• A23a, the world's largest iceberg, has run aground off South Georgia, in the South Atlantic.
• Located 80 kilometres from the coast, it will not block sea access for penguins and seals.
• As it moves into warmer waters, it has already lost mass and will continue to break apart.

It was the end of November 2023 when sources from the scientific community reported that the world's largest iceberg, known as A23a, was drifting away from Antarctica. More than a year on, its journey appears to have come to an end, at least for now. As the BBC reports, this enormous mass of ice has run aground off South Georgia, a near-uninhabited island in the South Atlantic Ocean, where it has begun to break apart. For now, then, it is far enough from the coast to pose no threat to penguins and seals. But there will be consequences nonetheless.

The journey of the world's largest iceberg

The calving of A23a from the Filchner-Ronne ice shelf in West Antarctica dates back to 1986. At the time, however, the iceberg remained close to the coast, anchored on the seabed of the Weddell Sea. In November 2023, satellite imagery revealed it had begun moving again, driven by currents and strong winds. At the time it measured nearly 4,000 square kilometres (slightly smaller than the Italian region of Molise) and was approximately 400 metres thick.

Since then, as it has drifted into warmer seas, it has progressively shrunk. It is now estimated to cover just over 3,200 square kilometres and to be 300 metres thick: it is no longer a large pristine block, as caverns are visible along its edges. On Saturday 1 March, A23a struck the continental shelf roughly 80 kilometres from the coast of South Georgia and appears to have come to a halt there. Had it drifted closer, it would likely have blocked sea access for penguins and seals — an eventuality that does not appear to be materialising for now.

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🧊 Scientists have said that the colossal #A23a #iceberg – which is more than twice the size of Greater London – has run aground 73km from an important haven and breeding ground for penguins and seals in the Antarctic.

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What to expect from the melting of A23a

"All icebergs are destined to disappear", Professor Huw Griffiths, a crew member aboard David Attenborough's polar research vessel, which is currently in Antarctica, told the BBC. "It is quite remarkable to see that A23a has lasted this long having only lost a quarter of its surface area."

If — as is widely expected — it continues to break apart, there will be various consequences. Smaller icebergs, as they calve off, could obstruct shipping routes and fishing. Scientists also point out that the melting ice could release large quantities of nutrients into the ocean that have until now been trapped within it. When this happens, it will be possible to observe a green halo caused by phytoplankton blooms.

At the same time, the tides will continue to push this gigantic and enormously heavy sheet of ice, causing it to repeatedly strike the continental shelf. This will sweep away small creatures such as corals, sponges, and sea slugs. But this, experts explain, is a normal phase in the ecosystem's life cycle. The worst-case scenario — in which it drifts too close to the island — appears, for now, to have been averted.