World’s largest iceberg A23a on collision course with British island

The world’s largest and oldest iceberg is on a collision course with a British island in the South Atlantic, raising fears colonies of penguins and seals could be wiped out.

The mega-iceberg, known as A23a, is twice the size of Greater London and broke off the Filchner Ice Shelf in Antarctica in 1986, before running aground for 30 years.

It became dislodged from the seafloor in 2020 and began drifting northwards until it was trapped in a swirling ocean vortex last year, and then slingshotted in the direction of the island of South Georgia in January.

It is now only 280km away from the British overseas territory and is expected to make contact in two to four weeks, depending on the currents.

Iceberg A23a is heading towards South Georgia, raising fears for the British island's penguin and seal colonies. Photo / 123rf

“Icebergs are inherently dangerous. I would be extraordinarily happy if it just completely missed us,” sea captain Simon Wallace told the BBC, speaking from the South Georgia government vessel Pharos.

“We have searchlights on all night to try to see ice, it can come from nowhere.”

In the past, penguin chicks and seal pups in South Georgia have died after giant icebergs blocked access to their feeding grounds.

A23a’s vast cliffs tower higher than London’s Shard at 400m and cover 3500sq km, roughly the size of Cornwall, though the warmer northern waters are melting the iceberg and could break it up.

Should it disintegrate, the segments could float around South Georgia uncontrollably for years, putting the territory’s king penguins and elephant and fur seals in danger.

In 2004, an iceberg called A38 grounded on the continental shelf to the northeast of South Georgia, devastating the penguin and seal populations by preventing them from using their foraging routes.

“South Georgia sits in ‘iceberg alley’, so impacts are to be expected for both fisheries and wildlife, and both have a great capacity to adapt,” Mark Belchier, a marine ecologist who advises the South Georgia government, told the BBC.

A team with the British Antarctic Survey aboard the Sir David Attenborough research vessel investigated A23a in 2023, sailing into a crack and collecting water samples.

Andrew Meijers, chief scientist on the vessel, said: “It is amazing to see this huge berg in person – it stretches as far as the eye can see.”

Laura Taylor, a biogeochemist who also took part in the mission, said in December: “We know that these giant icebergs can provide nutrients to the waters they pass through, creating thriving ecosystems in otherwise less-productive areas.

“We took samples of ocean surface waters behind, immediately adjacent to and ahead of the iceberg’s route. They should help us determine what life could form around A23a.”

South Georgia has been under UK administration since 1908.

In March 1982, Argentine labourers occupied the island, taking prisoner 22 Royal Marines and British Antarctic Survey personnel working at a scientific station.

The move was a precursor to Argentine forces invading the British overseas territory of the Falkland Islands on April 2, 1982, and South Georgia the following day, sparking a 74-day war.