What is the primary factor that drives ocean currents?

The primary factor that drives ocean currents is the combined effect of wind and the Earth's rotation. Winds are crucial as they blow across the surface of the ocean, transferring energy to the water and creating surface currents. These currents are then affected by the Coriolis effect, which is the result of the Earth's rotation. The Coriolis effect causes moving water to turn and swirl, influencing the direction of the currents.

While temperature differences and salinity of the water do play a significant role in the ocean's overall circulation patterns, they serve more to affect density and stratification, which can influence deep ocean currents rather than being the primary force driving the surface currents. Similarly, while the gravity of the Moon does cause tides, it is not a direct driving force for ocean currents but rather impacts water levels temporarily. Hence, the interaction between wind and the Earth's rotation is the fundamental mechanism that sets ocean currents in motion.