Why do ice Bergs float?

H2O is lighter as a solid than a liquid.

When things freeze/cool they shrink (their particles become closer togoether)all, except ice.

When water freezes into ice it actually expands and the molecules form a lattice structure. This actually means its becomes less dense than water.

Sea water also contains many salts (ie the dead sea is incredibly salty and you float much easier than in "normal" sea water) and this makes it even more dense than fresh water (remember ice is pure fresh water).