Vessels heading south beware. An iceberg the size of Luxembourg has split away from the Antarctic ice shelf and is floating free in the Southern ocean.
It was created when another giant berg smashed into the Mertz glacier, itself cracked and weakened by global warming. A huge chunk broke off, and both are now side by side in normally ice-free water.
The biggest worry is not navigation. The bergs may prevent cold, dense, super-saline water from descending to the ocean floor at one of the only places in the world where this vital oxygenating process takes place.
It could also affect ocean currents around the world.