Figure this one out.
I thought air was less dense than water.
Iceberg the size of Manhattan from NASA's Earth Observatory
In early November 2013, a large iceberg separated from the front of Antarctica’s Pine Island Glacier. It thus began a journey across Pine Island Bay, a basin of the Amundsen Sea. The ice island, named B31, will likely be swept up soon in the swift currents of the Southern Ocean, though it will be hard to track visually for the next six months as Antarctica heads into winter darkness.
http://earthobservatory.nasa.gov/IOTD/view.php?id=83519
Water Balloons in space