What primarily drives the circulation of subsurface ocean currents?

The circulation of subsurface ocean currents is primarily driven by the densities of ocean water, which are influenced by temperature and salinity. This phenomenon is known as thermohaline circulation. When water temperature decreases or salinity increases, the density of water increases, causing it to sink. In contrast, warmer or less saline water is less dense and stays near the surface. This difference in density creates a gradient that causes water to move, resulting in currents.

The interplay between these varying densities and the resulting movement of water is a crucial mechanism for distributing heat around the planet and plays a vital role in global climate patterns. While geographical features of the ocean floor, Earth's rotation, and wind patterns do affect ocean currents, they primarily influence surface currents or have secondary effects on subsurface circulation. The driving force for the deeper currents is fundamentally linked to the variation in water density.