It's big, beautiful and — blue. But this 40-year-old iceberg is about to disappear for good

A 40-year-old berg that was erstwhile the biggest on the major planet is natation into the due south Atlantic Ocean, where it will soon melt into watery oblivion.

But it's going out in style.

A-23a, as it's known, broke off from Antarctica in 1986 and has captured the attention of scientists ever since.

But the world's eyes are now on the behemoth berg thanks to its stunning blue pattern, seen in NASA satellite images captured just after Christmas.

The brilliant hue, however, is a sign that A-23a is in its dying days, as it drifts through what scientists refer to as the "iceberg graveyard," some 2,800 kilometres from where it cracked away. Here's what you should know about the life and legacy of A-23a.

A-23a was once a part of Antarctica's Filchner Ice Shelf, east of the Antarctic peninsula which stretches toward South America.

In 1986, a 4,000 square-kilometre slab cracked away, or calved, forming a tabular iceberg — basically a flat-topped block of ice roughly the size of Rhode Island and weighing more than one trillion tonnes.

But it didn't stray far from home for quite some time.

It became wedged on on the floor of the Weddell Sea until 2020, when it started its fateful journey north along the Antarctic peninsula. It is now, after a few more groundings, bobbing near South Georgia island.

A-23a is now significantly smaller. According to the U.S. National Ice Centre, it has shrunk to about 781 square-kilometres as of Friday after parts of it calved in the warmer waters.

Chris Schuman, a retired scientist, told NASA Earth Observatory that it's unlikely A-23a will survive the Southern Hemisphere's summer.

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Icebergs of any shape and size are quite a sight. But what people find striking about A-23a are those swathes of vivid blue on its surface.

Ted Scambos, a senior research scientist at the University of Colorado in Boulder, told the NASA Earth Observatory that the blue mushy areas are likely meltwater accumulating on the surface of the ice as it slowly breaks it apart.

"You have the weight of the water sitting inside cracks in the ice and forcing them open," he said.

The pattern effect appears to be striations, parallel ridges that formed on the ice over time that "direct the flow of meltwater," National Snow and Ice Data Centre senior research scientist Walt Meier told NASA.

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White and blue might be colours that you expect to see on an iceberg. But what about green? Yellow? Even black?

Scientists investigating why some icebergs in the Weddell Sea turned a brilliant emerald or jade colour say it could be because of ice reflecting the colour of phytoplankton in the water.

Yellow icebergs, according to a 2019 article from National Geographic, may be the result of a dust that's rich with iron oxide, picked up as glacial ice moved over Antarctica's bedrock.

“Ice filters out the red light, and iron oxides filter out the blue light, so green is what's left to escape as refracted sunlight re-emerges from the iceberg,” Steve Warren, an emeritus professor at the University of Washington, told the publication.

Then there was the rare black iceberg spotted last spring off the coast of Labrador.

It's unclear what caused the colour.

It should come as no surprise that the farther icebergs move away from this area of Antarctica that they'll approach warmer waters and begin to disintegrate in an area commonly called the "iceberg graveyard."

The Weddell Sea gyre is a current that circulates clockwise and pulls icebergs northward from this part of Antarctica, along that same path that A-23a followed, and into the Scotia Sea and the Drake Passage.

"Water at this latitude — about 54 degrees south — is generally warmer than the Southern Ocean and deadly for icebergs," said the NASA Earth Observatory. A-23a is located at about that latitude.

A satellite view of the iceberg seen Wednesday on NASA Worldview appears to show a significant chunk of A-23a breaking off.

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Senior Writer

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