Why does cooler water tend to sink in a convection current?

Cooler water sinks in a convection current primarily because it is denser than warmer water. When water cools, its molecules lose kinetic energy and move closer together, which increases the density of the water. In a convection current, this denser, cooler water will sink, while the warmer, less dense water rises. This process is fundamental to understanding convection in fluids, as it drives the circulation pattern: cooler water at the surface sinks to the bottom, and warmer water rises to take its place.

The other factors presented do not accurately explain why cooler water sinks. Although lower energy and lower heat capacity can contribute to temperature differences in water, the key driver for the sinking of cooler water is its increased density compared to that of warmer water.