The Ocean Currents
1. 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 influences the ocean currents?
(a) 1 and 2
(b) 1, 2 and 3
(c) 1 and 4
(d) 2, 3 and 4
[I.A.S. (Pre) 2012]
Ans. (b) 1, 2 and 3
- The ocean has a steady flow that comes from the Earth’s rotation, the wind, temperature, salinity, air pressure, and differences in the seawater’s density.
- The Earth’s revolution does not have an effect on ocean currents, so answer (b) is the right choice.
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2. 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.
Which of these statements are correct?
(a) 1 and 2
(b) 2, 3 and 4
(c) 1, 3 and 4
(d) 1, 2, 3 and 4
[I.A.S. (Pre) 2002]
Ans. (d) 1, 2, 3 and 4
- Ocean water moving in a particular direction is referred to as an ocean current.
- This is usually caused by the wind. If the wind is weak, the surface water will usually be in motion.
- In colder regions, warm currents (Gulf Stream) and in hotter regions, cold currents help to keep the temperature stable.
- Ocean currents are also impacted by the shape of the ocean, in addition to the prevailing winds and the Earth’s rotation.
- Thus, statement 4 is also correct.
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3. Which one of the following factors is responsible for the change in the regular direction of the ocean currents in the Indian Ocean?
(a) The Indian Ocean is half an Ocean
(b) The Indian Ocean has Monsoon drift
(c) The Indian Ocean is a land-locked ocean
(d) The Indian Ocean has greater variation in salinity
[I.A.S. (Pre) 1997]
Ans. (b) The Indian Ocean has Monsoon drift
- The Indian Ocean’s currents are not the same as the Pacific and Atlantic Oceans.
- The land and monsoon winds have a big effect on the Indian Ocean’s currents.
- The flow of the current changes twice in the northern part of the Indian Ocean because of the North-East and South-West monsoon winds, but currents in the Southern Indian Ocean are more predictable.
- Therefore, option (b) is the correct answer.
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4. Agulhas current flows in –
(a) The Indian Ocean
(b) The Pacific Ocean
(c) North Atlantic Ocean
(d) South Atlantic Ocean
[R.A.S./R.T.S. (Pre) 1999]
Ans. (a) The Indian Ocean
- The Agulhas Current is a warm water current that flows in the South Indian Ocean.
- It starts as a branch of the South Equatorial Indian Ocean current that flows through the southeast coast of Mozambique and is known as the Mozambique Current.
- This current then turns south and meets with a branch of the South Equatorial Current that flows east of Madagascar.
- The combination of these two currents is known as the Agulhas Current, which flows to the southernmost end of Africa before turning east and mixing with the West Wind Drift.
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5. Which of the following is not a cold ocean current?
(a) Canaries
(b) Humboldt
(c) Oyashio
(d) Agulhas
[U.P.P.C.S. (Pre) 2017]
Ans. (d) Agulhas
- The Agulhas current is a warm water current in the South Indian Ocean.
- It is made when the South Equatorial Indian Ocean current moves south along the Mozambique coast and meets with a branch of the South Equatorial current near Madagascar.
- This combination is known as the Agulhas current.
- It moves down to the bottom of Africa and then switches directions to go east, mixing with the West wind drift.
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6. Which of the following ocean currents is associated with the Indian Ocean?
(a) Florida current
(b) Canary current
(c) Agulhas current
(d) Kurile current
[U.P. P.C.S. (Pre) 2020]
Ans. (c) Agulhas current
- The Agulhas Current is an ocean current that is connected to the Indian Ocean and flows down the east coast of Africa from the 27th to the 40th parallel south.
- It is the western boundary current of the South Indian Ocean.
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7. Which of the following is a warm current?
