A colossal Antarctic iceberg separated from the Filchner Ice Shelf nearly four decades ago is displaying vivid signs of its impending demise.
Satellite imagery from Nasa reveals A-23A, once the planet's largest iceberg, has transformed from snowy white to a striking cyan hue.
The dramatic colour change stems from vast meltwater pools accumulating across the ice surface during the austral summer.
Nasa's Terra satellite captured the transformation on Boxing Day with an astronaut aboard the International Space Station photographing an even closer view the following day.
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A-23A was once the planet's largest iceberg
|NASA
Researchers say this blue colouration signals the final chapter for the long-lived megaberg.
At the start of 2025, A-23A measured approximately1405 square miles, making it the world's largest iceberg.
By September, it had diminished to 655 square miles after substantial chunks broke away.
Satellite data from January 9 shows the ice mass has shrunk further to merely 455 square miles.
"I certainly don't expect A-23A to last through the austral summer," said Chris Shuman, a retired Earth scientist formerly with the University of Maryland Baltimore County.
Nasa has declared the iceberg "on the verge of complete disintegration", noting pooled meltwater is forcing open cracks from within.
The mechanics behind A-23A's destruction involve water accumulating in surface depressions and seeping into fractures.
Dr Tedd Scambos, a senior research scientist at the University of Colorado Boulder, explains: "You have the weight of the water sitting inside cracks in the ice and forcing them open."
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Nasa's Terra satellite captured the transformation on Boxing Day
| GETTYDr Shuman describes a "blowout" event where accumulated meltwater became heavy enough to punch through the iceberg's edges, spilling into the surrounding ocean.
After grounding itself in the Weddell Sea for roughly three decades, the iceberg broke free and spent months spinning in an ocean vortex called the Taylor column before drifting northward.
A-23A is currently drifting through the South Atlantic between South America's eastern tip and South Georgia Island, heading toward what scientists call the iceberg graveyard.
The waters there are approximately 3C warmer than Antarctic seas.
The tabular iceberg ranks among the largest and longest-observed on record, having been tracked by researchers for decades since calving in 1986.
"A-23A faces the same fate as other Antarctic bergs, but its path has been remarkably long and eventful. It's hard to believe it won't be with us much longer," Dr Shuman said. "I'm incredibly grateful that we've had the satellite resources in place that have allowed us to track it and document its evolution so closely."
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