Which of the following factors modify oceanic currents ?
(A) Shape of Coastline
(B) Seasonal Variations
(C) Revolution of the earth
(D) Bottom Reliefs
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Question

Which of the following factors modify oceanic currents ? 
(A) Shape of Coastline 
(B) Seasonal Variations 
(C) Revolution of the earth 
(D) Bottom Reliefs
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Accepted Answer

Here's a detailed explanation supporting Option 2 as the correct answer:

**Why Option 2: (A), (B) and (D) is Correct**

Oceanic currents are complex systems influenced by a variety of factors. Option 2, which includes the Shape of Coastline (A), Seasonal Variations (B), and Bottom Reliefs (D), accurately identifies key modifiers of these currents.

*   **Shape of Coastline (A):** The shape of coastlines directly influences the direction and flow of oceanic currents. When a current encounters a landmass, it is deflected. This deflection can cause the current to split, change direction, or form eddies. The specific shape of the coastline determines the precise nature of this deflection. For example, a sharp headland will cause a more abrupt change in direction than a gently sloping coastline.

*   **Seasonal Variations (B):** Seasonal changes in wind patterns, temperature, and precipitation significantly impact oceanic currents. For instance, monsoon winds in the Indian Ocean reverse direction seasonally, leading to a corresponding reversal in the direction of surface currents. Changes in temperature affect water density, which drives thermohaline circulation (a deep ocean current system). Seasonal melting of ice also affects salinity and density, influencing current flow.

*   **Bottom Reliefs (D):** The topography of the ocean floor, including underwater mountains, ridges, and trenches, affects the flow of deep ocean currents. These features can deflect, channel, or even block currents, causing them to change direction or speed. Bottom relief is particularly important for deep-water currents, which are less influenced by wind.

**Why Other Options are Incorrect**

*   **Option 1: (A), (B), (C) and (D):** This option includes all the factors. While the Shape of Coastline (A), Seasonal Variations (B), and Bottom Reliefs (D) are all factors that modify oceanic currents, the Revolution of the Earth (C) is not a direct modifier. The Earth's rotation causes the Coriolis effect, which deflects currents, but the *revolution* itself (the Earth's orbit around the sun) does not directly modify currents. Seasonal variations (B) are a result of the Earth's revolution and tilt, but the revolution itself is not a direct modifier.

*   **Option 3: (A) and (B):** This option only includes the Shape of Coastline (A) and Seasonal Variations (B). While these are important factors, it omits Bottom Reliefs (D), which significantly influences deep ocean currents. Therefore, it's an incomplete answer.

*   **Option 4: (A), (B) and (C):** This option includes the Shape of Coastline (A), Seasonal Variations (B), and Revolution of the Earth (C). As explained above, the Revolution of the Earth (C) is not a direct modifier of oceanic currents. The Coriolis effect, caused by the Earth's *rotation*, is a modifier, but the revolution itself is not.