World's largest iceberg runs aground in South Georgia and blocks off key penguin feeding ground

After nearly 40 years at sea, the world's largest iceberg has run aground on the remote British overseas territory of South Georgia, one of the biologically rich habitats on Earth home to millions of penguins, seals and endangered albatross.

The vast "megaberg" named A23a covers 1,200 square miles - roughly the size of Gloucestershire.

Now it has grounded it is expected to break up, threatening to prevent penguins and other sea-life from accessing crucial feeding grounds and the fishing vessels operating in the area.

Last week as it approached South Georgia it was moving "very fast," according to Dr Andrew Meijers, an oceanographer at the British Antarctic Survey in Cambridge.

"It was covering 30km a day, fairly ripping along for an iceberg," he said. Then on Friday it suddenly stopped, its corner snagging the seafloor about 40 miles off the southwest coast of South Georgia.

The stress of the collision, tides and currents are likely to speed the breakup of the 'berg in the warmer waters - 1,200 miles from Antarctica where it began its long, slow journey.

A23a broke off from Antarctica's Filchner-Ronne ice shelf in 1986, carrying a Soviet research station Druzhnaya built on it into the Wedell Sea.

The 'berg barely moved for 20 years, then in 2020 began drifting slowly north. It spent six months last year spinning in a revolving ocean current in the Southern Ocean before finally breaking free in the New Year on a collision course with South Georgia.

Apart from a handful of visiting scientists and officials representing the Falkland Islands-based government of South Georgia, the island is uninhabited - by people at least.

"This area is extremely important for penguins," said Peter Fretwell, a geospatial information scientist also at the British Antarctic Survey.

Several million penguins including macaroni, chinstrap, gentoo and king penguins call South Georgia home. As do several species of albatross, elephant seals and fur seals. The ocean around the islands is also increasingly important for whales, now returning after hunting them was banned.

The iceberg is blocking a vast area of ocean that is an important feeding ground for macaroni penguins - South Georgia is home to one of the world's largest colonies.

As it melts, A23a will be releasing millions of gallons of fresh water into the ocean each day.

Because fresh water floats on top of heavier seawater, it has the potential to force nutrients - and therefore the shrimp-like krill penguins feed on - deeper into the water column.

"If it's very clean water, it will introduce a halo of low-productivity around the iceberg," said Mr Fretwell.

However, the opposite could also happen. Some icebergs carry a lot of sediment with them, scraped from the rocks of Antarctica. Once released into the ocean this sediment can add nutrients to the water - potentially boosting the amount of food available for penguins.

Megabergs of this size are rare, too few for scientists to know if they're becoming more common or not.

However, they're emblematic of a clear warming trend in the Antarctic that is causing the increasingly rapid melting of its ice sheets, which are the world's largest.

The continent is losing around 150 billion tonnes of water in the form of ice a year, half carried away as icebergs, the rest due to ice melting directly off the continent itself.

A key concern is whether all that fresh water will disrupt what is effectively our planet's cooling system.

The Antarctic Circumpolar Current - a conveyor belt of cold water running around Antarctica - is the single most important system that removes rising levels of heat from our atmosphere.

Warm air from the rest of the planet heats the surface waters, and currents then draw this warmer water down, replacing it with cooler water from the depths of the ocean.

"It does all of the heavy lifting in terms of trapping heat from global warming," said Dr Meijers.

Microscopic plants - phytoplankton - in the region also absorb the most planet-warming carbon dioxide, which is, like the warmer water, carried deep into the oceans and stored there.

A recent study suggests fresh water from melting icebergs and the Antarctic continent is already slowing this circumpolar current and may reduce its speed by 20% by 2050.

A potentially worrying "positive feedback" that could further exacerbate global warming.

(c) Sky News 2025: World's largest iceberg runs aground in South Georgia and blocks off key penguin feeding ground