World’s biggest iceberg moving beyond Antarctic waters

One of the world’s largest icebergs is drifting beyond Antarctic waters, after being grounded for more than three decades, according to the British Antarctic Survey.

The iceberg, known as A23a, split from the Antarctic’s Filchner Ice Shelf in 1986. But it became stuck to the ocean floor and had remained for many years in the Weddell Sea.

Not any more. Recent satellite images reveal that the iceberg, weighing nearly a trillion metric tonnes, is now drifting quickly past the northern tip of the Antarctic Peninsula, aided by strong winds and currents.

The iceberg is about three times the size of New York City and more than twice the size of Greater London, measuring about 4,000 sq km (1,500 square miles).

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

As it gains steam, the colossal iceberg will probably 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. It is not clear why it is making a run for it now.

“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,” said Marsh. A23a is also among the world’s oldest icebergs.

Andrew Fleming, a remote sensing expert from the British Antarctic Survey, told the BBC on Friday that the iceberg had been drifting for the past year and now appeared to be picking up speed.

“I asked a couple of colleagues about this, wondering if there was any possible change in shelf water temperatures that might have provoked it, but the consensus is the time had just come,” Fleming told the BBC.

Fleming said he had first spotted movement from the iceberg in 2020. The British Antarctic Survey said it had now ungrounded and is moving along ocean currents to sub-Antarctic South Georgia.

It’s 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. 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 end game 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,” said Marsh.

With Reuters and Associated Press