A23a - the world’s largest and oldest iceberg - has run aground on the continental shelf near the island of South Georgia, scientists say.
The “megaberg” – which is twice the size of Greater London and has been compared to Game of Thrones’ ice wall – grounded about 56 miles (90km) from the British overseas territory in the South Atlantic on March 1, and hasn’t moved since.
The nearly one-trillion-tonne block of ice was calved from Antarctica’s Filchner ice shelf in 1986, and then remained grounded on the floor of the Weddell Sea for more than 30 years, the British Antarctic Survey (BAS) said.
Since 2020, it has been drifting with Southern Ocean currents towards South Georgia, which is home to elephant and fur seals, king penguins, and unique birds.
The warmer waters and the action of waves and tides are expected to break it up into smaller icebergs and eventually melt.
Fishing vessels could face “potentially hazardous” conditions from the smaller icebergs in the region, but scientists said nutrients stirred up from the grounding and melting of the megaberg could boost food for the region, including local penguins and seals.
The British Antarctic Survey said it has been closely watching the iceberg and tracking its progress since 2020, and particularly since 2023 when it moved out of the Weddell Sea into the wider South Atlantic.
For months late last year, the iceberg was trapped in a “Taylor column” which kept it spinning in one spot.
It is now grounded on the continental shelf with its nearest point some 45 miles (73km) from land, and has not moved since March 1, the BAS said.
Dr Andrew Meijers, an oceanographer at the British Antarctic Survey, said: “If the iceberg stays grounded, we don’t expect it to significantly affect the local wildlife of South Georgia.
“In the last few decades, the many icebergs that end up taking this route through the Southern Ocean soon break up, disperse and melt,” he said.
“Commercial fisheries have been disrupted in the past however, and as the berg breaks into smaller pieces, this might make fishing operations in the area both more difficult and potentially hazardous.”
A map of South Georgia and Sandwich Islands:
He said scientists are keen to see how the iceberg will affect the local ecosystem.
“Nutrients stirred up by the grounding and from its melt may boost food availability for the whole regional ecosystem, including for charismatic penguins and seals,” he said.
He said satellite tracking shows the iceberg appears to be maintaining its structure and has not yet broken up into smaller chunks as previous “megabergs” have done.
Icebergs of this size are “relatively rare”, Dr Meijers added, saying it had taken almost a whole day for the RRS Sir David Attenborough – the research vessel the public famously voted to call Boaty McBoatface – to sail along its length on a research trip in 2023.
“It looks like a towering wall emerging from the ocean, stretching from horizon to horizon,” he said.
While icebergs, including megabergs such as A23a, are a completely normal part of the lifecycle of the Antarctic ice sheets, human-driven climate change is causing melting and loss of mass of the ice shelves, he added.