(a) Falkland Current
(b) Brazil Current
(c) Labrador Current
(d) Canary Current
[U.P. R.O./A.R.O. (Mains) 2017]
Ans. (b) Brazil Current
- There are two different types of ocean currents :
- Warm currents :
- The Brazil current
- Gulf stream
- Kuroshio current
- Cold currents :
- The Falkland current
- Labrador current
- Canary current
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8. The country benefiting the most from the North Atlantic Drift is :
(a) Poland
(b) Portugal
(c) Norway
(d) Nigeria
[R.A.S./R.T.S.(Pre) 1999]
Ans. (c) Norway
- Near 45° north latitude and 45° west meridian, the Northern Atlantic current moves warm water from the Gulf Stream towards Europe.
- Norway, which is in the subpolar region, gets the most benefit from this current.
- In the winter, it helps to prevent the expansion of ice over most of Europe, earning it the nickname ‘Blanket of Europe’.
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9. Which one of the following is a cold current of the South Atlantic Ocean?
(a) Canary current
(b) Benguela current
(c) Agulhas current
(d) Brazil current
[U.P.P.C.S. (Pre) 2005]
Ans. (b) Benguela current
- The Benguela current is the only cold water current in the South Atlantic Ocean.
- It moves northward along the west side of South Africa and eventually joins with the South Equatorial current.
- Option B is the correct answer.
- The other currents mentioned are :
- The Brazil Current (warm water current that flows north to south along the east coast of Brazil).
- The Canary Current (cold water current that moves north to south along the west coast of northwest Africa).
- The Agulhas Current (warm water current that moves north to south in the South Indian Ocean).
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10. Which one of the following Oceanic currents is not associated with the Pacific Ocean?
(a) Canaries
(b) Kuroshio
(c) California
(d) Humboldt
[Uttarakhand P.C.S. (Pre) 2016]
Ans. (a) Canaries
- The Canary Current is a cold flow of water that travels south in the North Atlantic Ocean along the western side of northwest Africa.
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11. Which of the following ocean currents does not belong to the Indian Ocean?
(a) Agulhas Current
(b) Mozambique Current
(c) South Indian Ocean Current
(d) Benguela Current
[U.P.P.C.S. (Mains) 2014]
Ans. (d) Benguela Current
- The Agulhas current runs along the western side of the South Indian Ocean and is a warm current.
- Additionally, the Mozambique current is also warm and runs through the Mozambique Channel in the West Indian Ocean.
- In latitudes 40°-45°, the South Indian Ocean current moves through the area.
- The Benguela current is a cold water current that flows along the east coast of the South Atlantic Ocean.
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12. Which one of the following currents does not contribute to forming a complete circle of currents in the South Atlantic Ocean:
(a) Benguela
(b) Brazil
(c) Canary
(d) West wind drift
[U.P.P.C.S. (Pre) 2000]
Ans. (c) Canary
- In the South Atlantic Ocean, there is a pattern of currents that form a complete circle.
- It starts with the South Equatorial current, which hits the Brazil coast and is called the Brazil current.
- The Earth’s rotation causes a disturbance, and the Westwind affects the Brazil current at 40° latitude.
- The Falklands current from the south joins the Brazil current, and together they move east as the South Atlantic current.
- One branch of this current reaches the west coast of South Africa and turns north into the Benguela Current.
- The entire circle of currents flows in an anticlockwise direction.
- The Canary current is not part of this pattern; it is a cold current that flows in the North Atlantic Ocean.
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13. The ocean current differences from the remaining three are:
(a) Banguela
(b) Brazilian
(c) South Equatorial
(d) Peruvian
[R.A.S./R.T.S.(Pre) 1999]
Ans. (d) Peruvian
- Apart from the Peruvian current, all of the other currents mentioned have something to do with the Atlantic Ocean, which forms a loop.
- The Peruvian current is connected to the Southeast Pacific Ocean and is also known as the Humboldt current.
- It’s a cold stream that flows along the west coast of South America.
