Britannica
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Why does cold salty water sink in polar regions?
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ocean current
Major ocean current systems of the world.
In polar regions, cold, salty water sinks because it reaches a high density that makes it heavier than the surrounding water. This process is driven by two primary factors:12
- Intense Cooling: Atmospheric cooling at high latitudes significantly lowers the water temperature. Because the density of seawater increases as its temperature decreases, this cooling makes the surface water increasingly dense.314
- Brine Rejection: As sea ice forms, salt is largely excluded from the ice structure. This process, known as brine rejection, increases the salinity of the remaining liquid water beneath the ice.15
The combination of low temperature and elevated salinity creates very dense water—such as Antarctic Bottom Water—which sinks to the deepest parts of the ocean. This sinking motion is a fundamental driver of thermohaline circulation, the global system of deep-ocean currents that continually replaces deep water with surface water.1324