The huge berg is now slowly spinning just north of the South Orkney Islands, a barren part of the British Antarctic Territory uninhabited except for an Antarctic exploration base.

The iceberg has stopped not because it has hit the seafloor, but because it is trapped in a vortex caused by the Pirie Bank, a bump on the ocean floor. As the current meets that obstruction, it separates into two flows, producing a rotating swirl of water in between.

“The ocean is full of surprises, and this dynamical feature is one of the cutest you’ll ever see,” Prof Mike Meredith from the British Antarctic Survey told BBC News.

A23a, which weighs nearly one trillion metric tons, could be stuck for years, scientists say.