The former largest iceberg is turning blue. It’s a bad sign.

One of the oldest icebergs that has ever been tracked is feeling the blues. The megaberg A23a is most likely on its last legs, and has been captured turning blue because of meltwater. The iceberg was once the largest in the world, though it has been drastically shrinking and is now just a fraction of its former size. Given these changes, experts believe it won’t be around for much longer.

Blue period

Iceberg A23a is “sopping with blue meltwater and on the verge of complete disintegration,” said a NASA news release. The space agency’s Moderate Resolution Imaging Spectroradiometer (MODIS) captured an image of the blue waterlogged iceberg at the end of December, then just a day later, an astronaut on the International Space Station took a “photograph showing a closer view of the iceberg” that had an “even more extensive melt pool.”

In parts of the iceberg, the “ponded water appears a deep, vivid blue, suggesting depths of several meters,” said New Scientist. The water volume “probably runs into billions of liters,” which is “enough to fill thousands of Olympic‑sized swimming pools.” The “weight of the water” is “sitting inside cracks in the ice and forcing them open," Ted Scambos, a senior research scientist at the University of Colorado Boulder, said in the NASA release. The images also showed a “thin white line around the outer edge of the iceberg seemingly holding in blue meltwater,” in a “‘rampart-moat’ pattern caused by an upward bending of the iceberg plate as its edges melt at the waterline.”

A23a broke off from Antarctica’s Filchner Ice Shelf in 1986, and it was over 1,500 square miles in size. Today, it is just about 456 square miles, which is a little bigger than New York City. In July, August and September of 2025, the iceberg “saw some sizable breakups as it moved into the Southern Hemisphere’s relatively warm summer conditions,” said Popular Science. It is currently drifting in the South Atlantic between the eastern tip of South America and South Georgia Island.

End of an era

The megaberg will likely not last through the austral summer, or the summer months in the Southern hemisphere. All signs indicate that A23a is “just days or weeks from totally disintegrating as it rides currents that are pushing it toward even warmer waters,” said CBS News. “Warmer air temperatures during this season could also speed up A23a’s demise in an area that ice experts have dubbed a ‘graveyard’ for icebergs.” Climate change will probably lead other icebergs to a similar fate.

Iceberg A23a has been on scientists’ radar for a while. After not moving for a long time, it began to drift in 2020. It got caught in the Antarctic Circumpolar Current, where it was stuck spinning in 2024. When it began moving again, it was on course to crash into an island in 2025, though it didn’t end up making contact. Turning blue is just the next chapter in the megaberg’s long saga.

“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,” Chris Shuman, a retired scientist from the University of Maryland, Baltimore County, said in the NASA release. “A23a 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.”