What is defined as the movement of water from the surface to greater depths?

The movement of water from the surface to greater depths is best described as downwelling. This process occurs when surface water becomes denser than the water beneath it, often due to increases in salinity or decreases in temperature. As a result, this denser water sinks, transporting oxygen and nutrients from the surface to deeper ocean layers, which is crucial for maintaining ocean health and supporting marine life. Downwelling plays an essential role in the global ocean circulation system, helping regulate climate and distribute heat across the planet.

In contrast, upwelling refers to the movement of deeper, colder, and often nutrient-rich water rising to the surface, which is important for boosting productivity in certain areas. Thermohaline circulation involves large-scale ocean currents driven by temperature and salinity variations but is not specifically about water moving downward. Surface runoff describes water that flows over land and ultimately returns to bodies of water rather than moving into the ocean depths.