Screenshot of the National Oceanic and Atmospheric Administration’s satellite system tracking iceberg A23a in February as it drifted around the Weddell Sea near the Antarctic Peninsula.
//National Oceanic and Atmospheric Administration’s Joint Polar Satellite System
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//National Oceanic and Atmospheric Administration’s Joint Polar Satellite System
The world’s largest iceberg A23a is stuck again.
For more than 30 years, the massive iceberg — roughly the size of Rhode Island — was stranded on the seabed in Antarctica’s coastal waters. It finally broke free in 2020 and began heading out to sea last winter.
But after a few months of A23a’s movement, onlookers were amazed by what they saw: the iceberg was spinning.
Using satellite imagery, the British Antarctic Survey has spotted the giant iceberg rotating near the South Orkney Islands, about 375 miles off the Antarctic Peninsula, since January. According to the survey, A32a maintain “change temperature 15 degrees every day.”
Its jumping movements may be due to a phenomenon in fluid mechanics called a Taylor column. It is essentially a rotating cylinder that forms when there is an obstruction 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 how ice interacts with climate, said he had never seen a real-world example of the phenomenon on such a large scale.
“You know, you can easily create these Taylor Columns in a rotating tank experiment in the lab. But to see it on a geophysical scale like this is really rare,” he said.
There is a lot to understand about how Taylor Columns might affect a monster like A23a. It is unclear how often Taylor Columns form in the ocean and how often icebergs get trapped in them.
In the case of A23a, no one can predict how long it will stay in the spin. The iceberg is also melting as it spins, and Wagner is curious to see how it will affect life in the surrounding ecosystem, like phytoplankton.
“It will be interesting to see if next spring we see more phytoplankton blooms there,” he said.
The origins of Iceberg A23a date back to 1986 when Leading edge of the Filchner Ice Shelf broke off three icebergs. For decades, A23a was stuck on a sandbank in shallow water. In 2020, most of A23a broke free, and in November it finally began drifting into the Southern Ocean.
It is expected to move north over the next year, into warmer waters, where it will quickly melt and break apart. For now, A23a’s fate is somewhat uncertain.
