Movements of Ocean Water

1.Horizontal and Vertical Motions

• Horizontal and Vertical Motions of Ocean WaterImportance 3/5
  Which properties of ocean water, and which outside forces, set it in motion? Understand how the movements of ocean water are sorted into horizontal and vertical ones. Do tides also create any horizontal movement?
• Movement of Water in Currents and in WavesImportance 2/5
  Does the water itself travel from place to place in an ocean current? Does it do so in a wave? Be clear about the difference between the two.

2.Waves

• Energy and Water Movement in a WaveImportance 4/5
  As a wave passes, what actually moves across the ocean surface, and how do the water particles move? Understand the roles of wind and gravity in making a wave advance. Does surface wave motion disturb the deep water below?
• Wind, Wave Growth and Maximum Wave HeightImportance 3/5
  How does a wave grow from a small ripple to a white cap as the wind strengthens? Understand the three factors that set the maximum height of a wave, including the term "fetch". Where are the largest waves found, and how far can waves travel before they break as surf?
• Wave Size and ShapeImportance 2/5
  What does the size and shape of a wave tell you about where it was formed? Distinguish steep waves from slow, steady ones in terms of their age and distance from the source.
• Waves Approaching the Shore and BreakingImportance 3/5
  Why does a wave slow down as it nears the beach? Is the depth at which a wave starts to slow the same as the condition for it to break? Understand how wave height and water depth relate to breaking, and what happens to the wave's energy on the shore.
• Wave Crest, Trough, Wave Height and AmplitudeImportance 3/5
  Remember what crest and trough mean and how wave height is measured. How is wave amplitude related to wave height? Be careful not to treat the two as the same.
• Wave Period, Wavelength, Wave Speed and Wave FrequencyImportance 3/5
  Know the meaning of each of these four terms. Which are measured in time and which in distance? Remember the unit used for wave speed and the time interval used for wave frequency.
• Causes of TsunamisImportance 4/5
  What is a tsunami, and what is its technical name? Why is it wrong to call it a "tidal wave"? Where does its energy come from, given that wind is not the source? Know which cause is the most common, and the other possible causes such as volcanic eruptions and landslides.
• Characteristics of Tsunamis in Deep Water and Near the CoastImportance 4/5
  Understand how a tsunami's wavelength, speed and height behave in the open ocean, and why it is hard to notice there. What happens to its speed and height as it enters shallow water? Does a tsunami usually come as a single wave or as a series of waves? Know the warning signs too.

3.Tides

• Tides and SurgesImportance 3/5
  What is a tide, and what mainly causes it? How does a surge differ from a tide in its cause and in how regularly it occurs?
• Causes of TidesImportance 5/5UPSC 2015
  Which three forces are behind tides? Remember the relative roles of the Moon and the Sun, and understand why one of them dominates even though the other is far more massive. What role does centrifugal force play against gravity?
• Tide-Generating Force and the Two Tidal BulgesImportance 4/5
  What is the tide-generating force? Explain why a bulge forms on the side of the Earth facing the Moon and also on the opposite side. Which matter more in forming bulges, horizontal or vertical forces?
• Interval Between Successive High TidesImportance 3/5
  Why are two high tides at a place not exactly twelve hours apart? Remember the usual interval and the time a tidal centre takes to come back under the Moon. Understand how the Moon's own movement causes the daily delay.
• Continental Shelves, Islands, Bays and Tidal CurrentsImportance 3/5UPSC 2004
  How do wide continental shelves and mid-ocean islands change the height of tidal bulges? Understand why funnel-shaped bays and estuaries magnify tides. What are tidal currents?
• Tides of the Bay of FundyImportance 4/5
  Where are the highest tides in the world found, and roughly how high is the tidal range? Understand the role of the bay's shape in making the range so great. With only about six hours of rising water, how fast must the water rise to cover a range of that size?
• Tidal BoresImportance 3/5UPSC 2004
  What is a tidal bore, and in what kind of estuary or river does it form? On which phase of the tide does it form, and how does it differ between spring tides and neap tides? Remember the Indian river and the river in the world where it is most prominent.
• Semi-Diurnal, Diurnal and Mixed TidesImportance 4/5
  Distinguish these three types by the number and height of their high and low tides in a day. Which type is the most common? Remember where mixed tides occur, and where diurnal tides are found.
• Spring Tides and Neap TidesImportance 5/5UPSC 2001
  How are the Sun, Moon and Earth placed in spring tides and in neap tides? Know the terms syzygy and quadrature. When in the lunar month does each occur, and how many times? Understand how each affects the height of high and low tides.
• Perigee and Apogee and Their Effect on Tidal RangeImportance 4/5
  Be clear about what perigee and apogee mean and how often each occurs. Understand how each changes the tidal range. Do not confuse them with perihelion and aphelion, which describe a different pair of bodies.
• Perihelion and Aphelion and Their Effect on Tidal RangeImportance 4/5
  Around which dates is the Earth nearest to the Sun and farthest from it? Understand how the tidal range differs at these two times, and how large this effect is compared with the effect of spring and neap tides.
• Ebb and Flow (Flood)Importance 3/5
  Which term describes the falling tide, and which describes the rising tide? Remember what each term means.
• Tides in Navigation, Fishing, Harbours and EstuariesImportance 4/5UPSC 2000, 2004
  Why can tides be predicted well in advance, and how does this help navigators and fishermen? Understand why tidal height matters for harbours with shallow bars near rivers and estuaries. How do tides help clean estuaries?
• Tidal PowerImportance 3/5
  Which countries run tidal power plants today, and which plant is the largest in the world? What happened to the Durgaduani project in the Sunderbans? Which Indian coasts have the most tidal potential, and why does India still have no commercial tidal plant?

