coasts of continents where cold ocean currents dominate.

Depth Of Water

Corals normally grow in shallow water, generally within about 50 metres depth.

Sunlight must penetrate the water to support photosynthesis by symbiotic algae called zooxanthellae.

Water Quality

Seawater should be clear, saline and free from excessive sediments.

Coral reefs grow better in moving ocean waters away from muddy river mouths and sediment-rich coastal zones.

Types Of Coral Reefs

Fringing Reefs

Fringing reefs develop directly along the coastline and run almost parallel to the shore.

They are usually widest near headlands and may be absent near river mouths where sediment deposition is high.

Barrier Reefs

Barrier reefs are similar to fringing reefs but are separated from the mainland coast by a wider and deeper lagoon or channel.

Atolls

Atolls are circular or ring-shaped coral reefs enclosing a central lagoon.

They generally do not have a central landmass.

Why Coral Reefs Are Declining

Coral reefs are declining due to human-induced activities and natural environmental changes.

Major causes include:

• Climate change
• Pollution

Ocean Warming

Rising ocean temperatures, intensified by climate change and events such as El Niño, cause coral bleaching.

In bleaching, corals expel symbiotic algae called zooxanthellae.

These algae provide corals with food and colour.

Prolonged bleaching weakens corals and can cause their death.

Sea Level Rise

Rising sea level can increase sediment deposition over coral reefs.

This may smother corals and reduce sunlight penetration needed for photosynthesis.

Ocean Acidification

Higher atmospheric carbon dioxide is absorbed by ocean water.

This lowers ocean pH and increases acidity.

Ocean acidification reduces the ability of corals to build and maintain calcium carbonate skeletons.

Chemical Pollution

Agricultural runoff and industrial discharge introduce fertilizers, pesticides and toxic substances into marine waters.

These pollutants may trigger algal blooms.

Algal blooms can block sunlight and suffocate coral colonies.

Marine Debris

Plastic waste and marine litter damage coral structures physically.

They may also release harmful toxins.

Sedimentation

Coastal construction, deforestation and land clearing increase sediment runoff into the sea.

Suspended sediments increase turbidity and reduce light penetration, affecting coral growth.

Coral Bleaching

Coral bleaching is the whitening of corals due to the loss of symbiotic algae, or zooxanthellae, from their tissues.

It occurs when corals face environmental stress caused by changes in:

• Temperature
• Light intensity
• Nutrient levels

The global coral bleaching event declared in April 2024 by the National Oceanic and Atmospheric Administration was considered one of the most extensive on record.

It affected a very large proportion of the world’s coral reef ecosystems due to record-high ocean temperatures and marine heatwaves.

Causes Of Coral Bleaching

Increase In Ocean Temperature

Higher sea surface temperature linked with climate change is the primary cause of coral bleaching worldwide.

Runoff And Pollution

Heavy rainfall and runoff can reduce salinity and bring pollutants.

This stresses corals, especially near shore.

Overexposure To Sunlight

When sea temperatures are high, intense solar radiation can worsen bleaching, especially in shallow-water corals.

Extreme Low Tides

During unusually low tides, corals may be exposed to air and direct sunlight.

This causes physiological stress and bleaching.

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FAQs On Movement Of Ocean Water