It’s the mother of all break-ups.
The life of one of the world’s largest and longest lasting icebergs is finally coming to an end after it drifted away from Antarctica nearly 40 years ago.
In March, we flew over megaberg A23a after it ran aground off South Georgia, one of the UK’s most remote overseas territories.
Back then it was a trillion-tonne block of ice more than twice the size of Greater London.
There were concerns its collapse close to the island might endanger globally significant populations of penguins, seals and seabirds.
But a few months later the iceberg floated free and began drifting again, looping around to the north of South Georgia where now, in the Antarctic spring, it is finally falling apart.
“It’s been exposed to warmer waters for quite a long time,” said Andrew Meijers, an oceanographer at the British Antarctic Survey in Cambridge.
“So it’s pretty much rotted through.”
Satellite images from the last few days now reveal “we’ve got really big chunks breaking off,” said Meijers.
The largest piece to come away in the last few days is 80 sq km – a colossal iceberg in its own right.
A23a is still 1,700sq km – larger than London – but will now rapidly disappear.
‘It’s not going to last for more than a few weeks’
“It’s not going to last in that chunk format for more than a few weeks or a month at most,” predicts Meijers.
As the iceberg breaks up, the surface area of pieces exposed to warmer water increases, accelerating its melting.
It’s also now caught in a current carrying it northwards, into increasingly milder temperatures.
The rapid break-up of A23a means it’s unlikely to pose a risk to wildlife on South Georgia but will represent a temporary hazard to shipping – especially as pieces become too small to monitor by satellite.
Last week, RAF Operation Cold Stare, using the aircraft that flew us over the iceberg in spring, overflew A23a again.
One of its roles is to map icebergs that may threaten shipping – largely fishing vessels and Antarctica-bound cruise ships in a remote corner of the Southern Ocean.
During our flight over A23a it was hard to imagine a block of ice so large disappearing so fast. But even then we could see cracks several kilometres long running through it.
All along its edges were cathedrals-sized caverns and vast “terraces” of ice at sea-level resulting from pounding by waves that rapidly crumble into the ocean.
Satellite records of large icebergs don’t go back long enough for scientists to know whether they are becoming more frequent as the planet warms.
But there’s strong evidence the West Antarctic Ice Sheet, where A23a and many of its predecessors began their lives, is melting increasingly fast.
Antarctica is losing around 150 billion tonnes of water each year, half of which is carried away in the form of icebergs.
Read more:
The impact of the world’s biggest iceberg
Your iceberg A23a questions answered
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Antarctic melting is being closely monitored by scientists concerned about the impact it is having on major ocean currents that underpin global climate – a potential “tipping-point” in planetary warming.
As it has shrunk, A23a has now ceded its world heavyweight title to the 3000sq km iceberg D15a, which is aground on the coast of Antarctica close to where it broke off in 1992.
