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Ecology & Environment
Mahesh

12/08/24 07:44 AM IST

World’s largest iceberg is stuck spinning in circles

In News
  • For more than 30 years, the world’s largest iceberg was stuck in the Antarctic. 
A23 iceberg
  • The iceberg is spinning near the South Orkney Islands, about 375 miles northeast of the Antarctic Peninsula, “maintaining a chill 15 degree rotation per day,” the British Antarctic Survey.
  • It’s basically just sitting there, spinning around, and it will very slowly melt as long as it stays there.
  • A23a has been embroiled in drama since the start, a trait it picked up from its parent-berg.
  • A23, which was even bigger than A23a, was one of three icebergs that broke off, or calved, from the Filchner Ice Shelf in 1986.
  • At the time of the calving, A23 was home to a Soviet Union research center and researchers eventually had to abandon the base.
  • A23a broke off later that year and hit bottom in the Weddell Sea, where it would remain for 34 more years.
  • In 2020, A23a finally freed itself, and in December, it began to move out of Antarctic waters on a long meander through the Southern Ocean.
  • It took Brearley and a research vessel almost an entire day to circle it during a visit in December. They were awestruck.
  • But by spring, A23a caught the spins. Using satellite imagery, the British Antarctic Survey first observed the iceberg spinning in April.
  • Large Antarctic icebergs are designated by A, B, C and D depending on where in Antarctica they originate, and they receive a number only once they’ve reached a big enough size.
  • Their sequential order shows how long A23a has topped the list of world’s biggest icebergs: A76 calved in 2021, for instance, but melted two years later.
Spinning of A23
  • The iceberg is in an area of the Southern Ocean known as Iceberg Alley, a popular spot for icebergs.
  • Typically, large icebergs move through quickly and get sucked into the Antarctic Circumpolar Current, the largest ocean current in the world.
  • The blocks of ice eventually get shot out eastward to warmer waters, where they begin to melt and disintegrate.
  • Brearley described the transition as “a warm bath of water” only a couple of degrees above freezing.
  • Instead, the gigantic iceberg got caught in what’s known as a Taylor column, a current that forms around seamounts. Standard flow diverges around the underwater mountain and creates a stagnant cylinder of fluids above the seamount, slowly rotating the water counterclockwise around the bump.
  • The bump A23a is swimming over is about 100 kilometers across (about 62 miles) and rises up from the deep sea floor to a height of about 1,000 meters (3,280 feet).
  • Melting icebergs that originate from floating ice shelves like A23a do not themselves significantly contribute to global sea level rise, said Brearley, because the ice is already floating in the ocean.
  • Climate scientists are concerned that the deterioration of large portions of ice shelves will make the continent’s glaciers more vulnerable to warming.
  • Brearley pointed to a 2015 study that observed a robotic float, part of a fleet of instruments that drift in ocean currents to measure water temperature, trapped in a Taylor column for four years just to the northeast of A23a’s current location.
  • If A23a spends an extended time in the vortex, the iceberg could melt significantly and affect plankton and other organisms in the marine food chain in the area.
Source- Indian Express

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