World's largest iceberg A23a is on the move, drifting away from Antarctica after decades grounded

New footage has been taken of the world's largest iceberg on its journey drifting beyond Antarctic waters, after it broke free from being grounded for more than three decades.

Scientists revealed last week that the Antarctic iceberg, called A23a, was on the move.

Since calving off West Antarctica's Filchner-Ronne Ice Shelf in 1986, the iceberg — which once hosted a Soviet research station — has largely been stranded after its base became stuck on the floor of the Weddell Sea.

But not anymore.

Recent satellite images reveal that the berg, weighing nearly a trillion metric tonnes, is now drifting quickly past the northern tip of the Antarctic Peninsula, aided by strong winds and currents.

At almost 4,000 square kilometres, A23a is roughly three times the size of New York City, slightly smaller than Kangaroo Island and a bit less than twice the size of the ACT.

It is rare to see an iceberg of this size on the move, British Antarctic Survey glaciologist Oliver Marsh said, so scientists will be watching its trajectory closely.

As it gains steam, the colossal berg will likely be launched into the Antarctic Circumpolar Current.

This will funnel it toward the Southern Ocean on a path known as "iceberg alley", where others of its kind can be found bobbing in dark waters.

Why the berg is making a run for it now remains to be seen.

"Over time, it's probably just thinned slightly and got that little bit of extra buoyancy that's allowed it to lift off the ocean floor and get pushed by ocean currents," Dr Marsh said.

Research team documents encounter with 'mega iceberg'

Scientists aboard the RRS Sir David Attenborough crossed paths with the "mega iceberg" while on a scientific mission heading towards the Weddell Sea.

The team documented their "lucky" encounter, releasing footage on Monday showing the enormous iceberg, which is around 400m tall above the water, stretching out into the distance beyond the research vessel.

"It is incredibly lucky that the iceberg's route out of the Weddell Sea sat directly across our planned path, and that we had the right team aboard to take advantage of this opportunity," Dr Andrew Meijers, chief scientist aboard the RRS Sir David Attenborough and Polar Oceans Science Leader at British Antarctic Survey (BAS), said in a statement.

The team collected samples of seawater around the iceberg, which Laura Taylor, a biogeochemist working on the vessel, said would help determine what life could form around A23a.

"Giant icebergs can provide nutrients to the waters they pass through, creating thriving ecosystems in otherwise less productive areas," she said.

"What we don’t know is what difference particular icebergs, their scale, and their origins can make to that process."

A23a is also among the world's oldest icebergs.

It is possible A23a could again become grounded at South Georgia Island. That would pose a problem for Antarctica's wildlife.

Millions of seals, penguins and seabirds breed on the island and forage in the surrounding waters, and the behemoth A23a could cut off such access.

In 2020, another giant iceberg, A68, stirred fears that it would collide with South Georgia, crushing marine life on the sea floor and cutting off food access.

Such a catastrophe was ultimately averted when the iceberg broke up into smaller chunks — a possible endgame for A23a as well.

But "an iceberg of this scale has the potential to survive for quite a long time in the Southern Ocean, even though it's much warmer, and it could make its way farther north up toward South Africa where it can disrupt shipping," Dr Marsh said.

By Reuters/ABC

Original article link: https://www.abc.net.au/news/2023-12-05/worlds-largest-iceberg-on-move-antarctica-/103188412