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14. Which of the following is a cold ocean current :
(a) Peruvian Current (Humboldt Current)
(b) Kuroshio Current
(c) Gulf Stream
(d) Brazil Current
[Jharkhand P.C.S. (Pre) 2003, U.P.P.C.S. (Pre) 1995]
Ans. (a) Peruvian Current (Humboldt Current)
- Apart from the Peruvian current, the other three currents are associated with the Atlantic Ocean, which forms a loop.
- The Peruvian current is associated with the Southeast Pacific Ocean, and it is also called the Humboldt current.
- It is a cold current that runs along the western coastline of South America.
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15. Which of the following is not matched correctly?
(a) Brazil Current – South Atlantic Ocean
(b) Humboldt Current – North Pacific Ocean
(c) Gulf Stream – North Atlantic Ocean
(d) Agulhas Current – Indian Ocean
[U.P. P.C.S. (Pre) 1998]
Ans. (b) Humboldt Current – North Pacific Ocean
- Besides the Peruvian current, the other three currents are all connected to the Atlantic Ocean, which forms a loop.
- The Peruvian current, also known as the Humboldt current, is connected to the Southeast Pacific ocean.
- This cold current follows the west coast of South America.
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16. Gulf Stream is –
(a) a river in the Gulf
(b) an oceanic current
(c) another name of Jet Stream
(d) a surface wind
[44th B.P.S.C. (Pre) 2000, 42nd B.P.S.C. (Pre) 1997]
Ans. (b) an oceanic current
- The Gulf Stream is a strong, warm water flow in the North Atlantic Ocean.
- It starts in the Gulf of Mexico as the Florida Current, then combines with the Antilles Current and passes through Cape Hatteras.
- It then follows the east coast of the United States. Spanish explorer Juan Ponce de Leon first noticed it in 1513.
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17. Match List-I with List-II and select the correct answer using the code given below the Lists :
List-I List-II
A. Gulf Stream 1. Pacific Ocean
B. West Wind Drift 2. A slow eastward movement of water over the zone of westerly wind
C. Peru Current 3. Indian Ocean
D. West Australian Current 4. Warm current
Code :
A B C D
(a) 4 2 1 3
(b) 1 3 4 2
(c) 4 3 1 2
(d) 1 2 4 3
[Jharkhand P.C.S. (Pre) 2013]
Ans. (a) 4 2 1 3
- The correctly matched of List-I and List-II is as follows :
| Gulf Stream |
Warm Current |
| West Wind Drift |
A slow eastward movement of water over the zone of westerly wind |
| Peru Current |
Pacific Ocean |
| West Australian Current |
Indian Ocean |
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18. What explains the eastward flow of the equatorial counter-current?
(a) The Earth’s rotation on its axis
(b) Convergence of the two equatorial currents
(c) Difference in salinity of water
(d) Occurrence of the Belt of Calm near the equator
[I.A.S. (Pre) 2015]
Ans. (a) The Earth’s rotation on its axis
- Two currents flow eastward from the equator, the north equatorial current and the south equatorial current.
- In between these two, an equatorial counter current flows westward.
- The piling up of water from the two equatorial currents causes the counter current.
- This is caused by the earth rotating on its axis.
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Salinity of the Ocean
1. Which one of the following denotes water salinity gradient?
(a) Thermocline
(b) Halocline
(c) Pycnocline
(d) Chemocline
[U.P.P.C.S. (Pre) (Re-Exam) 2015]
Ans. (b) Halocline
- Halocline is an area in the ocean where the saltiness of the water changes quickly as you go deeper.
- It is a type of water that has a different salinity level at different depths.
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2. Main Source of Salinity of the Sea is –
(a) Rivers
(b) Land
(c) Wind
(d) Ash ejected from the Volcano
[53rd to 55th B.P.S.C. (Pre) 2011]
Ans. (b) Land
- The main cause of the saltiness of the ocean is from the land.
- Rivers bring different kinds of salt to the ocean, but other things like evaporation, wind, river water, rain, ocean currents, and volcanoes also affect the saltiness of the ocean.
- The average saltiness of the ocean is about 35Å.
