THE’iceberg A23awhich broke off from an ice shelf on the Antarctic ice cap way back in 1986, is the largest in the worldwith its extension of approx 3672 km2 (measured in August, in the middle of the southern winter), a surface area slightly larger than that of the Aosta Valley, and a mass of approximately 1000 billion tons. For decades it remained anchored to the seabed and only in 2020 did it start moving again only to be blocked again due to an ocean vortex. Now this huge block of ice has begun its journey again drifts in the Southern Ocean. The Antarctic Circumpolar Current will probably push it to the coasts ofSouth Georgia Islandwhere hotter water is expected to cause it to fragment and melt. The movement and melting of the iceberg will be continuously monitored to understand how it will affect marine ecosystems and the global carbon cycle.
The story of the A23a iceberg
Iceberg A23a broke off in 1986 Filchner-Ronne ice shelfa huge floating mass that extends above the ocean from the Antarctic ice sheet. After having traveled only a few hundred kilometres, it remained stranded at the bottom of the river for over 30 years Weddell Seaclose to Antarctica. Over time its dimensions have reduced to the point of allowing it to free itself from the seabed and, after the first modest movements of 2020, in 2023 the iceberg moved more rapidly northward driven by the currents.
At this point, however, another unforeseen event occurred which stopped its journey again: near the South Orkney Islands north-east of the Antarctic Peninsula the iceberg encountered the “Taylor column”, a vortex of water that forms above a underwater mountaincapable of capturing any object located above it. The result was that for months the iceberg remained stationary at that point, rotating on itself. Now its drift has begun again and according to researchers the Antarctic Circumpolar Current will carry it to the island of South Georgia.
The fate of the A23a iceberg and the implications of its meltdown
Once it reaches the coast of South Georgia Island, the iceberg will encounter warmer waters that will lead it to fragment and merge. The researchers monitoring it will study the consequences that its fusion will have on Global oceanic carbon cycles And of nutrients and on marine ecosystems. With the aim of understanding these mechanisms, last year samples of sea water had already been taken around the A23a iceberg, during the Biopole mission. Laura Taylor, a biogeochemist on the mission, said: “We know that these giant icebergs can provide nutrients to the waters they pass through, creating thriving ecosystems in otherwise less productive areas.” What is less clear is how the size of the icebergs affects the process.
Even if its dimensions are exceptional, the A23a iceberg is only one of the countless large blocks of ice that are increasingly breaking off from the Antarctic shelves: in May 2024, for example, theiceberg A-83extended 375 km2. TO February 2023 has been registered lowest Antarctic sea ice extent in 44 years of data, with a 38% loss of ice compared to the 1979-2022 average for the month of February. This loss has countless negative effects, since the Antarctic ice sheet is the main driver of global ocean circulation and plays a fundamental role in regulating the planet’s temperature.
