NCERT
Every NCERT book that matters for UPSC — open a book, then a chapter. Learn each chapter's concepts, then how UPSC tests them — with diagrams, flowcharts and the past questions to attempt.
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← Fundamentals of Physical Geography — all chaptersMovements of Ocean Water
Start here: why this chapter matters
In simple wordsThe sea never sits still. The wind ruffles it into waves; the moon lifts and lowers it twice a day as tides; and vast rivers within the ocean — currents — carry warm and cold water across the globe. This chapter explains all three.
Ocean water is moved by its own properties — temperature, salinity, density — and by outside forces — the sun, the moon and the winds. Horizontal motions are waves and currents; vertical motions are tides, and the upwelling of cold water and sinking of surface water. In a current, the water itself travels; in a wave, the water stays roughly in place while the wave train moves on.
- Builds on Chapter 9: the same winds, pressure belts and Coriolis force drive the currents.
- Builds on Chapter 12: temperature, salinity and density differences drive deep currents.
- Links back to Chapters 8, 10 and 11: currents bend isotherms, cause coastal fog and deserts, and shape climates.
- UPSC: GS1 (ocean currents, tides, fisheries) and GS3 (tidal energy, coastal disasters, blue economy).
| Word | What it means here |
|---|---|
| Wave | Energy moving across the water surface |
| Crest / trough | The highest / lowest point of a wave |
| Tide | The regular rise and fall of sea level, once or twice a day |
| Surge | A rise in sea level caused by wind and air pressure — irregular, unlike tides |
| Ocean current | A steady flow of a large body of water in a definite direction, like a river in the sea |
| Gyre | A huge circular system of currents round an ocean basin |
| Upwelling | Cold, nutrient-rich water rising from below to the surface |
| Knot | One nautical mile per hour — the unit for wave and current speed |
At a glance — the six ideas to carry away
- Waves move energy, not water — particles travel in circles; wind supplies the energy.
- Tides: the moon's gravity (mainly), the sun's, and centrifugal force → two tidal bulges.
- Spring tides at new and full moon (in line); neap tides at the quarters (right angles), ~7 days later.
- Highest tides: Bay of Fundy, Canada (15–16 m).
- Currents are driven by solar heating, wind, gravity, Coriolis; density differences drive deep flow.
- Warm currents on east coasts, cold on west coasts (low and middle latitudes); fishing grounds where they meet.
1. Waves
In simple wordsIn a stadium, a ‘Mexican wave’ travels right round the ground, but nobody leaves their seat — each person just stands up and sits down. Ocean waves are the same: the energy races across the sea, while each bit of water only goes round in a small circle and ends up roughly where it started.
Waves are energy, not water, moving across the surface. Wind provides the energy, and it is released on the shoreline. Surface motion seldom disturbs the still, deep bottom water. Most waves are made by wind pushing against water: a breeze of 2 knots or less on calm water raises ripples, which grow as the wind strengthens until white caps appear. Waves can travel thousands of km before breaking as surf. The largest waves are in the open ocean, and they keep growing as they absorb wind energy.
Wind pushes the water forward while gravity pulls the crests down; the falling water pushes the former troughs up, and the wave moves on. Beneath the wave the water moves in circles — carried up and forward as the wave arrives, down and back as it passes.
Reading NCERT Figure 13.1 — Motion of waves and water molecules (page 108)
- A wave travels to the right. Labels show ‘crest falling’ above each crest and ‘trough rising’ below each trough — gravity pulls crests down while the water beneath pushes troughs up, and that hand-over is what moves the wave forward.
- Small curved arrows inside the water trace circular paths: water rises and moves forward under an approaching crest, then sinks and moves back as it passes.
| Term (NCERT box) | Meaning |
|---|---|
| Crest / trough | Highest / lowest point of a wave |
| Wave height | Vertical distance from the bottom of a trough to the top of a crest |
| Wave amplitude | Half the wave height |
| Wave period | Time between two successive crests (or troughs) passing a fixed point |
| Wavelength | Horizontal distance between two successive crests |
| Wave speed | Rate at which the wave moves through water, in knots |
| Wave frequency | Number of waves passing a point in one second |
Near the shore a wave slows down because of friction with the sea floor; when the water depth is less than half the wavelength, NCERT says, the wave breaks. A wave's shape tells its story: steep waves are young and probably raised by local wind; slow, steady waves (swell) come from far away, possibly from another hemisphere. Maximum wave height depends on the strength of the wind, how long it blows and the area over which it blows in one direction.
