Screenshot from a NOAA satellite system monitoring iceberg A23a drifting near the Weddell Sea off the Antarctic Peninsula in February.
//NOAA Joint Polar Satellite System
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//NOAA Joint Polar Satellite System
The world’s largest iceberg, A23a, got stuck again.
For more than 30 years, this massive frozen mass the size of Rhode Island has been stranded on the seafloor in Antarctic coastal waters. It was finally freed in 2020 and began its journey to the high seas last winter.
But months into the A23a journey, onlookers were shocked by what they saw: The iceberg was spinning.
The British Antarctic Survey noticed through satellite images that starting in January, giant icebergs were spinning near the South Orkney Islands, about 375 miles from the Antarctic Peninsula. According to the investigation, the A32a maintained a “15-degree cold rotation every day.”
Its dance movements are likely caused by a phenomenon in fluid mechanics called Taylor columns. It is essentially a rotating cylinder that forms when there are obstacles in the flow. In other words, A23a is trapped in a kind of ocean vortex.
Till Wagner, a professor at the University of Wisconsin-Madison who studies ice-climate interactions, said he has never seen a real-life example of this phenomenon on such a large scale.
“You know, you can easily make these Taylor columns in a spin-pot experiment in the laboratory. But it’s really rare to see it like this on a geophysical scale,” he said.
There’s still a lot to understand about how Taylor columns affect behemoths like A23a. It’s unclear how often Taylor columns form in the ocean and how often icebergs get trapped in them.
In the case of A23a, it’s anyone’s guess how long it will remain spinning in the vortex. The iceberg is melting as it spins, and Wagner is curious about how it will affect life in the surrounding ecosystem, such as phytoplankton.
“It will be interesting to see if next spring we have more active phytoplankton in that location,” he said.
The origin of Iceberg A23a dates back to 1986, when three icebergs broke off from the leading edge of the Filchner Ice Shelf. A23a has been stuck on a sandbar in shallow water for decades. In 2020, the main part of A23a released itself and finally began floating into the Southern Ocean in November.
It is expected to move north over the next year, reaching warmer waters where it will melt and break up rapidly. Now the fate of A23a is even more uncertain.
