The iceberg known as A23a was twice the size as Greater London and 400m thick, weighing almost one trillion tons. It is known as the biggest iceberg in the world.

The name A23a itself comes from the quadrant the iceberg was first spotted in A – 0-90W (Weddell sea) and the number 23 means that it is the 23rd iceberg spotted in that quadrant, icebergs discovered these days in sector A are numbered in the 80s.

“It stretches as far as the eye can see,” noted the chief scientist on board and Polar Oceans Science Leader at BAS, Dr Andrew Meijers.

A23a, once a part of an ice shelf, broke away in 1986 and since then it has largely been estranged as it stuck to the floor of the Weddell sea. But now it is continually on the move, after first being spotted slowly becoming mobile in 2020.

This movement has in recent months become ‘rapid’. In late 2023 the iceberg broke headlines when it exited Antarctic waters for the Southern Ocean. Here, it has followed a path referred to as the “iceberg alley” where many others of the same kind can be found.

Already huge arches and caves have already been eroded away in what the BBC describes the “final months of its existence.”

Currently the RRS Sir David Attenborough team’s research mission, as part of the British Antarctic Survey (BAS), is to see how sea ice and Antarctic ecosystems drive global ocean carbon and nutrient cycles.

Dr Meijers remarked how it is “incredibly lucky” that the iceberg was on their route and so they were able to collect valuable samples.

The results from their ongoing research will aid understanding of how climate change is affecting the Southern Ocean and the organisms that live there, and their roles in regulating the climate and keeping the oceans healthy.

Speaking with Reuters, British Atlantic Survey glaciologist Oliver Marsh said: “It’s rare to see an iceberg of this size on the move.” As this particular iceberg’s base has been stuck to the floor of the Weddell sea, scientists are unsure what caused the move. But Marsh has suggested that the iceberg has “thinned slightly” giving it the buoyancy to lift off the ocean floor.

You can read more about the climate science mission research here