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3. Which one of the following salts contributes maximum to the salinity of sea water :
(a) Calcium sulphate
(b) Magnesium chloride
(c) Magnesium sulphate
(d) Sodium chloride
[U.P.P.C.S. (Pre) 2000]
Ans. (d) Sodium chloride
- In 1884, William Dittmar created a document during the Challenger expedition about the chemical makeup of the ocean.
- The report showed that there were 27 different types of salt in the ocean, with 7 being the most common.
- These 7 were:
| Salt |
Salinity (Å) |
Percentage (%) |
| Sodium Chloride |
27.213 |
77.8 |
| Magnesium Chloride |
3.807 |
10.9 |
| Magnesium Sulphate |
1.658 |
4.7 |
| Calcium Sulphate |
1.260 |
3.6 |
| Potassium Sulphate |
0.863 |
2.5 |
| Calcium Carbonate |
0.123 |
0.3 |
| Magnesium Bromide |
0.076 |
0.2 |
|
35 |
100 |
- The average saltiness of oceans is usually around 35 parts per thousand, and Sodium Chloride is the main component that makes up this saltiness.
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4. The highest salinity is found in :
(a) Dead sea
(b) Red sea
(c) Great Salt Lake in the U.S.A.
(d) Lake Van in Turkey
[U.P.P.C.S. (Pre) 1995]
Ans. (d) Lake Van in Turkey
- Van Lake in Turkey has the highest salt content out of all the lakes and seas mentioned in the question, which is 330Å.
- Salinity in the Dead Sea = 238Å
- Salinity in the Red Sea = 36-41Å
- Salinity in Great Salt Lake = 220Å
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5. The highest amount of salinity is found in –
(a) Pacific Ocean
(b) Indian Ocean
(c) Mediterranean Sea
(d) Dead Sea
[M.P.P.C.S. (Pre) 2015, Uttarakhand P.C.S. (Mains) 2006]
Ans. (d) Dead Sea
- Salinity in the Dead Sea is 238Å.
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6. World’s most saline Ocean/Lake is –
(a) Caspian Sea
(b) Great Salt Lake
(c) Dead Sea
(d) Lake Van
[R.A.S./R.T.S. (Pre) 1997]
Ans. (d) Lake Van
- The Dead Sea is the saltiest lake in the world, with a salt content of around 34%.
- It’s situated in the Middle East between Israel and Jordan.
- Its surface is 1,292 feet below sea level, and its edges are the lowest place on Earth.
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7. Which of the following seas has the highest salinity?
(a) Caspian Sea
(b) Mediterranean Sea
(c) Red Sea
(d) Dead Sea
[U.P.P.C.S.(Pre) 2012]
Ans. (*)
- The Red Sea has the highest saltiness of any sea, with 36 to 41 parts per thousand.
- The Mediterranean Sea has a saltiness of 37 to 39 parts per thousand.
- The Dead Sea has an even higher saltiness than the Red Sea and Mediterranean, but it is considered a lake.
- The Caspian Sea is also a lake.
- If all the options are counted as seas, the Dead Sea has the highest saltiness and would be the saltiest.
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8. Which of the following seas has the highest average salinity?
(a) Black Sea
(b) Yellow Sea
(c) Mediterranean Sea
(d) Dead Sea
(e) None of the above/More than one of the above
[60th to 62nd B.P.S.C. (Pre) 2016]
Ans. (d) Dead Sea
- The Dead Sea has the most salt of all the options listed, with an average salinity of 238Å.
- However, Assal Lake has the most salt of any lake in the world, with an average
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9. When the density in the sea increases, then –
(a) Salinity and depth decreases
(b) Salinity increases but depth decreases
(c) Both salinity and depth increases
(d) Salinity decreases and depth increases
[U.P. P.C.S. (Pre) 1990]
Ans. (b) Salinity increases but depth decreases
- When the sea’s water becomes more dense, it means that its saltiness has increased.
- The saltiness can be divided into two types:
- Horizontal
- Vertical
- So far, there is no exact pattern for the vertical saltiness in the ocean.
