A23a, a giant iceberg adrift | Polarjournal
Its surface area could contain three times New York City. The A23a iceberg recently began drifting north of the peninsula. Image: Copernicus-Sentinel-1

After more than 30 years of immobility, the A23a iceberg is back on track. Driven by winds and currents, it drifts in the Southern Ocean, with two possible trajectories: one towards South Georgia, the other towards South Africa, with possible disruption of shipping lanes for both animals and ships in both cases.

Since November 25, iceberg A23a, one of the world’s largest icebergs, has been on the move again.

Formed in 1986 when it calved from the Filchner-Ronne ice shelf in the north-western part of the continent, the iceberg eventually ran aground in the Weddell Sea, where it remained still until 2020. Movements were noted at the time. Then, on November 25, the Copernicus-Sentinel-1 satellite showed it drifting north of the peninsula.

Produced by the British Antarctic Survey, this timelapse uses Copernicus-Sentinel-1 satellite images of the A23a iceberg drift. Video : New Scientist / YouTube

With a 3 900 square kilometers area and a 400 meters thickness, this ice giant weighs a billion tons. Driven by strong winds and currents, the iceberg moves at a speed of five kilometers a day. It should follow the currents towards the Southern Ocean by following the iceberg alley, a trajectory taken by numerous icebergs drifting from Antarctica.

The reason for this sudden drift after 37 years of immobility can certainly be explained by the iceberg’s loss of mass. “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”, told recently Dr. Andrew Fleming of the British Antarctic Survey to the BBC. Nailed to the bottom of the Weddell Sea since 1986, the iceberg has probably melted, diminishing in size and losing its grip on the sea floor.

The A23a iceberg started moving again in 2020. Here we see the mastodon’s progress between June 30, 2020 (in red) and August 31, 2020 (in blue). Image: Copernicus-Sentinel-1 / Polar View

When it was still attached to the Filchner-Ronne ice barrier, the A23a was home to a research station, Druzhnaya I. Built in 1975, this Sovietic scientific base was evacuated in 1987 when the iceberg began to calve from the ice shelf. Relocated near Cape Norvegia, on the northeast coast of the continent in Queen Maud Land, the station is now called Druzhnaya III.

A possible drift towards South Georgia

Presently, the biggest concern is that the iceberg might drift towards South Georgia and run aground on its shores. Such a scenario could seriously disturb the millions of animals – seals, penguins and seabirds – that feed in the waters surrounding the island.

Another possible scenario is a drift towards South Africa, which would represent less disturbance for wildlife but not for ships, if A23a were to use maritime routes.

However, even if presently a concern, it is possible that our A23a could meet the same fate as the A68. Itself detached from Larsen C, this 5 800 km2 iceberg had initiated a drift towards South Georgia, raising fears of the worst. Finally, the iceberg broke into smaller chunks before reaching the edge of the island, releasing in its melt a quantity of fresh water equivalent to the volume of water contained in Loch Ness. A discharge that can disrupt ocean currents.

It is therefore likely that the A23a iceberg will suffer the same fate. For the time being, however, he remains under close monitoring.

With global warming, we’re likely to see even more huge icebergs breaking off and drifting away in the future. While such phenomena provide spectacular images, they are of particular interest to scientists, as they provide information on climate and the consequences of global warming in the polar regions.

Mirjana Binggeli, PolarJournal

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