Salt water freezes at a lower temperature than freshwater.
Seawater's freezing point decreases about 0.5 degrees Fahrenheit for each five parts per thousand increase in salinity. At 35 ppt sea water will begin to freeze at 28.6 degrees Fahrenheit. Typical dives lasted an hour with some shallow-depth dives stretching to ninety minutes underwater. Cold hands can be a limiting factor for many divers scuba diving under the Antarctic ice. Divers may not be cold right away, but given time and even the best diving gear, the cold seawater will triumph.