- In some places, the saltiness increases as the depth increases, but in other places, the saltiness decreases as the depth increases.
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10. Where is the Great Salt Lake located?
(a) Iran
(b) U.S.A.
(c) India
(d) Turkey
[Uttarakhand U.D.A./L.D.A. (Mains) 2006, 2007]
Ans. (b) U.S.A.
- The Great Salt Lake is located in the state of Utah in the USA.
- Its salt content is 220Å.
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11. The average salinity of water of Arabian Sea is-
(a) 25 ppt
(b) 35 ppt
(c) 45 ppt
(d) 55 ppt
[53rd to 55th B.P.S.C. (Pre) 2011]
Ans. (b) 35 ppt
- In the Indian Ocean between 0 and 10 degrees latitude, the salinity is 35.14 Å.
- In the Bay of Bengal, the salinity decreases to 30 Å.
- In the Arabian Sea, the salinity is higher at 36 Å because of the dry weather causing more vaporization and less water from rivers, which makes option (b) the correct answer.
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High Tide, Low Tide
1. What are the causes of high-tide low tide formation in the oceans ?
(a) Due to the effect of the sun
(b) Due to the rotation of the Earth
(c) Due to the combined effect of sun and the moon
(d) Due to Gravitation, Centripetal force and the centrifugal force
[U.P.P.C.S. (Pre) 1991]
Ans. (d) Due to Gravitation, Centripetal force and the centrifugal force
- The changing tides are caused by the pull of gravity between the Earth and the Moon.
- The Earth’s gravity keeps the water levels the same all over the planet, but the Moon’s gravity disrupts this balance and causes the water in the hemisphere facing the Moon to move faster.
- When the Moon’s force is stronger, it creates high tides.
- When the Earth’s centrifugal force is stronger, it creates low tides.
- These high and low tides happen twice a day.
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2. Tides occur in oceans and seas due to which among the following?
1. Gravitational force of sun
2. Gravitational force of Moon
3. Centrifugal force of Earth
Select the correct answer using the codes given below:
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
[I.A.S. (Pre) 2015]
Ans. (d) 1, 2 and 3
- The Earth and Moon’s gravity affects the ocean’s water levels.
- The Moon’s gravitational pull makes the water in the hemisphere facing it move faster, which causes high tides.
- When the Earth’s centrifugal force is stronger than the Moon’s pull, low tides (indirect high tides) occur.
- The Earth experiences high and low tides twice every day.
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3. The cause of producing indirect high tide is –
(a) Gravitational force of the Moon
(b) Gravitational force of the Sun
(c) Centrifugal force of the Earth
(d) Gravitational force of the Earth
[R.A.S./R.T.S. (Pre) 1999]
Ans. (c) Centrifugal force of the Earth
- The gravitational pull of the moon and sun causes indirect high tides.
- The moon’s gravitational pull creates a force that makes the Earth and its water bulge out on the sides closest and farthest from the moon.
- These bulges are what create high tides.
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4. Statement (A): During the times of neap tide, hightide is below normal and low-tide is above normal.
Reason (R): Neap tide occurs during the new moon instead of full-Moon.
Choose the correct answer using following options –
(a) (A) and (R) both are correct, and (R) is correct explanation of (A)
(b) (A) and (R) both are correct, and (R) is not correct explanation of (A)
(c) (A) is correct, but (R) is wrong
(d) (A) is wrong, but (R) is correct
[I.A.S. (Pre) 1998]
Ans. (c) (A) is correct, but (R) is wrong.
- At neap-tides, high-tide is 20% lower than usual and low-tide is higher than usual.
- Neap-tides don’t happen at the same time as spring-tides, but on the 7th or 8th day after New-moon or full-moon.
- Statement (A) is correct, but the reason (R) is incorrect.
