At what temerature does salt water (the sea) freeze?

Answer 1

About 28.6 F = -1.9 C for seawater of typical salinity

http://en.wikipedia.org/wiki/Water_(molecule)#Density_of_saltwater_and_ice

Of course, as seawater freezes, the ice is salt-free, making the liquid water that is left higher in salt content, and so having a lower freezing point. The -1.9 C holds for the open ocean, where mixing and dilution in the vast volume keep the overall salt content nearly constant.

Answer 2

The freezing temperature of salt water depends on how much salt you put in. Oceanographers define the "salinity" of water as the number of grams of salt per 1000 grams of water. (Since 1000 grams of water is almost exactly 1 liter, it's also grams of salt per liter).

Here's a table which gives the freezing point of water at a number of different salinities:

S(g/kg) 0 10 20 24.7 30 35
T(freezing) (C) 0 -0.5 -1.08 -1.33 -1.63 -1.91

Answer 3

I think if you took a bucket of sea water and started cooling it, you would see the first ice crystals around 25deg F but it would take about 0 deg F to freeze the last bit of water.