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Ocean Currents, Upwelling and Climate: A Conceptual Guide — MCQs with Answers

Test what you know about Ocean Currents, Upwelling and Climate: A Conceptual Guide with 10 UPSC Prelims-style questions. Try each one first, then tap “Show answer” for the correct option and its explanation.

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  1. Q1. A straight western coast of a continent lies at 30°N, with the ocean to its west. A steady wind blows towards the south. Under ideal Ekman conditions, which combination is expected near the coast?

    1. Eastward transport and upwelling
    2. Westward transport and downwelling
    3. Westward transport and upwelling
    4. Eastward transport and downwelling
    Show answer

    Correct answer: (C) Westward transport and upwelling

    Explanation

    Correct Answer: (C). In the Northern Hemisphere, net Ekman transport is to the right of the wind. Right of a southward wind is westward, which is offshore in this scenario. Surface-water removal permits replacement from below. Eastward transport misapplies the directional rule; downwelling requires coastal accumulation rather than offshore removal.

  2. Q2. Consider the following statements about subtropical gyres: 1. A western boundary current can flow along the eastern coast of a continent. 2. Western boundary currents are generally broader and slower than eastern boundary currents. 3. A cold horizontal current establishes that local coastal upwelling is occurring. Which of the statements given above is/are correct?

    1. 1 only
    2. 1 and 2 only
    3. 2 and 3 only
    4. 1 and 3 only
    Show answer

    Correct answer: (A) 1 only

    Explanation

    Correct Answer: (A). The boundary is named relative to the ocean basin, making statement 1 correct. Western boundary currents are generally narrower and faster, reversing statement 2. Cold water may arrive horizontally from another region, so its presence does not establish the vertical replacement required for upwelling in statement 3.

  3. Q3. Two surface seawater samples are at the same pressure. Sample P is colder but less saline than sample Q. No numerical temperature or salinity values are supplied. Which inference about their densities is justified?

    1. P is denser because temperature determines the ranking
    2. Q is denser because salinity determines the ranking
    3. Their densities are equal because the effects oppose each other
    4. Their density ranking requires the sizes of both differences
    Show answer

    Correct answer: (D) Their density ranking requires the sizes of both differences

    Explanation

    Correct Answer: (D). Cooling generally raises seawater density, whereas reduced salinity lowers it. These effects compete in sample P. Opposite signs do not imply equal magnitudes, and neither variable can be assumed to dominate without values. Hence the density ranking cannot be established from the qualitative information supplied.

  4. Q4. Consider the following pairs: 1. Gulf Stream — Western boundary of the North Atlantic subtropical gyre 2. Kuroshio — Eastern boundary of the North Pacific subtropical gyre 3. Canary Current — Eastern boundary of the North Atlantic subtropical gyre 4. California Current — Western boundary of the North Pacific subtropical gyre How many of the pairs given above are correctly matched?

    1. Only one
    2. Only two
    3. Only three
    4. All four
    Show answer

    Correct answer: (B) Only two

    Explanation

    Correct Answer: (B). Pairs 1 and 3 are correct. The Gulf Stream and Canary Current occupy opposite boundaries of the North Atlantic subtropical gyre. Kuroshio is a western, not eastern, boundary current; California is an eastern, not western, boundary current. Locating the ocean basin avoids confusing its edges with continental coasts.

  5. Q5. Consider the following statements: Statement-I: Under westward trade winds, equatorial surface divergence can favour upwelling. Statement-II: The Coriolis parameter changes sign across the equator, allowing opposite poleward Ekman transports on its northern and southern sides. Which one of the following is correct?

    1. Both are correct, but II does not explain I
    2. Both are correct, and II explains I
    3. I is correct, but II is incorrect
    4. I is incorrect, but II is correct
    Show answer

    Correct answer: (B) Both are correct, and II explains I

    Explanation

    Correct Answer: (B). Westward winds produce northward transport on the northern side and southward transport on the southern side. Their separation removes surface water from the equatorial region, permitting upward replacement. Statement II therefore explains statement I. This does not require a nonzero or maximum Coriolis parameter exactly at the equator.

