The End Is Near For Our Intrepid Iceberg A23a

Credit: NASA

I bet you weren't expecting to hear the name A23a again, but the iceberg has once again made the news. It's been a long journey for the utterly massive block of ice, but at long last A23a's time has come. Satellite images shows blue meltwater all over its surface, and it also seems as if A23a has sprung a leak, with the weight of the water on top punching a hole through the ice to the ocean below. It is not expected to last through the Southern Hemisphere summer, which means it's only got a couple months at most.

Since I've covered A23a twice before (here and here), I won't go into too many details into its history, but it is nice that it was able to reach its 40th year. Considering how the planet is continuing to warm, I don't imagine we'll see future icebergs get so old.

You Spin My Iceberg Right 'Round

(For full effect, here's a link to the song for some appropriate mood setting.)

The world's largest iceberg is spinning right 'round, like a record. And it'll be doing so for a long time.

You'd probably like some context to that statement.

Way back in 1986, an enormous iceberg, even larger than Rhode Island, split off from Antarctica's Filchner-Ronne ice shelf. Dubbed A23a (not a particularly catchy name), it almost immediately hit the bottom of the sea, sitting in place for over 30 years until 2020. At that point, A23a melted enough to drift free, resuming a long journey north to join the Antarctic Circumpolar Current. And while A23a is certainly much larger than your average iceberg, its fate would eventually be the same, drifting along until finally the last ice melted.

But before all that could happen, something rather amusing happened: A23a passed directly over a seamount. And not just any seamount, but the Pirie Bank Seamount, which juts out about a kilometer above the surrounding abyssal plain. Crucially, this seamount is slightly larger than A23a (roughly 60 by 60 kilometers), which made the iceberg the perfect size to get caught in something called a Taylor column – a vortex formed by ocean currents hitting and flowing around the seamount. 

The end result is something scientists say they've never seen before, as this enormous iceberg spins round and round (completing one rotation in roughly 25 days), trapped by the currents flowing around it. Not only did the A23a have to hit the bulls-eye with quite literally the entire Southern Ocean to play with, the conditions around the seamount also had to be correct (the water had to be flowing at certain speed, not too fast or to slow) in order to capture the enormous block of ice trundling overhead.

While the conditions keeping A23a in place will eventually end, releasing it from its 80s pop music prison, it will likely take a few years before the iceberg can continue on its merry way. Until then, we need to find the world's largest needle ... what? It's spinning like a record, maybe we ought to treat it like one. I'm all for guitar solos longer than your average geologic epoch.