4.Ocean Currents

• Primary and Secondary Forces of Ocean CurrentsImportance 5/5UPSC 2002, 2012
  How do primary forces differ from secondary forces? Understand how each primary force acts on ocean water: solar heating (and the slope it creates), wind, gravity and the Coriolis force. In which direction does the Coriolis force deflect water in each hemisphere, and does it start a current or only deflect one?
• Ekman Transport and the Ekman SpiralImportance 3/5
  At about what angle to the wind does surface water move, and to which side in each hemisphere? What is the Ekman spiral, and what is net Ekman transport? Understand how it causes coastal upwelling and how it helps in forming gyres.
• Density Differences and Vertical Movement of Ocean WaterImportance 4/5
  How do salinity and temperature change the density of water? Understand why denser water sinks and lighter water rises. How does this drive the movement of cold polar water towards the equator and warm surface water towards the poles?
• Drift and Speed of Ocean CurrentsImportance 2/5
  What do "drift" and "strength" of a current mean, and in what unit is drift measured? What does "drift" mean in current names such as North Atlantic Drift? How does current speed change with depth? Remember the usual speeds near the surface and in deep water.
• Surface Currents and Deep Water CurrentsImportance 4/5
  Remember what share of ocean water each type makes up and how deep the surface layer goes. What moves deep water, and where does it sink?
• Thermohaline Circulation (Global Conveyor Belt)Importance 4/5
  What drives thermohaline circulation? Understand where water sinks and where it rises, and how the circulation spreads heat and nutrients around the oceans.
• Cold and Warm Currents and Their Location Along Continental CoastsImportance 5/5
  What makes a current warm or cold? On which coasts of the continents is each found in low and middle latitudes? Remember how the pattern differs at high latitudes in the Northern Hemisphere.
• Western and Eastern Boundary CurrentsImportance 3/5UPSC 2021
  Distinguish these two kinds of current by speed and width. Are all western boundary currents warm? Understand why the western edges of ocean basins have the stronger currents. What part does the change in the Coriolis effect with latitude play? How are eastern boundary currents linked to coastal upwelling and productivity?
• Influence of Prevailing Winds, Coriolis Force and Monsoons on Ocean CirculationImportance 4/5
  How does ocean circulation follow the air circulation over the oceans at middle and higher latitudes? Understand how monsoon winds affect currents. In which direction does the Coriolis force turn warm currents moving out of low latitudes in each hemisphere?
• Heat Transport by Ocean CirculationImportance 3/5UPSC 2002
  How do currents move heat from one latitude belt to another? Understand the direction in which cold polar water and warm tropical water travel.
• Gyres and the Sargasso SeaImportance 4/5
  What is a gyre, and how does one form? In which direction does a subtropical gyre turn in each hemisphere, and which way does the Indian Ocean gyre turn? Do subpolar gyres turn the same way? Know the five main gyres and the currents that make them up. Where is the Sargasso Sea, why is it unusual, and where does its name come from?
• Major Currents of the Atlantic OceanImportance 5/5UPSC 2015, 2024
  Know the main currents of the North Atlantic (North Equatorial, Gulf Stream, North Atlantic Drift, Canary, Labrador, East Greenland), the South Atlantic (South Equatorial, Brazil, Benguela, Falkland) and the equatorial counter current. Which are warm and which cold? Where does each flow?
• Major Currents of the Pacific OceanImportance 4/5
  Know the main currents of the North Pacific (North Equatorial, Kuroshio, North Pacific, California, Oyashio, Alaska) and the South Pacific (South Equatorial, East Australian, Peru or Humboldt). Which are warm and which cold? Also learn the Antarctic Circumpolar Current, also known as the West Wind Drift, which encircles Antarctica across all the oceans.
• Major Currents of the Indian Ocean and Their Seasonal ReversalImportance 4/5UPSC 1997
  Remember the main currents of the southern Indian Ocean (South Equatorial, Agulhas, Mozambique, West Australian) and whether each is warm or cold. In the north, know the Somali Current and the monsoon currents. How does their direction change between the two monsoons?
• Effect of Ocean Currents on Coastal ClimateImportance 5/5
  Explain the climate of three kinds of coast: tropical west coasts, middle and high latitude west coasts, and tropical east coasts. How does the nearby current shape temperature, range, fog, rainfall and aridity? Use north-west Europe as an example.
• Mixing Zones of Warm and Cold Currents and Fishing GroundsImportance 4/5UPSC 2013
  Why does the meeting of warm and cold currents favour fish? Understand the role of oxygen and plankton. Which are the well-known fishing grounds of the world, and are all of them found in such mixing zones?
• Water Masses and Their Impact on Marine LifeImportance 3/5
  Be clear about what a water mass is and how it differs from an ocean current. Understand how water masses decide which marine ecosystems can grow, such as coral reefs, kelp forests and deep-sea life, and how they affect productivity.
• Atlantic Meridional Overturning Circulation (AMOC)Importance 4/5
  How does the AMOC work: what flows north at the surface, where does it sink and how does it return? Why is melting ice a danger to it? Understand how a weaker AMOC could affect Western Europe, storms, sea level and fisheries.
• Marine HeatwavesImportance 3/5
  What is a marine heatwave? Understand its causes (warming, high pressure, changes in currents, El Nino, feedback loops) and its effects, especially on corals. How has the frequency of marine heatwaves changed since the early 1980s?
• Impact of Climate Change on Ocean CurrentsImportance 2/5
  How could warming change the temperature and salinity differences that drive thermohaline circulation? Understand the effects on upwelling, oxygen, marine species and coastal communities.

