The largest iceberg in the world — A23a, nearly 1,500 square miles, about three times as big as New York City — has broken free of its anchor on the floor of the Weddell Sea and begun to drift toward the Southern Ocean.
By Cristen Hemingway Jaynes
In 1986, the Antarctic iceberg calved off the Filchner-Ronne Ice Shelf in the western part of the continent, quickly becoming stuck on the seafloor, reported Reuters.
According to Dr. Andrew Fleming, a British Antarctic Survey (BAS) remote sensing expert, it was only a matter of time before the colossal chunk of ice broke loose.
“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 said, as the BBC reported. “It was grounded since 1986 but eventually it was going to decrease (in size) sufficiently to lose grip and start moving. I spotted the first movement back in 2020.”
At the time of its calving, A23a was home to a Soviet research station.
The iceberg, which weighs about a trillion tons and is also one of the planet’s oldest, has recently begun moving more quickly with the aid of currents and winds and is drifting past the Antarctic Peninsula’s northern tip.
Oliver Marsh, a glaciologist with BAS, said seeing such a giant iceberg actually moving is a rarity, reported Reuters.
“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,” Marsh said, as Reuters reported.
The huge berg will most likely become swept up by the Antarctic Circumpolar Current, which will push it in the direction of the Southern Ocean and “iceberg alley,” where other icebergs float.
In 1916, the Anglo-Irish explorer Ernest Shackleton used the current in his harrowing Antarctic escape after his ship Endurance became trapped, broke up and sank in the Weddell Sea the previous year, reported CBS News. The sunken shipwreck was discovered in 2022.
Another possible outcome for A23a is for it to run aground at South Georgia Island, which would threaten the millions of penguins, seabirds and seals that breed on the Antarctic island and follow established foraging routes in its surrounding waters.
A separate iceberg, A68, looked as though it might crash into South Georgia Island in 2020, but ended up breaking apart, which could also happen to A23a.
However, Marsh explained, “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,” as Reuters reported.
However, these enormous shards of ice are not just dangerous beauties floating through remote, chilly waters. They serve an important purpose in the larger ecosystem by releasing minerals as they melt, reported the BBC. The dust that collected in their ice as they scraped along Antarctica’s rock bed serves as a nutrient source for tiny organisms at the base of marine food chains.
“In many ways these icebergs are life-giving; they are the origin point for a lot of biological activity,” said Dr. Catherine Walker, a scientist with the Woods Hole Oceanographic Institution, as the BBC reported.