The world’s largest iceberg appears to have run aground off the coast of a remote British island home to millions of penguins and seals — potentially threatening local wildlife, but also providing an opportunity for research into such rare “megabergs.” 

Known as A23a, the massive slab of ice — roughly the size of Rhode Island and weighing nearly a trillion tonnes — was first reported to be heading toward South Georgia months ago, sparking concerns that it could collide with the island and disrupt the balance for local wildlife.

The British Antarctic Survey (BAS) said Tuesday that the iceberg had apparently struck the continental shelf that surrounds South Georgia, getting stuck roughly 73 kilometres from the island itself. 

Whether A23a will be stuck for an extended period — and what impact it could have on local wildlife — is still up in the air. 

“It will be interesting to see what will happen now,” Andrew Meijers, an oceanographer with BAS, said Tuesday. 

The sub-Antarctic island of South Georgia is a British overseas territory that lies north of Antarctica and some 1,850 kilometres east of South America. It supports a tiny, non-permanent population of scientists and researchers, but is known best for its abundance of wildlife, including five million seals across four different species and 65 million birds across 30 different species. Among them are the wandering albatross, the largest flying bird in the world, and several types of penguins.

One of the concerns among researchers is that the iceberg could block wildlife from their normal pathways to feeding sites, forcing them to travel longer distances and bring back less food to their young. 

But Meijers noted that icebergs store important micronutrients which are released when they melt, and can also stir up nutrients settled in deep water, potentially benefiting the local ecosystem. 

If this “towering wall” of ice stimulates ocean productivity, it could “boost populations of local predators like seals and penguins,” he said.  

40-year journey 

Running aground is the latest development in the dramatic, 40-year life of this ice giant. 

A23a broke off from Antarctica’s Filchner Ice Shelf in 1986, but remained stuck on the seabed in the Weddell Sea for the next three decades.

After breaking free in 2020 and riding ocean currents north past the tip of the Antarctic Peninsula, A23a hit another snag: an oceanic vortex called a Taylor Column, which trapped it spinning in place for months on end. 

Since wriggling out of the vortex, A23a has been slowly spiralling toward South Georgia. 

The government of South Georgia and the South Sandwich Islands said in a statement in January that it was “closely monitoring” A23a’s progress, and that while shipping and fishing could be affected, “impacts on wildlife are likely to be localised and transient.”

Satellite imagery showed the iceberg approaching the continental shelf in late February, before it appeared to freeze in place as it ran aground, with no major movement visible since March 1.

What could happen

Donavan Tremblay, an ice specialist with Canada’s Coast Guard, told CBC News that it was “very possible” A23a could start moving again as it’s more exposed to storms near the island that could shake or break it. 

But “it could also stay there for a while,” he said. 

Although icebergs of this size are relatively rare, this isn’t the first time a megaberg has threatened South Georgia. In 2020, an iceberg called A68a — previously world’s largest, and the sixth largest recorded iceberg of all time — split apart near the island after impacting the shelf.

A 2022 study found that A68a released 152 gigatonnes of fresh water and nutrients into the ocean near South Georgia. This changed the salt concentration of the surface water enough for the effect to persist for more than two months after the iceberg’s melt, according to a separate 2023 study.

Scientists are still digging into the impact that this had on the local ecosystem — including on whales, seals and plankton levels — and A23a is helping.

One focus Meijers highlighted is how the release of nutrients might help generate blooms of phytoplankton, and potentially increase the ocean’s ability to capture more carbon dioxide from the atmosphere.  

Other scientists want to know what happened underneath A23a, which would have gouged huge scars into the seabed and potentially triggered underwater landslides, says Alex Normandeau, a research scientist with the Geological Survey of Canada. 

“What are the consequences on the marine geology?” he asked. “Because it affects the habitats that are there, where the iceberg is grounded, but it also affects sedimentary suspension and underwater processes.”

Icebergs splitting off from Antarctic ice sheets and drifting north is a regular part of the life cycle of ice in the Antarctic, but Meijers says data has shown that ice shelves have been losing more mass over the past 20 years — a development scientists attribute to climate change. 

“These are pressing and active areas of research at BAS and elsewhere,” he said.