1. 1.

   With reference to ocean waves, consider the following statements:
   1. Water particles travel long distances along with the wave as it moves across the ocean.
   2. The largest waves are found close to the shore.
   Which of the statements given above is/are correct?

   1. A1 only
   2. B2 only
   3. CBoth 1 and 2
   4. DNeither 1 nor 2
2. 2.

   Consider the following statements:
   Statement-I: A wave slows down as it approaches the beach.
   Statement-II: Friction occurs between the moving water and the sea floor.
   Which one of the following is correct in respect of the above statements?

   1. ABoth Statement-I and Statement-II are correct and Statement-II explains Statement-I
   2. BBoth Statement-I and Statement-II are correct and Statement-II does not explain Statement-I
   3. CStatement-I is correct but Statement-II is incorrect
   4. DStatement-I is incorrect but Statement-II is correct
3. 3.

   Consider the following statements:
   1. Steep waves are old waves that have travelled from far-away places.
   2. The maximum height of a wave is determined mainly by tidal forces.
   Which of the statements given above is/are correct?

   1. A1 only
   2. B2 only
   3. CBoth 1 and 2
   4. DNeither 1 nor 2
4. 4.

   A wave approaching the shore breaks when the depth of water becomes less than

   1. ATwice the wavelength of the wave
   2. BThe height of the wave
   3. CHalf the wavelength of the wave
   4. DThe amplitude of the wave
5. 5.

   Consider the following statements about the characteristics of waves:
   1. Wave height is the vertical distance from the bottom of a trough to the top of a crest.
   2. Wave period is the time interval between two successive crests or troughs passing a fixed point.
   3. Wavelength is the horizontal distance between two successive crests.
   4. Wave speed is measured in metres per second.
   How many of the above statements are correct?

