What drives thermohaline circulation?

• A. Density differences from temperature and salinity.
• B. Wind-driven surface currents.
• C. The Coriolis effect alone.
• D. Tidal forces only.

Answer: (A)

Density differences from temperature and salinity set the engine for thermohaline circulation. When surface waters cool or become saltier, their density increases and they sink, especially in polar regions. This sinking draws water from the surface into the deep ocean, and deeper waters must be replaced by upwelling elsewhere, creating a global loop that moves water between the surface and the depths. Winds and the Coriolis effect influence where and how currents flow, but they don’t provide the main energy that drives this large-scale pattern. Tidal forces contribute only minor mixing by comparison. So the primary driver is the density differences produced by temperature and salinity.