What phenomenon occurs when sea ice forms in the polar regions?

When sea ice forms in polar regions, the process of freezing excludes salt from the ice crystal structure, resulting in an increase in the salinity of the surrounding seawater. This occurs because as the seawater freezes and ice forms, pure water molecules are incorporated into the ice, while the salt remains in the liquid phase. Consequently, the salinity of the water just beneath the ice increases, as the dissolved salts are concentrated in a smaller volume of water.

This phenomenon is significant because the increase in salinity can impact the density of the seawater, affecting ocean circulation and the overall ecology of the polar marine environment. It contributes to the unique characteristics of polar water, including its stratification and its role in global thermohaline circulation.