Beyond NCERT — a precise wordOceanographers say a wave starts to ‘feel the bottom’ — slowing and steepening — once the depth is less than about half its wavelength; it actually breaks later, in water roughly as deep as the wave is high. The distance over which wind blows is called the fetch. Tsunamis are not wind waves: they are set off by undersea earthquakes (Chapter 3).
2. Tides and why they happen
In simple wordsSwing a bucket of water round your head: the water presses outward, away from your hand. The earth and moon swing round each other in the same way. On the side facing the moon, the moon's pull wins and drags the ocean towards it; on the far side, the ‘swing’ (centrifugal force) wins and the ocean bulges outward. Two bulges — and the earth turns through both each day.
A tide is the periodic rise and fall of sea level, once or twice a day, caused mainly by the attraction of the sun and the moon. Movements caused by weather — winds and pressure changes — are surges, which are not regular. The moon's gravity is the main cause, the sun's a lesser one; centrifugal force, which counterbalances gravity, is the other part.
Reading NCERT Figure 13.2 — Relation between gravitational forces and tides (page 109)
- Three rows, each with the Earth on the left, the Moon and then the Sun lined up on the right.
- Gravitational force: arrows on the Earth all point towards the Moon; a bulge forms on the Moon's side.
- Centrifugal force: arrows point away from the Moon; a bulge forms on the far side.
- Two resultant tidal bulges: the Earth is drawn inside an elongated outline stretched towards and away from the Moon.
- Because the Sun is drawn in line with the Moon, the figure also shows the set-up for a spring tide.
⤵ How two tidal bulges form
Moon's gravitystronger on the side facing the Moon, weaker on the far side
Centrifugal forcethe same everywhere, pointing away from the Moon
Near sidegravity > centrifugal → bulge towards the Moon
Far sidecentrifugal > gravity → bulge away from the Moon
Tide-generating force = the differenceits horizontal part matters most
The earth rotates through both bulgestwo high tides and two low tides
Tidal bulges are higher on wide continental shelves and lower at mid-ocean islands. Funnel-shaped bays and estuaries greatly magnify tides. When tides are channelled between islands or into bays and estuaries, they become tidal currents.
Reading the box on page 110 — Tides of the Bay of Fundy
- The Bay of Fundy (Nova Scotia, Canada) has the world's highest tides: a tidal bulge of 15–16 m.
- With two highs and two lows a day, each rise takes about 6 hours; NCERT estimates about 240 cm an hour (1,440 cm ÷ 6 h) — fast enough to trap a walker below the cliffs.
- Slip: 1,440 cm is 14.4 m, a little less than the 15–16 m given. The idea, not the arithmetic, is what matters.
Beyond NCERT (asked by UPSC)
- Because the moon moves along its orbit, the earth needs about 24 hours 50 minutes to face it again — so high tides come about 12 hours 25 minutes apart and roughly 50 minutes later each day.
- High tides at the antipodes (far side) come from centrifugal force together with gravity (UPSC 1986); tides are caused by the gravity of both the sun and the moon and by centrifugal force (UPSC 2015).
- A tidal bore is a wall of water that rushes up a narrow, shallow estuary on the incoming tide — e.g. the Hooghly (UPSC 2004).
3. Types of tides
In simple wordsTides are like a heartbeat with a rhythm that differs from place to place — two beats a day in most places, one in some, uneven in others — and with a monthly rhythm too: stronger tides when sun and moon pull together, weaker ones when they pull across each other.
| By frequency | Pattern | Where (NCERT) |
|---|---|---|
| Semi-diurnal | Two high and two low tides a day, successive ones of about the same height | The most common pattern |
| Diurnal | One high and one low tide a day | — |
| Mixed | Tides varying in height | West coast of North America and many Pacific islands |
By sun–moon–earth position. Spring tides: when the sun, moon and earth are in a straight line, the tide is higher — twice a month, at full moon and new moon. Neap tides: about seven days later, when sun and moon are at right angles, their forces counteract; the moon's pull, though more than twice the sun's, is reduced.
| Situation | Effect on tides (NCERT) |
|---|---|
| Perigee (moon closest to earth, once a month) | Unusually high and low tides — tidal range greater than normal |
| Apogee (moon farthest, two weeks later) | Tidal ranges less than average |
| Perihelion (earth closest to sun, ~3 January) | Tidal ranges greater, with unusually high and low tides |
| Aphelion (earth farthest, ~4 July) | Tidal ranges less than average |
| Ebb | The falling tide, from high to low water |
| Flow / flood | The rising tide, from low to high water |
Exam traps
- Neap tides occur at the first and third quarters, when sun and moon are at right angles (UPSC 1991) — not at new moon (UPSC 2001: during neaps the high tide is lower and the low tide higher than usual — true; ‘neaps occur at new moon’ — false).
