Seawater Freezes at About 28.4 Degrees Fahrenheit

The ocean can freeze, but it has to get colder than a pond does. NOAA’s National Ocean Service explains that fresh water freezes at 32 degrees Fahrenheit, while seawater freezes at about 28.4 degrees Fahrenheit because of the salt in it. The ice itself is not very salty. According to NOAA, when seawater freezes the ice contains very little salt, because only the water part freezes. Frozen ocean is far from rare. NOAA says at least 15 percent of the ocean is covered by sea ice for some part of the year. Salt changes how water behaves as it cools, too. Seawater becomes denser and denser right down to its freezing point, whereas fresh water is most dense at 39.2 degrees Fahrenheit, well above its freezing point.