City-sized iceberg breaks away from Antarctica

The world’s largest iceberg is on the move.

The massive chunk of ice – known as A23a – is bigger in area than London and New York and even larger than the Australian Capital Territory. It’s now slowly moving northward into the Southern Ocean.

It’s been a long time coming.

A23a calved from the Filchner Ice Shelf in 1986, but remained grounded on the seafloor. It’s now migrating out of the Weddell Sea towards South Georgia and the South Sandwich Islands, nearly 2,000km east of South America’s southernmost point.

In total, A23a covers an area of about 3,900km² and extends about 400m deep.

Despite growing concerns about the behaviour of ice in Antarctica amid record global temperatures, the escape of A23a is not considered climate change related. Instead, its rapid movement north is the culmination of nearly four decades of build-up since it first broke away from its parent ice shelf.

It’s expected to follow other large icebergs that have split from Antarctic ice shelves and floated north.

“From the northern tip of the Antarctic Peninsula, where it is now, we expect it to take roughly the same path as the other large icebergs that have exited the Weddell Sea recently – most prominent examples are A68a and offspring and A76a and offspring,” says Dr Jan Lieser, a marine glaciologist at the University of Tasmania’s Institute for Marine and Antarctic Studies.

“That path will take it north-eastward towards South Georgia and if it survives that far – which is likely – even further.”

Scientists like Lieser can track the iceberg’s path using sophisticated satellite imaging and radar data – a practice known as remote sensing.

While A23a’s future will be an unfolding event, the journeys of A68a and A76a provide a template from which glaciologists can work.

As icebergs enter warmer waters, they will begin to disintegrate and it’s important that these processes are monitored – island-sized icebergs have the potential to wreak havoc with humans and the environment.

“When they break apart they create thousands of smaller icebergs and each and every one of them is a hazard for ships,” Lieser says.

“They may also ground around islands and block access to the coast not only for ships and humans, but also for animals that may want to rest on the shores of those islands.”

It’s not all bad news for nature though. Within the ice are snap-frozen nutrients, which will be injected back into the cold Southern Ocean waters as the berg continues its journey north. This benefits these complex ecosystems and tiny plankton and other organisms living within them.

“This could be viewed as a natural ‘ocean fertilisation process’,” says Lieser.

“When these icebergs melt, those nutrients are then released again and fertilise the water column, which in turn can support microorganisms to flourish which will then feed higher order predators again.”