- Spring tides happen at both new and full moon (UPSC 1988).
- ‘Spring’ has nothing to do with the season.
- Perigee is about the moon; perihelion is about the sun (NCERT Q1-iii and iv: perigee; January).
Beyond NCERT — how big is the perihelion effect?NCERT says tidal ranges are ‘much greater’ at perihelion. The effect is real but small: the earth is only about 3% closer to the sun in January, which strengthens the sun's share of the tide by roughly a tenth — a few per cent of the total. The moon's perigee has a bigger effect.
4. Why tides matter
In simple wordsTides are perfectly predictable, like a train timetable — which makes them useful. Sailors wait for high tide to cross a shallow harbour mouth; the outgoing tide flushes mud and dirt out of river mouths; and the rush of water can spin turbines.
- Prediction: earth–moon–sun positions are known accurately, so tides can be forecast well ahead — useful for navigators and fishermen.
- Navigation: tidal heights matter at harbours near rivers and in estuaries with shallow ‘bars’ at the entrance that block ships at low water.
- Cleaning: tides help desilt sediments and remove polluted water from estuaries.
- Power: tidal energy is used in Canada, France, Russia and China; NCERT mentions a 3 MW project at Durgaduani in the Sunderbans, West Bengal.
Beyond NCERT (asked by UPSC)Kandla (Gulf of Kachchh) and Diamond Harbour (on the Hooghly) are tidal ports, and tides help navigation, fishing and the clearing of silt (UPSC 2000 — all four statements correct). India's best tidal-energy sites are the Gulfs of Kachchh and Khambhat in Gujarat and the Sunderbans, where funnel-shaped inlets amplify the tidal range.
5. Ocean currents: causes and types
In simple wordsBlow across a cup of tea and the surface starts to swirl. The trade winds and westerlies do this to whole oceans. Add the spin of the earth (which bends the flow), the slight downhill slope from the warm, swollen tropics, and the sinking of cold, salty water near the poles — and you get great rivers flowing through the sea.
| Force | How it moves water (NCERT) |
|---|---|
| Heating by the sun (primary) | Warm water expands, so near the equator the sea is about 8 cm higher than in the middle latitudes; water flows down this slight slope |
| Wind (primary) | Pushes the surface water; friction between wind and water moves it along |
| Gravity (primary) | Pulls water down the ‘pile’ and creates gradients |
| Coriolis force (primary) | Turns the flow to the right in the NH and the left in the SH; the large accumulations of water and the flow round them are gyres — big circular currents in every ocean basin |
| Density differences | Saltier and colder water is denser and sinks; lighter water rises. Cold water sinks at the poles and creeps towards the equator; warm surface water flows poleward to replace it |
NCERT slipThe text promises ‘primary forces that initiate the movement’ and ‘secondary forces that influence the currents to flow’ but lists only the four primary ones. Secondary influences named elsewhere in the chapter: density differences (salinity, temperature), the shape of the coastline and ocean basin, and monsoon winds.
| Classification | Types (NCERT) |
|---|---|
| By depth | Surface currents: about 10% of ocean water, the upper 400 m · Deep-water currents: the other 90%, moved by density and gravity; deep water sinks at high latitudes where it is cold enough to become dense |
| By temperature | Cold currents bring cold water into warm areas — usually on west coasts in low and middle latitudes (both hemispheres) and on east coasts in high northern latitudes · Warm currents bring warm water into cold areas — usually on east coasts in low and middle latitudes (both hemispheres) and on west coasts in high northern latitudes |
Reading the box on page 111 — Characteristics of ocean currents
- A current's speed is its drift, measured in knots; a fast current is strong.
- Currents are strongest at the surface — sometimes over 5 knots — and slow with depth to under 0.5 knots. Most currents flow at 5 knots or less.
⤵ What sets a current in motion (NCERT exercise Q3-ii)
Sun heats the tropicswater expands — sea ~8 cm higher at the equator
Winds push the surfacetrade winds westward, westerlies eastward
Gravity pulls water down the slopeCoriolis turns it right (NH) / left (SH)
Gyres form round each ocean basinclockwise in the NH, anticlockwise in the SH
Density differences add deep flowcold, salty water sinks at the poles and spreads
Beyond NCERT (asked by UPSC)
- The earth's rotation, air pressure and wind and density influence currents; the earth's revolution does not (UPSC 2012).
