Brine rejection that drains from the newly formed ice is replaced by a weak flow of relatively fresh water, from the liquid region below it. The new water partially freezes within the pores of the ice, increasing the solidity of the ice. As sea ice ages and thickens, the initial salinity of the ice decreases due to the rejection of brine over time [Fig. 2]. While the sea ice ages, desalinization occurs to such a degree that some multiyear ice has a salinity of less than 1 PSU. This occurs in three different ways: Brine rejection occurs in the sea ice packs
Properties of water the bottom of frozen-over fresh water lakes and rivers. As the surface of salt water begins to freeze (at −1.9 °C for normal salinity seawater, 3.5%) the ice that forms is essentially salt-free, with about the same density as freshwater ice. This ice floats on the surface, and the salt that is "frozen out" adds to the salinity and density of the sea water just below it, in a process known as "brine rejection". This denser salt water sinks by convection and the replacing seawater is subject to the same process. This produces essentially freshwater ice at −1.9 °C on