The block of wood and the iceberg it was attached to was found 66 degrees south and just a tad north of Commonwealth Bay. It was spotted by wildlife watchers near Aurora Australis’ bridge. It was first assumed as a seal resting on the iceberg, but then they realized that it was a rectangular piece.
Compasses work just fine there as earths magnetic field is not limited to the actual planet.
The block is resting on level surface without any sinking into the ice below, so it has not been there for very long. It has never been "inside" the ice as the melt would have been uneven...
That piece of wood has most likely been put there by the photographer or someone is playing a trick on him/her. Sheesh.