- UPSC 2002 accepted all four: currents are slow surface movements, help keep the earth's heat balance, are set in motion mainly by prevailing winds, and are shaped by the configuration of the ocean.
- The equatorial counter-current flows east between the two westward equatorial currents because water piled up in the west by the trades flows back through the calm doldrums (UPSC 2015 key: ‘convergence of the two equatorial currents’).
- The deep, density-driven circulation is often called the thermohaline circulation or ‘global conveyor belt’.
6. The major ocean currents
In simple wordsEach ocean has one or two big wheels of current. Learn one wheel and you can work out the rest: westward along the equator, poleward and warm on the western side of the ocean, eastward with the westerlies, then back towards the equator, cold, on the eastern side.
Major currents follow the prevailing winds and the Coriolis force, so ocean circulation roughly matches the atmosphere's. Over the oceans in the middle latitudes the air circulation is mainly anticyclonic (more so in the SH), and so are the currents; at higher latitudes, where winds are cyclonic, the currents follow suit. Where the monsoon is strong, monsoon winds steer the currents. Ocean circulation carries heat from one latitude belt to another, like the atmosphere: cold polar water moves towards the tropics, warm low-latitude water moves poleward.
Reading NCERT Figure 13.3 — Major currents in the Pacific, Atlantic and Indian Oceans (page 112)
- The legend uses dashed arrows for cold currents and solid arrows for warm ones; the schematic above follows the same convention.
- Named currents — Atlantic: N. Equatorial, Gulf Stream, North Atlantic Drift, Canaries (cold), Labrador (cold), Eq. Counter, S. Equatorial, Brazilian, Falkland (cold), Benguela (cold). Pacific: N. Equatorial, Kuroshio, N. Pacific Drift, California (cold), Alaska, Oyashio (cold), Eq. Counter, S. Equatorial, Humboldt/Peru (cold). Indian: S. Equatorial, Agulhas, West Australian (cold), Eq. Counter. Southern: West Wind Drift (cold) all round Antarctica.
- The northern Indian Ocean has arrows but no names — its currents reverse with the monsoon.
- Some currents are not on the map (e.g. the East Australian, marked * above, Beyond NCERT).
| Ocean | Warm currents | Cold currents |
|---|---|---|
| North Atlantic | North Equatorial, Gulf Stream, North Atlantic Drift | Canaries, Labrador |
| South Atlantic | South Equatorial, Brazilian | Benguela, Falkland, West Wind Drift |
| North Pacific | North Equatorial, Kuroshio, North Pacific Drift, Alaska | California, Oyashio |
| South Pacific | South Equatorial (East Australian — Beyond NCERT) | Humboldt (Peru), West Wind Drift |
| Indian | South Equatorial, Agulhas | West Australian, West Wind Drift |
| All three | Equatorial counter-currents flowing east | — |
Beyond NCERT (asked by UPSC)
- In the northern Indian Ocean the monsoon drift reverses with the seasons: it flows clockwise in summer (south-west monsoon) and anticlockwise in winter (north-east monsoon). This is why currents there change direction (UPSC 1997).
- Match by coast: south-eastern USA — Florida current; west coast of southern Africa — Benguela; south-west South America — Peruvian; south-east Japan — Kuroshio (UPSC 1985). The Labrador is cold; the Gulf Stream and Kuroshio are warm (UPSC 1989).
7. Effects of ocean currents
In simple wordsA warm current is like a radiator running along a coast; a cold current is like an air-conditioner. They change the temperature, rainfall and even the fish of the places they pass.
