Traffic in the vicinity of Antarctica has become a bit trickier now that A23a, the world’s oldest and largest iceberg, has broken free of its watery trap north of the South Orkney Islands and is floating northward on the Antarctic Circumpolar Current.
The annoying thing about icebergs is that, though they are magnificent giant things and have had a significant impact on human events (ask the Titanic), for all their size they are rather ephemeral. Once they calve off from the glaciers that gave them birth, they float north or south, as the case may be, to warmer latitudes where they quickly break up and melt away like memories.
For this reason, signifiers like the world’s largest or oldest are transitory at best. A23a isn’t the largest ever recorded. That title belongs to B-15 that broke away from Antarctica’s Ross Ice Shelf in March 2000. Nor is it the largest most recent berg, which was A-68, which broke from the Larsen Ice Shelf in 2017. However, it is the oldest and largest iceberg at the present time.
A23a
Not that this makes it an ice cube. When last measured, it covered an area of 1,500 miles² (3,900 km²), or twice the size of Greater London, and weighed an estimated trillion tonnes, or as much as 250 billion African elephants.
It’s also the current oldest due to its calving from Antarctica’s Filchner Ice Shelf in 1986, after which it ran aground on the seabed where it remained in chilly storage until it at last floated off into the Weddell Sea in 2020.
Then things got a bit odd. In about April 2024, it encountered a sea phenomenon called a Taylor Column. Put simply, this is a giant eddy caused by a rotating column of water that forms above undersea mountains. A23a was trapped for months in this maelstrom and floated about in erratic circles until recent satellite images showed it finally breaking free and drifting northward toward the sub-Antarctic island of South Georgia, which lies at the South latitude of about 54°.
A23a sat images
The tracking of A63a is of more than scientific interest. Such giant bergs release mineral nutrients as they melt along with vast amounts of fresh water. In the open sea, this can be quite beneficial but if one of these runs aground, as one threatened to do to South Georgia, they can rip up seabeds and flood fresh water into local ecosystems beyond their ability to tolerate.
“We know that these giant icebergs can provide nutrients to the waters they pass through, creating thriving ecosystems in otherwise less productive areas,” said Laura Taylor, a biogeochemist on the British Antarctic Survey’s 2023 BIOPOLE cruise to study the effects of ice sheets. “What we don’t know is what difference particular icebergs, their scale, and their origins can make to that process.
“We took samples of ocean surface waters behind, immediately adjacent to, and ahead of the iceberg’s route. They should help us determine what life could form around A23a and how it impacts carbon in the ocean and its balance with the atmosphere.”
Source: British Antarctic Survey