  6. Q6. Consider the following statements about ocean density: 1. Sea-ice formation tends to increase the salinity of surrounding seawater through salt rejection. 2. Freshwater addition tends to reinforce the density increase caused by surface cooling. 3. Density comparisons across different depths require attention to pressure. Which of the statements given above are correct?

    1. 1 and 2 only
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Show answer

    Correct answer: (C) 1 and 3 only

    Explanation

    Correct Answer: (C). Salt rejected during sea-ice formation raises surrounding salinity, while pressure must be considered when comparing different depths. Statements 1 and 3 are correct. Freshwater generally lowers salinity and density, other conditions unchanged, so it can oppose the density effect of cooling rather than reinforce it.

  7. Q7. Consider the following statements regarding the AMOC and the Gulf Stream: 1. The AMOC includes an upper-ocean northward flow and a colder deep southward return. 2. The Gulf Stream also participates in wind-driven subtropical circulation. 3. Weakening of the AMOC implies cessation of the entire North Atlantic surface circulation. Which of the statements given above are correct?

    1. 1 and 2 only
    2. 1 and 3 only
    3. 2 and 3 only
    4. 1, 2 and 3
    Show answer

    Correct answer: (A) 1 and 2 only

    Explanation

    Correct Answer: (A). The AMOC describes overturning with flows at different depths, while the Gulf Stream also belongs to the wind-driven gyre. Statements 1 and 2 are correct. Because these systems are related but not identical, an overturning change does not establish the complete loss of wind-driven surface circulation asserted in statement 3.

  8. Q8. In a hypothetical tropical ocean region, sunlight remains abundant, the thermocline deepens and upward nutrient supply declines. Which outcome and explanation are most consistent with these conditions?

    1. Higher phytoplankton production because the illuminated surface remains warm
    2. Higher phytoplankton production because the thermocline stores nutrients deeper
    3. Unchanged phytoplankton production because sunlight is not reduced
    4. Lower phytoplankton production because nutrients can become limiting
    Show answer

    Correct answer: (D) Lower phytoplankton production because nutrients can become limiting

    Explanation

    Correct Answer: (D). Light and nutrients jointly support phytoplankton growth. Abundant sunshine cannot compensate for insufficient nutrient delivery to the illuminated layer. A deeper thermocline does not make deep nutrients more accessible merely by storing them below. The scenario therefore supports reduced production, not a guarantee of higher or unchanged productivity.

  9. Q9. Consider the following statements about circulation rules: 1. Northern Hemisphere subtropical gyres generally rotate clockwise, but its subpolar gyres can rotate anticlockwise. 2. A 90-degree net Ekman transport means each water parcel in the affected layer moves at 90 degrees to the wind. 3. Coriolis deflection is measured relative to the direction of motion, not a fixed compass direction. Which of the statements given above are correct?

    1. 1 and 2 only
    2. 1 and 3 only
    3. 2 and 3 only
    4. 1, 2 and 3
    Show answer

    Correct answer: (B) 1 and 3 only

    Explanation

    Correct Answer: (B). The gyre rule must retain its subtropical qualifier, and right or left is relative to motion. Statements 1 and 3 are correct. Ekman transport sums motion through a layer whose constituent flows differ in direction and speed; it does not assign the net angle to every parcel as statement 2 does.

  10. Q10. A coastal survey detects high surface chlorophyll following nutrient-rich upwelling. Which inference is best supported without additional fish-stock or fishing-pressure data?

    1. Conditions support phytoplankton abundance, but sustainable catch remains undetermined
    2. Sustainable fish catch has increased in proportion to chlorophyll
    3. Fish-stock abundance can be obtained directly from the chlorophyll value
    4. The existing fishing effort can rise without affecting stock renewal
    Show answer

    Correct answer: (A) Conditions support phytoplankton abundance, but sustainable catch remains undetermined

    Explanation

    Correct Answer: (A). Chlorophyll indicates phytoplankton abundance and helps connect nutrient delivery with the base of the food web. It is not a direct fish count or a measure of sustainable harvest. Food-web transfers, habitat and fishing pressure remain relevant, so proportional catch increases or safe effort expansion cannot be inferred.

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