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15-12-2023
ANTARCTICA’S COASTLINE: Scientists now have good numbers to describe the true scale of the world’s biggest iceberg, A23a.
Satellite measurements show the frozen block has a total average thickness of just over 280m (920ft).
Combined with its known area of 3,900 sq. km (1,500 sq. miles), this gives a volume of roughly 1,100 cubic km and a mass just below a trillion tones.
The iceberg, which calved from the Antarctic coast in 1986, is about to drift beyond the White Continent.
It has reached a critical point in its journey, researchers say, with the next few weeks likely to decide its future trajectory through the Southern Ocean.
To put the new thickness data in some context, London skyscraper 22 Bishopsgate is 278m tall bettered, in the UK, by only the 310m Shard tower but A23a is also more than twice the area of Greater London, giving it an overall profile much like that of a credit card.
The measurements of A23a come from the European Space Agency’s CryoSat-2 mission.
This veteran spacecraft carries a radar altimeter able to sense how much of a berg’s bulk is above the waterline.
Using information about the density of ice, it is then possible to determine how much must be submerged.
“Altimetry satellites like CryoSat-2, which measure the distance to the iceberg surface and to the sea surface, allow us to monitor iceberg thickness from space,” Dr Anne Braakmann-Folgmann, from the University of Tromso, the Arctic University of Norway, told media.
“They also enable us to watch the iceberg thinning as it gets exposed to warmer ocean waters and “together with knowledge of the sea-floor topography, we know where an iceberg will ground or when it has thinned enough to be released again.”
Born in a mass breakout of bergs from the Filchner Ice Shelf, in the southern Weddell Sea, A23a was almost immediately stuck in shallow bottom muds to become an “ice island” for more than three decades and the CryoSat data can now explain why.
The berg is not a uniform block some parts are thicker than others.
CryoSat indicates one section in particular has a very deep keel, which in 2018, had a draft, the submerged portion of an iceberg of almost 350m.
And it is this section that anchored A23a for so long.
Satellite images even show the surface crevasses that opened directly above the keel as a result of the violent collision with the sea-floor. (Int’l News Desk)