| Where | Current | Effect on climate (NCERT) |
|---|---|---|
| West coasts, tropical and subtropical latitudes (not right at the equator) | Cool waters | Relatively low temperatures, narrow daily and annual ranges; fog, but generally arid (e.g. Atacama, Namib — Beyond NCERT) |
| West coasts, middle and high latitudes | Warm waters | Distinct marine climate: cool summers, relatively mild winters, narrow annual range (e.g. north-west Europe) |
| East coasts, tropical and subtropical latitudes | Warm currents | Warm and rainy climates — on the western margins of the subtropical anticyclones |
| Where warm and cold currents mix | Both | Oxygen replenished; plankton grows — food for fish; the world's best fishing grounds |
⤵ Why fish gather where currents meet
Warm and cold currents mixe.g. Gulf Stream + Labrador; Kuroshio + Oyashio
Oxygen and nutrients are replenishedcold water is rich in nutrients and dissolved oxygen
Plankton multiplythe primary food of fish
Fish populations boomthe world's best fishing grounds
North-west Europe (NCERT exercise Q3-i)The warm North Atlantic Drift, the continuation of the Gulf Stream, carries tropical heat north-east. The westerlies blow that warmth onto Europe's west coast, so ports such as those of Norway stay ice-free in winter and winters are far milder than at the same latitude in Canada or Siberia; the Chapter 8 January isotherms bend sharply north over the North Atlantic for this reason.
Beyond NCERT (asked by UPSC)
- The most important fishing grounds lie where warm and cold ocean currents meet — the Grand Banks off Newfoundland, the Dogger Bank in the North Sea, and the waters off Japan (UPSC 2013).
- Upwelling zones (off Peru, California, Namibia) are rich because they bring nutrients to the surface (UPSC 2011 — not decomposers or bottom-dwellers).
- In the tropics the trade winds pile warm water on the western side of the oceans, so it is warmer than the eastern side; in the temperate zone the westerlies make the eastern side warmer (UPSC 2021: both correct). Fog off Newfoundland, where warm and cold currents meet, is in Chapter 10.
NCERT exercise — answer outlines
Try each question yourself first, then open the outline to compare. The multiple-choice questions are in the self-check below.
What are waves? (30 words)
Waves are energy, not water, moving across the ocean surface. Water particles move only in small circles; the wave train moves on and releases its energy on the shore.
Where do waves in the ocean get their energy from? (30 words)
Mainly from the wind pushing against the water. Wave size depends on wind strength, how long it blows and the area over which it blows in one direction.
What are tides? (30 words)
The periodic rise and fall of sea level, once or twice a day, caused mainly by the gravitational pull of the moon and, to a lesser extent, the sun, together with centrifugal force.
How are tides caused? (30 words)
The moon's gravity pulls water into a bulge on the near side; centrifugal force raises a second bulge on the far side. The earth rotates through both; the sun strengthens (spring) or weakens (neap) them.
How are tides related to navigation? (30 words)
Tides are predictable, so sailors plan around them. High tide lets ships cross shallow bars into river and estuary harbours (Kolkata–Diamond Harbour, Kandla); tidal currents help or hinder ships.
How do currents affect the temperature? How does it affect the temperature of coastal areas in the N.W. Europe? (150 words)
General: currents carry heat between latitudes. Warm currents raise the temperature of cold areas; cold currents lower it in warm areas.
Patterns: cold currents on west coasts in low and middle latitudes → cool, foggy, arid coasts with small ranges; warm currents on east coasts → warm, rainy climates; warm currents on west coasts in high latitudes → mild marine climates. Isotherms bend accordingly (Chapter 8, 12).
NW Europe: the Gulf Stream continues as the North Atlantic Drift; westerlies carry its warmth inland. Winters are far milder than elsewhere at 60°–70°N, Norway's ports stay ice-free, annual range is small, rain falls all year (Cfb climate). Compare Labrador at the same latitude, chilled by the cold Labrador current.
Diagram: sketch of the North Atlantic gyre.
Patterns: cold currents on west coasts in low and middle latitudes → cool, foggy, arid coasts with small ranges; warm currents on east coasts → warm, rainy climates; warm currents on west coasts in high latitudes → mild marine climates. Isotherms bend accordingly (Chapter 8, 12).
NW Europe: the Gulf Stream continues as the North Atlantic Drift; westerlies carry its warmth inland. Winters are far milder than elsewhere at 60°–70°N, Norway's ports stay ice-free, annual range is small, rain falls all year (Cfb climate). Compare Labrador at the same latitude, chilled by the cold Labrador current.
Diagram: sketch of the North Atlantic gyre.
What are the causes of currents? (150 words)
Primary forces: (1) solar heating — warm water expands; the sea is ~8 cm higher at the equator, so water flows down the gradient; (2) wind — friction drags surface water (trades westward, westerlies eastward); (3) gravity — pulls water down the ‘pile’; (4) Coriolis force — deflects flow right in the NH, left in the SH, creating gyres.
Density differences: cold and salty water is denser and sinks at high latitudes, driving deep currents (90% of water); warm surface water flows poleward to replace it.
