How would they prove that?
There is no question that ice floats (wt argument that this unusual property of water gives us liquid water, because it kept the oceans from freezing from the bottom up.} water gets less dense as its temperature falls, not rises.
Antartica would have floated 4000 years ago, the rising tide lifts all bodies. even the atmosphere.
we know the deluge date. No anomalies from a global catastrophe in the cores corresponding to that era detected. Imagine 9000 meters of water falling as snow on top of the ice, in 40 days, the mark that would make. The change in radiation levels from losing that water canopy shield.
good thing the titanic Ark did not hit a floating iceberg the size of Antartica.