A23a: A giant iceberg on a collision course with an island

The world's largest iceberg has crashed into a remote British island, potentially putting penguins and seals at risk.

The iceberg is rolling north from Antarctica towards South Georgia, a rocky British territory and wildlife refuge, where it can break up and break into pieces. It is currently 173 miles (280 km) away.

Countless birds and seals died in South Georgia's icy bays and beaches when past giant icebergs prevented them from feeding.

“Icebergs are inherently dangerous. I would be extremely happy if they just let us through,” sea captain Simon Wallace told BBC News, speaking from the South Georgia government ship Pharos.

Around the world, a group of scientists, sailors and fishermen are eagerly checking satellite images to monitor the daily movements of this iceberg queen.

That's right known as A23a and is one of the oldest in the world.

It detached, or broke away, from the Filchner Ice Shelf in Antarctica in 1986, but became stuck on the sea floor and then became trapped in an ocean eddy.

Finally, in December, he broke free and is now on his final journey, speeding toward oblivion.

Warmer waters north of Antarctica are melting and weakening its massive cliffs, which rise to 1,312 feet (400 m), taller than the Shard in London.

It once measured 3,900 sq. km, but recent satellite images show that it is slowly disintegrating. Now it is about 3500 sq. km, roughly the size of the English county of Cornwall.

And great sheets of ice break off, plunging into the waters around its edges.

The A23a can break up into huge segments any day, which then hang around for years, like floating cities of ice, cruising uncontrollably around South Georgia.

This is not the first huge iceberg to threaten South Georgia and the Sandwich Islands.

In 2004 one, called A38, fell onto its continental shelf, leaving baby penguins and seal pups dead on beaches as massive chunks of ice blocked their access to feeding grounds.

The territory is home to valuable colonies of king penguins and millions of elephants and seals.

“South Georgia is in the alley of the iceberg, so impacts to both fisheries and wildlife, both of which have a large capacity to adapt, should be expected,” said Mark Belchier, a marine ecologist who advises the South Georgia government .

Sailors and fishermen say icebergs are a growing problem. In 2023 one called A76 spooked them when it came close to grounding.

“Pieces of it were tilting up so they looked like big ice towers, an ice city on the horizon,” said Mr Belchier, who saw the iceberg while at sea.

These plates still linger around the islands today.

“It's in pieces from the size of several Wembley stadiums to pieces the size of your desk,” says Andrew Newman of Argos Froyanes, a fishing company that operates in South Georgia.

“These pieces basically cover the island – we have to work our way through it,” says Captain Wallace.

The sailors on his ship must be constantly alert. “We have floodlights on all night to try to see ice – it can come out of nowhere,” he explains.

According to Mr Newman, the A76 was a “game changer” with a “huge impact on our operations and on keeping our ship and crew safe”.

All three men described a rapidly changing environment, with visible glacier retreat from year to year and unstable sea ice levels.

Climate change is unlikely to be behind the birth of A23a, since it was born so long ago, before much of the impact of the rising temperatures we see now.

But giant icebergs are part of our future. As Antarctica becomes more unstable with warmer ocean and air temperatures, larger chunks of the ice sheets will break off.

Before his time was up, however, A23a left a parting gift for scientists.

A team from the British Antarctic Survey on the research vessel Sir David Attenborough found themselves near A23a in 2023.

Scientists have scrambled to seize the rare opportunity to study what mega icebergs do to the environment.

The ship entered a crevasse in the iceberg's giant walls, and PhD student Laura Taylor collected valuable water samples 400 meters from its cliffs.

“I saw a massive wall of ice much higher than me as far as I could see. It has different colors in different places. Pieces were falling out – it was quite magnificent,” she explains from her laboratory in Cambridge, where she is now analyzing the samples.

Her work examines how meltwater affects the carbon cycle in the Southern Ocean.

“This is not just water that we drink. It's full of nutrients and chemicals, as well as small animals like phytoplankton frozen inside,” says Ms Taylor.

As it melts, the iceberg releases these elements into the water, changing the physics and chemistry of the ocean.

This can store more carbon deep in the ocean as particles sink from the surface. This would naturally block some of the planet's carbon dioxide emissions that contribute to climate change.

Icebergs are notoriously unpredictable, and no one knows exactly what they will do next.

But soon the giant must appear, looming over the horizons of the islands, as large as the territory itself.