   1. AOnly one
   2. BOnly two
   3. COnly three
   4. DAll four
6. 6.

   With reference to tides, consider the following statements:
   1. On the earth's surface, vertical tide-generating forces are more important than horizontal ones in generating tidal bulges.
   2. The tide-generating force is the difference between the moon's gravitational attraction and the centrifugal force.
   Which of the statements given above is/are correct?

   1. A1 only
   2. B2 only
   3. CBoth 1 and 2
   4. DNeither 1 nor 2
7. 7.

   Consider the following pairs:

   Type of tide	Feature
   1. Semi-diurnal	The most common pattern: two high and two low tides each day
   2. Diurnal	Only one high tide and one low tide each day
   3. Mixed	Successive tides of approximately the same height

   How many of the pairs given above are correctly matched?

   1. AOnly one
   2. BOnly two
   3. CAll three
   4. DNone
8. 8.

   With reference to spring and neap tides, consider the following statements:
   1. Spring tides occur when the sun, the moon and the earth are in a straight line, twice a month.
   2. Neap tides occur when the sun and the moon are at right angles to each other.
   3. The sun's attraction is more than twice as strong as the moon's.
   Which of the statements given above is/are correct?

   1. A1 only
   2. B1 and 2 only
   3. C2 and 3 only
   4. D1, 2 and 3
9. 9.

   Consider the following statements:
   1. When the moon is closest to the earth (perigee), the tidal range is greater than normal.
   2. When the earth is farthest from the sun (aphelion), around 4th July, tidal ranges are much greater than average.
   Which of the statements given above is/are correct?

   1. A1 only
   2. B2 only
   3. CBoth 1 and 2
   4. DNeither 1 nor 2
10. 10.

    With reference to the primary forces that initiate ocean currents, consider the following statements:
    1. Because of heating, ocean water near the equator is about 8 cm lower in level than in the middle latitudes.
    2. The Coriolis force causes water to move to the left in the northern hemisphere.
    Which of the statements given above is/are correct?

    1. A1 only
    2. B2 only
    3. CBoth 1 and 2
    4. DNeither 1 nor 2
11. 11.

    With reference to the speed of ocean currents, consider the following statements:
    1. Currents are usually strongest near the surface and may attain speeds of over five knots.
    2. At depths, currents are generally slow, with speeds of less than 0.5 knots.
    Which of the statements given above is/are correct?

    1. A1 only
    2. B2 only
    3. CBoth 1 and 2
    4. DNeither 1 nor 2
12. 12.

    Consider the following pairs:

    Ocean current type	Feature
    1. Surface currents	About 10 per cent of ocean water, in the upper 400 m
    2. Deep water currents	About 90 per cent of ocean water, moving due to variations in density and gravity
    3. Sinking of deep waters	Occurs mainly at low latitudes

    How many of the pairs given above are correctly matched?

    1. AOnly one
    2. BOnly two
    3. CAll three
    4. DNone
13. 13.

    With reference to cold and warm ocean currents, consider the following statements:
    1. Cold currents are usually found on the west coasts of continents in the low and middle latitudes.
    2. Warm currents are usually observed on the east coasts of continents in the low and middle latitudes.
    Which of the statements given above is/are correct?

    1. A1 only
    2. B2 only
    3. CBoth 1 and 2
    4. DNeither 1 nor 2
14. 14.

    Consider the following statements:
    Statement-I: The best fishing grounds of the world exist mainly in zones where warm and cold currents mix.
    Statement-II: The mixing of warm and cold currents helps replenish oxygen and favours the growth of plankton, the primary food for fish.
    Which one of the following is correct in respect of the above statements?

    1. ABoth Statement-I and Statement-II are correct and Statement-II explains Statement-I
    2. BBoth Statement-I and Statement-II are correct and Statement-II does not explain Statement-I
    3. CStatement-I is correct but Statement-II is incorrect
    4. DStatement-I is incorrect but Statement-II is correct
15. 15.

    Consider the following statements:
    1. West coasts of continents in the middle and higher latitudes are bordered by warm waters, giving a marine climate with cool summers and relatively mild winters.
    2. Anticyclonic oceanic circulation in the middle latitudes is more pronounced in the northern hemisphere than in the southern hemisphere.
    Which of the statements given above is/are correct?

