Which process describes the sinking of denser water in the ocean?

The process that best describes the sinking of denser water in the ocean is downwelling. Downwelling occurs when surface water, which is often heavier due to factors such as increased salinity or reduced temperature, becomes denser than the water below it and sinks. This process is essential in maintaining the circulation of ocean currents and plays a significant role in redistributing heat and nutrients throughout the ocean.

In coastal regions where water may become denser due to evaporation or cooling, downwelling can help transport oxygen-rich water to deeper depths, supporting marine life in those areas. The dynamics of downwelling are crucial for understanding how oceanic and atmospheric conditions interact, influencing global climate patterns.

The other processes mentioned involve different mechanisms: upwelling refers to the rising of nutrient-rich water from deeper in the ocean to the surface, thermohaline circulation describes the large-scale movement of water due to differences in temperature and salinity across the globe, and surface runoff is related to freshwater flowing into the oceans from land, which does not directly describe the sinking of water.