40-year-old 'mega' iceberg — the largest on Earth — is on the move after being trapped in a giant vortex for months

The world's largest iceberg is on the move again after escaping from a giant vortex that caused it to spin in place for months. This is the big berg's second great escape in as many years, after breaking free from the seafloor where it was stuck for 37 years in 2023.

Scientists are now closely monitoring the icy slab's slow march toward oblivion in hopes of learning more about the temporary hidden ecosystem it may support.

A23a, which is often dubbed a "megaberg," has a surface area roughly three times larger than New York City and weighs just under 1 trillion tons. It first broke off from Antarctica's Filchner Ice Shelf in 1986 but became trapped on the seafloor just a few miles offshore, which has significantly slowed its melt rate. Over the last few decades, it has held the title of "world's largest iceberg" on multiple occasions, most recently since May 2023, when the previous largest berg — A-76A — broke apart.

Late last year, A23a finally broke free from its seafloor tether and began moving away from Antarctica. But it didn't get far. Just a few months later, the enormous ice island got trapped to the east of the South Orkney Islands in a Taylor column — a giant mass of rotating water caused by ocean currents circling an underwater mountain, or seamount. At its maximum spin speed, the berg was rotating about 15 degrees counterclockwise every day, researchers wrote on YouTube.

But as of Dec. 13, the megaberg has escaped from the Taylor column and resumed its journey away from the South Pole, according to a statement by the British Antarctic Survey (BAS).

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"It's exciting to see A23a on the move again after periods of being stuck," Andrew Meijers, an oceanographer at BAS, said in the statement. "We are interested to see if it will take the same route the other large icebergs that have calved off Antarctica have taken. And more importantly what impact this will have on the local ecosystem."

Drake Passage, the 'iceberg graveyard'

Most massive icebergs that break off from Antarctica drift north through a section of the Southern Ocean known as the Drake Passage, which has become known as the "iceberg graveyard" because it propels icebergs north into warmer waters, where they eventually break apart.

This is what happened to A-76A last year and its predecessor A68a, which also passed through this region before being ripped in half by ocean currents in 2020.

Researchers are keeping a particularly close eye on A23a to learn more about how its eventual breakup may impact the surrounding ocean ecosystem.

"We know that these giant icebergs can provide nutrients to the waters they pass through, creating thriving ecosystems in otherwise less productive areas," Laura Taylor, a doctoral candidate in biogeochemistry with BAS, said in the statement. "What we don't know is what difference particular icebergs, their scale, and their origins can make to that process."

Scientists have taken water samples throughout the iceberg's predicted path and will continue to take samples in its wake. Comparing these samples with one another should help shed light on this mystery.