    1. A1 only
    2. B2 only
    3. CBoth 1 and 2
    4. DNeither 1 nor 2

1. 1.

   UPSC 2015

   What explains the eastward flow of the equatorial counter-current?

   1. AThe Earth's rotation on its axis
   2. BConvergence of the two equatorial currents
   3. CDifference in salinity of water
   4. DOccurrence of the belt of calm near the equator
2. 2.

   UPSC 2015

   Tides occur in the oceans and seas due to which among the following?
   1. Gravitational force of the Sun
   2. Gravitational force of the Moon
   3. Centrifugal force of the Earth
   Select the correct answer using the code given below.

   1. A1 only
   2. B2 and 3 only
   3. C1 and 3 only
   4. D1, 2 and 3
3. 3.

   UPSC 2013

   The most important fishing grounds of the world are found in the regions where

   1. Awarm and cold atmospheric currents meet
   2. Brivers drain out large amounts of freshwater into the sea
   3. Cwarm and cold oceanic currents meet
   4. Dcontinental shelf is undulating
4. 4.

   UPSC 2012

   Consider the following factors :
   1. Rotation of the Earth
   2. Air pressure and wind
   3. Density of ocean water
   4. Revolution of the Earth
   Which of the above factors influence the ocean currents?

   1. A1 and 2 only
   2. B1, 2 and 3
   3. C1 and 4
   4. D2, 3 and 4
5. 5.

   UPSC 2004

   Which one of the following statements is not correct?

   1. AGulfs with narrow fronts and wider rears experience high tides
   2. BTidal currents take place when a gulf is connected with the open sea by a narrow channel
   3. CTidal bore occurs when a tide enters the narrow and shallow estuary of a river
   4. DThe tidal nature of the mouth of the river Hooghly is of crucial importance to Kolkata as port
6. 6.

   UPSC 2002

   Consider the following statements:
   1. Ocean currents are the slow surface movement of water in the ocean.
   2. Ocean currents assist in maintaining the Earth’s heat balance.
   3. Ocean currents are set in motion primarily by prevailing winds.
   4. Ocean currents are affected by the configuration of the ocean floor.
   Which of these statements are correct?

   1. A1 and 2
   2. B2, 3 and 4
   3. C1, 3 and 4
   4. D1, 2, 3 and 4
7. 7.

   UPSC 2001

   Assertion (A): During the Neap Tides, the high tide is lower and the low tide is higher than usual. Reason (R): The Neap Tide, unlike the Spring Tide, occurs on the New Moon instead of on the Full Moon.

   1. ABoth A and R are individually true, and R is the correct explanation of A
   2. BBoth A and R are individually true, but R is NOT a correct explanation of A
   3. CA is true, but R is false
   4. DA is false, but R is true
8. 8.

   UPSC 2000

   Consider the following statements:
   I. Tides are of great help in navigation and fishing.
   II. High tide enables big ships to enter or leave the harbour safely.
   III. Tide prevents siltation in the harbours.
   IV. Kandla and Diamond Harbour are tidal ports.
   Which of these statements are correct?

   1. AI and IV
   2. BII, III and IV
   3. CI, II and III
   4. DI, II, III and IV
9. 9.

   UPSC 1997

   Which one of the following factors is responsible for the change in the regular direction of the ocean currents in the Indian Ocean?

   1. AIndian Ocean is ‘half an ocean’
   2. BIndian Ocean has monsoon drift
   3. CIndian Ocean is a land-locked ocean
   4. DIndian Ocean has greater variation in salinity
10. 10.

    UPSC 2024

    Which of the following is/are correct inference/inferences from isothermal maps in the month of January ?
    1. The isotherms deviate to the north over the ocean and to the south over the continent.
    2. The presence of cold ocean currents, Gulf Stream and North Atlantic Drift make the North Atlantic Ocean colder and the isotherms bend towards the north.
    Select the answer using the code given below :

    1. A1 only
    2. B2 only
    3. CBoth 1 and 2
    4. DNeither 1 nor 2
11. 11.

    UPSC 2021

    Consider the following statements :
    1. In the tropical zone, the western sections of the oceans are warmer than the eastern sections owing to the influence of trade winds.
    2. In the temperate zone, westerlies make the eastern sections of oceans warmer than the western sections.
    Which of the statements given above is/are correct?

    1. A1 only
    2. B2 only
    3. CBoth 1 and 2
    4. DNeither 1 nor 2