Explained: How is world's largest iceberg drifting away from Antarctica?

The world's largest iceberg is drifting, for the first time in over 30 years, as per the British Antarctic Survey. The recent satellite pictures showed that the Antarctic iceberg called A23a was moving beyond the northern tip of the Antarctic Peninsula, propelled by strong winds and currents.

British Antarctic Survey glaciologist Oliver Marsh said it was rare to see an iceberg this big moving and the scientists will be watching its course closely.

A remote sensing expert from the British Antarctic Survey Andrew Fleming told BBC that the iceberg was drifting apart for a year and it seemed to have picked up the pace now. “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.”

Here is all you need to know about A23a and why and how it is moving.

What is the A23a iceberg and what happened?

A23a iceberg is 400 meters thick and has about 4,000 square km area, which makes it thrice the size of New York City and two times the size of Great London. It weighs about a trillion metric tonnes.

Since it split from West Antarctica's Filchner-Ronne Ice Shelf in 1986, A23a has been stranded since its base got stuck at the bottom of the Weddell Sea.

The iceberg is likely to move towards the Southern Ocean. It has been on the move since 2020. Fleming said, “It was grounded since 1986 but eventually it was going to decrease (in size) sufficiently to lose grip and start moving. I spotted first movement back in 2020.”

British Antarctic Survey glaciologist Oliver Marsh told 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”

A23a once had a Soviet research station on it. Moscow sent out an expedition to retrieve equipment from the Druzhnaya 1 base, concerned about potential loss. However, the tabular iceberg remained relatively close to the coast, and its deep keel securely anchored it to the Weddell Sea's bottom muds, hindering movement.

Since the 1980s, A23a has held the “largest current iceberg” title, several times mostly being surpassed by larger but short-lived icebergs.

What next?

Like most icebergs, as it gains pace, A23a is likely to be launched into the Antarctic Circumpolar Current. It will then move towards the Southern Ocean, on a path known as “iceberg alley”, where several other icebergs can be seen floating in dark waters.

As it moves, A23a may once again risk grounding at South Georgia island, creating challenges for the region's wildlife. The island serves as a breeding ground and foraging area for millions of seals, penguins, and seabirds. The massive iceberg could potentially impede their access.

In 2020, a similar concern arose with iceberg A68, raising fears of a collision with South Georgia that could harm marine life and disrupt the food chain. Fortunately, A68 eventually fragmented into smaller pieces, offering a potential resolution for A23a as well.

Marsh told Reuters, “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 reported by CNN, as it would be carried by ocean currents, A23a is likely to move eastward and is currently travelling five kilometres a day.

British Antarctic Survey scientists Ella Gilbert and Marsh have said that while A23a broke off due to the natural growth cycle of an ice shelf, climate change has been driving stark changes in Antarctica’s ice and the continent was losing huge quantities of ice each year.

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