Other influences: shape of coastlines and ocean basins; monsoon winds reversing currents in the north Indian Ocean; pressure belts.
Result: clockwise gyres in the NH, anticlockwise in the SH; warm currents on east coasts, cold on west coasts in low and middle latitudes.
Diagram: an idealised ocean basin with its gyre.
Density differences: cold and salty water is denser and sinks at high latitudes, driving deep currents (90% of water); warm surface water flows poleward to replace it.
Other influences: shape of coastlines and ocean basins; monsoon winds reversing currents in the north Indian Ocean; pressure belts.
Result: clockwise gyres in the NH, anticlockwise in the SH; warm currents on east coasts, cold on west coasts in low and middle latitudes.
Diagram: an idealised ocean basin with its gyre.
What to remember
Numbers
Breeze that starts ripples2 knots or less
Wave amplitude½ of wave height
Bay of Fundy tidal bulge15–16 m (highest in the world)
Bay of Fundy rise (NCERT estimate)~240 cm per hour
Spring tidestwice a month — new and full moon
Spring → neap interval~7 days
Moon's pull vs sun'smore than twice as strong
Perihelion / aphelion~3 January / ~4 July
Sea level at the equator vs mid-latitudes~8 cm higher
Surface currents~10% of ocean water, upper 400 m
Deep-water currents~90% of ocean water
Surface current speedup to / over 5 knots
Deep current speedunder 0.5 knots
Tidal power plant in India (NCERT)3 MW, Durgaduani, Sunderbans
One-liners
- Waves move energy; currents move water.
- Tides: moon (mainly) + sun + centrifugal force.
- Spring = in line (new/full moon); neap = right angles (quarters).
- Perigee is the moon's closest point; perihelion is the earth's closest point to the sun.
- Ebb = falling tide; flood (flow) = rising tide.
- Warm currents on east coasts, cold on west coasts (low and middle latitudes).
- NH gyres clockwise; SH gyres anticlockwise.
- Fishing grounds where warm and cold currents meet.
Traps to avoid
- Neap tides are not at new moon — they are at the first and third quarters.
- Spring tides occur at both full and new moon.
- A surge (weather-driven) is not a tide.
- In high northern latitudes the rule flips: warm currents on west coasts, cold on east coasts.
- The equatorial counter-current flows east.
- Earth's revolution does not drive ocean currents; rotation (Coriolis) does.
- Labrador, Canaries, California, Humboldt, Benguela, Falkland, Oyashio, West Australian are cold.
- Fundy arithmetic: 1,440 cm is 14.4 m, not 15–16 m.
- Perihelion's effect on tides is small, though NCERT says ‘much greater’.
How to strategise
Prelims — what UPSC asks
- Tides are a favourite: causes (1986, 2015), spring tides from diagrams (1988, 1999), neap tides (1991, 2001), tidal bores and gulfs (2004), tidal ports and the uses of tides (1995, 2000).
- Currents: match currents to coasts (1985), warm or cold (1989), causes (2002, 2012), the equatorial counter-current (2015), Indian Ocean monsoon drift (1997), and which side of the ocean is warmer (2021).
- Productivity: fishing grounds where currents meet (2013); upwelling brings nutrients (2011).
- Learn the world map of currents: for each ocean, the gyre direction, the warm current on the western side and the cold current on the eastern side.
Mains — where it appears and how to answer
- GS1: factors behind the origin of ocean currents and their effect on climate, fishing and navigation (2015); forces that influence currents and their role in the world's fishing industry (2022); ocean currents vs water masses — impacts on marine life and coasts (2019).
- Answer frame: forces (solar heating, wind, gravity, Coriolis, density) → pattern (gyres, warm east and cold west coasts) → effects (climate examples: NW Europe, Atacama; fog; fishing grounds: Grand Banks, Dogger Bank, Japan, Peru upwelling; navigation) → a labelled world sketch.
- Tides for GS3: tidal energy potential (Gulf of Kachchh, Khambhat, Sunderbans), tidal ports, and the difference between tides, storm surges and tsunamis in disaster answers.
Self-check
Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.
1. Upward and downward movement of ocean water is known as the:
2. Spring tides are caused:
3. The distance between the earth and the moon is minimum when the moon is in:
4. The earth reaches its perihelion in:
5. Neap tides occur when:
6. Which of these is a cold current?
7. The world's richest fishing grounds are mainly found where:
UPSC questions from this chapter
Open any question to attempt it in the Question bank — your attempt is saved to your progress.