What drives thermohaline circulation in the oceans?

Thermohaline circulation is primarily driven by differences in water density, which are significantly influenced by temperature and salinity. This process is also known colloquially as the "ocean conveyor belt," as it describes the large-scale movement of ocean water that results from these density differences.

When water at the surface is heated by the sun, it becomes less dense and tends to stay near the surface. Conversely, cold water is denser, and when seawater freezes or evaporates, the remaining water becomes saltier and, thus, denser, causing it to sink. This sinking of cold, salty water in certain areas, particularly near the poles, creates a cascade effect, where the water that sinks pulls warmer water from other regions in a continuous loop through the world's oceans.

Understanding this mechanism is essential, as it plays a critical role in regulating Earth's climate by distributing heat around the planet. Wind patterns, seasonal weather changes, and even tectonic activity do affect ocean currents and surface conditions but do not drive thermohaline circulation as fundamentally as the interplay between temperature and salinity does.