| MadSci Network: Physics |
The freezing point depends on impurities in the water (suah as salt) and the pressure of the water....which is determined by a multitude of factors. In addition the top layer of ice insulates the lower layers from the cold atmospheric temperatures. As you get deeper in the water, the temperature of the water increases.
[Administrator's Note: In other words, it's complicated! If you need further details you should consult a thermodynamics textbook or a book dealing with differential equations.]
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