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5. Spring Tide occurs :
(a) When the Sun the Earth and Moon are in a straight line
(b) When the Sun and Moon make a right angle
(c) When a strong wind blows
(d) When the night is very cold
[U.P.P.C.S. (Pre) 1999]
Ans. (a) When the Sun the Earth and Moon are in a straight line
- At neap-tides, the high-tide is 20% less than usual, and the low-tide is higher than usual.
- Neap-tides don’t happen at the same time as spring-tides, which are at the new and full moons; instead, they happen seven or eight days later.
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6. The high tide in the Ocean is caused by
(a) Earthquake
(b) Sun
(c) Stars
(d) Moon
[47th B.P.S.C. (Pre) 2005]
Ans. (d) Moon
- The ocean’s tide is highest on the day of the full moon and lowest on the 7th and 8th day after the full or new moon.
- This is because the moon is closer to the Earth than other stars, so its gravitational pull has a greater effect.
- The moon’s power to cause tides is 2.17 times greater than the sun’s.
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The Oceanic Trenches
1. Match List I with List II and select the correct answer using the code given below in the lists.
List- I List- II
(Oceanic Trench) (Location)
A. Aleutian 1. Indian Ocean
B. Kermadec 2. North Pacific
C. Sunda 3. South pacific
D. S. Sandwich 4. South Atlantic Ocean
Code :
A B C D
(a) 2 4 1 3
(b) 2 3 1 4
(c) 1 3 2 4
(d) 1 4 2 3
[I.A.S. (Pre) 2000]
Ans. (b) 2 3 1 4
- Trenches and Deeps found in the Oceans asked in the question are as follows –
| List- I (Oceanic Trench) |
List- II (Location) |
| Aleutian |
North Pacific Ocean |
| Kermadec |
South Pacific Ocean |
| Sunda |
Indian Ocean |
| S. Sandwich |
South Atlantic Ocean |
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2. Match List-I with List-II and select the correct answer from the codes given below :
List-I List-II
(Ocean) (Deepest Point)
A. Pacific Ocean 1. Java Trench
B. Atlantic Ocean 2. Eurasian Basin
C. Indian Ocean 3. Mariana Trench
D. Arctic Ocean 4. Puerto Rico Trench
Code :
A B C D
(a) 4 3 2 1
(b) 3 4 1 2
(c) 1 3 4 2
(d) 2 4 3 1
[U.P. P.C.S. (Mains) 2017]
Ans. (b) 3 4 1 2
| List-I (Ocean) |
List-II (Deepest Point) |
| Pacific Ocean |
Mariana Trench |
| Atlantic Ocean |
Puerto Rico Trench |
| Indian Ocean |
Java Trench |
| Arctic Ocean |
Eurasian Basin |
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3. Which is the world’s deepest trench?
(a) Northern
(b) Challenger
(c) Manhattan
(d) Richards
[U.P.P.C.S. (Pre) 1991]
Ans. (b) Challenger
- The Mariana trench is in the Pacific Ocean, near the Mariana Islands.
- It is shaped like a crescent.
- It is the deepest part of the ocean, which was named Challenger-Deep after the British exploration vessel HMS Challenger-ii.
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4. Which one of the following is the deepest oceanic trench?
(a) Tonga
(b) Mariana
(c) Puerto Rico
(d) Izu-Bonin
[U.P.P.C.S. (Mains) 2015]
Ans. (b) Mariana
- The Mariana Trench is located in the Pacific Ocean, near the Mariana Islands, in a curved shape.
- It is home to the deepest area on Earth, called Challenger-Deep, which was named after the British vessel HMS Challenger-ii.
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5. In which one of the following oceans Diamantina Trench is situated?
(a) Pacific Ocean
(b) Atlantic Ocean
(c) Indian Ocean
(d) Arctic Ocean
[I.A.S. (Pre) 2006]
Ans. (c) Indian Ocean
- The Diamantina Trench is an area in the Indian Ocean located 1125 kilometers southwest of the Perth Basin.
- It is sometimes referred to as the Diamantina fracture zone.
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