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Originally Posted by C4 Diesel
No, shake... While the thought of the water below the surface being under high pressure is a noble thought, that's not why it doesn't freeze first. The reason the top freezes first IS because it gets cold first. The cold comes from the air, which is above the water, and the resulting temperature profile would indicate that the water on the surface is the coldest, and would also therefore freeze first. The water on the top insulate the water on the bottom and it does not cool evenly.
Not to mention that 210 MPa is about 2,000 atm. Not even deepest parts of the oceans comes under that much pressure from water "weight". If I remember correctly, it takes 33ft of water to increase the pressure by one atmosphere, and one (or a few) atmosphere(s) will not significantly lower the freezing point of water.
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Actually the increase of pressure would allow for ice to freeze quicker. But that is a patsy answer since to increase pressure would lower the temperature on a closed environment. And you can treat the oceans for instance as a closed environment because of the depths involved. But again, the TOP FREEZES FIRST BECAUSE IT IS EXPOSED TO COLD AIR FIRST. Like any good chemistry student you should know that to increase the surface area where a reaction is taking place is to speed it up (like stirring!). Since the top of the pond is not stirring it freezes and then the ice as it gets colder forces the water beneath it to freeze in layers.