Why does ice float?
If I remember correctly, water is at it’s densest at about 39 or 40 degrees Farenheit. The surrounding water around the ice is about or near that temperature. Lowest specific gravity always floats, while highest sinks.
Same reason a boat floats: the ice has a greater volume than liquid water, so it's less dense than the same volume of water. An object that is less dense than the water it displaces is forced upward, i.e., is bouyant. Young engineers at Old Dominion University are given first-hand experience in this effect in their annual Concrete Canoe contest.