Which of the following is a cause of ocean currents?

• A. Wind
• B. Moon's gravity
• C. Erosion
• D. Volcanic activity

Answer: (A)

Surface ocean currents are driven primarily by wind. When the wind blows over the sea, friction drags the water along, and the movement is curved by the Earth's rotation (the Coriolis effect), creating large-scale patterns known as gyres. This wind-driven movement also drives processes like upwelling, where deep water rises to the surface and fuels nutrient-rich zones. The Moon’s gravity mainly causes tides—rises and falls in water level—not the steady horizontal currents that move across the ocean. Erosion and volcanic activity can affect coastlines or local water properties, but they don’t create the sustained, basin-wide horizontal currents that winds generate.