Oceanography — Practice Questions
UPSC Prelims-pattern practice questions on oceanography — ocean-floor relief, tides, currents, UNCLOS maritime zones and ocean features, with explanations.
Questions
These are original UPSC-pattern practice questions. Attempt each one before revealing the answer.
Arrange the following features of the ocean floor in order from the coast towards the deep ocean:
- Continental slope
- Abyssal plain
- Continental shelf
- Continental rise
Select the correct answer using the code given below.
Solution
From the coast outward: continental shelf (gently sloping, shallow) → continental slope (steep) → continental rise (sediment apron at the foot of the slope) → abyssal plain (flat deep-sea floor). So 3-1-4-2.
Option D is the common slip of putting the abyssal plain before the rise.
Answer: A
Consider the following statements about tides:
- Spring tides occur at new moon and full moon.
- Neap tides occur when the Sun and the Moon are at right angles to each other with respect to the Earth.
- The Sun’s tide-generating force is greater than that of the Moon.
Which of the statements given above is/are correct?
Solution
- Statement 1 — correct. At new and full moon the Sun, Moon and Earth are in a line and their pulls reinforce each other.
- Statement 2 — correct. At the first and third quarters they pull at right angles, partly cancelling — neap tides.
- Statement 3 — wrong. Tide-generating force depends strongly on distance; the Moon is so much closer that its effect is greater than the Sun’s.
Answer: B
Consider the following pairs:
| Ocean current | Ocean |
|---|---|
| 1. Kuroshio | North Pacific |
| 2. Agulhas | South Atlantic |
| 3. Canary | North Atlantic |
| 4. Humboldt | South Pacific |
How many of the pairs given above are correctly matched?
Solution
- Kuroshio — North Pacific (correct): warm current off Japan.
- Agulhas — South Atlantic (wrong): the Agulhas is a warm current of the Indian Ocean, along south-eastern Africa. The cold current of the South Atlantic off south-western Africa is the Benguela.
- Canary — North Atlantic (correct): cold current off north-west Africa.
- Humboldt — South Pacific (correct): cold current off Peru and Chile.
So three pairs are correct.
Answer: C
Consider the following statements regarding maritime zones under the United Nations Convention on the Law of the Sea (UNCLOS):
- The territorial sea extends up to 12 nautical miles from the baseline.
- The contiguous zone extends up to 24 nautical miles from the baseline.
- In its Exclusive Economic Zone, a coastal state enjoys full sovereignty, including the right to deny overflight to foreign aircraft.
Which of the statements given above is/are correct?
Solution
- Statements 1 and 2 — correct.
- Statement 3 — wrong. In the EEZ (up to 200 nautical miles) the coastal state has sovereign rights over resources — fishing, oil, gas, minerals, energy — but other states retain freedom of navigation and overflight and of laying submarine cables. Full sovereignty (including airspace) extends only over the territorial sea.
Answer: D
Which one of the following best describes a guyot?
Solution
A guyot is a flat-topped seamount. It was once a volcanic island whose top was planed off by waves; as the ocean floor moved away from the hotspot or ridge and subsided, it sank below the surface.
- Option B describes a trench (for example, the Mariana Trench).
- Option C describes an atoll (for example, the Lakshadweep islands).
- Option D describes a submarine canyon.
Answer: A
Mains
Explain the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). How do they together influence the Indian summer monsoon?
Solution
Introduction: The Indian monsoon is shaped not only by land–sea heating contrasts but also by ocean–atmosphere oscillations far from India. ENSO in the Pacific and the IOD in the Indian Ocean are the two most important.
Body:
- ENSO: in normal years strong trade winds pile warm water near Indonesia, with cold upwelling off Peru and a Walker circulation rising over the western Pacific. In El Niño years the trades weaken, warm water spreads east, and the rising limb of the Walker circulation shifts towards the central Pacific, often bringing subsiding, drier air over the Indian region. La Niña strengthens the normal pattern. The Southern Oscillation is the accompanying pressure see-saw between Tahiti and Darwin.
- IOD: a difference in sea-surface temperature between the western and eastern Indian Ocean. A positive IOD (warmer west) enhances convection and moisture supply over the western Indian Ocean and tends to support the monsoon; a negative IOD tends to weaken it.
- Interaction: a positive IOD can partly offset an El Niño; an El Niño with a negative IOD raises the risk of drought. Hence not every El Niño year is a drought year.
- Implications: agriculture, food inflation, reservoir levels and hydropower; IMD’s seasonal forecasts track both indices.
Conclusion: ENSO and the IOD act as remote controls on India’s rainfall. Better ocean observation and coupled forecasting are central to drought preparedness and climate-resilient agriculture.