How cold is the water at the North Pole?
Temperature Both air and sea temperature are vital for the freeze/melt processes. Ice will form if air temperature is lower than the freezing point of the water below. The greater the temperature gradient between air and sea is, the more efficient the heat transfer. If the difference between air and water is not large enough, heat conduction within the water column itself will keep the surface water from freezing. Salinity Surface salinity is also of importance. Freshwater freezes more easily than salt water – zero salinity requires a temperature of zero degrees Celsius, whereas “normal” sea water with salinity around 34 psu (practical salinity units, comparable to parts per mille (thousand)) must be cooled down to almost -2 Degrees C. Areas with large amounts of excess melt-water from the previous season, or extensive freshwater input from rivers and precipitation are well disposed for ice production. In the central Polar Seas, a deep layer of freshwater also tends to isolate the sea
