Here's why:

* Freezing: When seawater freezes, the ice that forms is mostly pure water, leaving the salt behind in the unfrozen water. This process, called brine exclusion, makes the remaining seawater saltier.

* Melting: As polar ice caps and glaciers melt, they release fresh water into the ocean, diluting the surrounding seawater and lowering its salinity.

* Evaporation: While evaporation is a major factor in increasing salinity in warmer oceans, it's less significant in polar regions due to the cold temperatures.

So, while polar regions experience high salinity in specific areas due to brine exclusion, the overall salinity of polar water is lower than in other parts of the ocean.