Brine rejection occurs in the sea ice packs around at the north and south poles of the Earth. The Arctic Ocean has historically ranged from roughly 14-16 million square kilometers in late winter to roughly 7 million km each September. The annual increase of ice plays a major role in the movement of ocean circulation and deep water formation. The density of the water below the newly-formed ice increases due to brine rejection. Saltier water can also become colder without freezing.
The dense water that forms in the Arctic are called North Atlantic Deep Water (NADW), while the Antarctic Bottom Water (AABW) forms in the southern hemisphere. These two areas of brine rejection play an important role in the thermohaline circulation of all of Earth's oceans.