Ice depth, ice caps and icebergs

Hello everybody, I have a few questions about the ice sea, can someone redirect me if I am in the wrong newsgroup ?

What are the maximum and average depth of the north pole ice cap ? The wikipedia gives it ~ 2 meters, but the groenland ice sea is said to be sometimes 1 kilometer thick. Where is the truth ?

Are there places where the air at -30° Celsius and the liquid water at 0° are separated by only a few meters of ice ? Wouldn't it be possible to extract energy for this temperature gradient, just as in the "Ocean thermal energy conversion" ? why not ?

Thanks

Yves
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