Iceberg A-68

Iceberg A-68 was a giant tabular iceberg adrift in the South Atlantic, having calved from Antarctica's Larsen C ice shelf in July 2017.[1][2][3] By 16 April 2021, no significant fragments remained.[4]

A-68A on 18 November 2020

Iceberg A-68 on 20 July 2017
The drift of Iceberg A-68A from 1 May 2018 to 26 August 2018

With a surface area of 5,800 square kilometres (2,200 sq mi), twice the size of Luxembourg, over a quarter the size of Wales, and larger than Delaware,[5] it was one of the largest recorded icebergs, the largest being B-15 which measured 11,000 square kilometres (4,200 sq mi) before breaking up. The calving of A-68 reduced the overall size of the Larsen C shelf by 12 percent.[5][6]

Historical data shows that many icebergs that break off from the Antarctic Peninsula reach South Georgia and the South Sandwich Islands.[7]

The name "A-68" was assigned by the US National Ice Center. It broke into parts with the mother berg dubbed A-68A. The larger child icebergs were designated in order of birthing, as A-68B, A-68C, A-68D, A-68E, A-68F, and in January 2021, splitting almost in half to birth A-68G. On 30 January 2021, Iceberg A-68A broke into other icebergs called A-68H, A-68I, A-68J, A-68K, A-68L, A-68M.

History and recent developments

A-68 was part of Larsen C, a section of the Larsen Ice Shelf. Scientists found the crack beginning to form in November 2016. Scientists assess that A-68 "didn't just break through in one clean shot, [but] it formed a lace-network of cracks first."[5] The resulting iceberg was around 175 km long and 50 km wide, 5,800 km² in area, 200 m thick and weighed an estimated one trillion tonnes.[8][5]

Satellite images from the ESA and EU's Copernicus Program show that as the iceberg moved, it was gradually shrinking and splintering, forming more icebergs in the process.[9]

Scientists are looking into the possibility of the ice shelf collapsing as a result of the split with A-68, or whether the iceberg was the "cork" for Larsen C that allows ice to flow more freely into the sea, thereby contributing to rising sea levels.[10]

Post November 2017, satellite images showed that A-68 was slowly drifting northward, with a widening gap to the main shelf. The gap was approximately five kilometers (3.1 miles) wide and contained a thin layer of loose, floating ice and a cluster of more than 11 'smaller' bergs, one much larger than the others.

A British expedition on RRS James Clark Ross intended to sample the marine life at the A-68 cleavage line in March 2018, but had to turn back due to thick sea ice.[11] During 2018, A-68 continued to drift northwards.[12] In 2018 or 2019, a large chunk almost 14 km × 8 km (9 miles × 5 miles) broke off and was named A-68B, with the mother iceberg now being A-68A.[13]

On 6 February 2020, A-68A began moving into open waters.[14] On 23 April 2020, a chunk measuring about 175 sq. km. (70 sq. mi.) broke off the iceberg and was named A-68C.[15]

On 4 November 2020, it was reported that A-68A was approaching South Georgia Island and that there was a strong possibility that the iceberg might run aground on the shallower continental shelf near the island, posing a grave threat to local penguins and seals. A spokesman from the British Antarctic Survey stated that the iceberg could become stuck for a number of years, causing disruption to wildlife and the local fishing industry.[16]

On 9 December 2020, the Royal Air Force released video footage of A-68A, 150 km off South Georgia. The RAF conducted reconnaissance flights over the iceberg on 18 November and 5 December 2020.[17]

As of 17 December 2020, a part of the iceberg was just 50 km (31 mi) from South Georgia, but the concern seemed to have lessened. National Geographic reported that "[s]cientists expect the iceberg ... to either anchor in the shallow waters around the island or move past it in the coming days."[18] On this date it was also reported that a corner had been knocked off A-68A, most likely due to impact with the seabed.[19] The new free floating iceberg has been designated A-68D.[20]

On 22 December 2020, images from ESA's Sentinel-1 radar satellite showed that A-68A had experienced a major break-up. Two of the larger fragments were named A-68E and A-68F.[21] A modeling study demonstrated that this break-up was likely triggered when part of A-68A became positioned within stronger ocean currents than the rest of the berg, generating enough tension along its body to break it into pieces.[22]

On 28 January 2021, Sentinel-1 discovered that the southern third of A-68A had broken away. The new segment was named A-68G, with an area of around 950 square kilometres (370 sq mi). The imagery shows these two bergs around 135 km south-east of South Georgia drifting close together.[23][24]

On 30 January 2021, Iceberg A-68A broke up into other icebergs called A-68H, A-68I, A-68J, A-68K, A-68L, and A-68M.[25][26]

On 15 February 2021, it was reported that British scientists had arrived at the remnants of A-68A, and had deployed a robotic glider to measure seawater salinity, temperature and chlorophyll close to the remaining blocks of ice to ascertain effects on local marine life.[27]

On 16 April 2021, the largest fragment was down to 3 nautical miles in length and the U.S. National Ice Center, which names, tracks, and documents Antarctic icebergs, discontinued tracking,[4] as the Center only studies icebergs that are at least 20 sq. nautical miles, or that measure 10 nautical miles on the longest axis.[28]

  • Radar imagery from Sentinel-1B taken on 12 July 2017, showing the complete break
    Radar imagery from Sentinel-1B taken on 12 July 2017, showing the complete break
  • A-68 on 12 July 2017
    A-68 on 12 July 2017
  • Close-up of A-68 on 20 July 2017
    Close-up of A-68 on 20 July 2017
  • Close-up of A-68 on 9 December 2019
    Close-up of A-68 on 9 December 2019
  • A-68A location on 9 February 2020
    A-68A location on 9 February 2020
  • MS World Explorer at A-68A (with spyhopping humpback whale) in the Weddell Sea, 10 March 2020
    MS World Explorer at A-68A (with spyhopping humpback whale) in the Weddell Sea, 10 March 2020
  • A-68A in open waters on 5 July 2020
    A-68A in open waters on 5 July 2020

References
  1. "Larsen C calves trillion ton iceberg". Project MIDAS. 12 July 2017. Archived from the original on 12 July 2017. Retrieved 12 July 2017.
  2. "Giant iceberg splits from Antarctic". BBC. 12 July 2017.
  3. "Massive iceberg breaks away from Antarctica". CNN. 12 July 2017. Retrieved 13 July 2017.
  4. Amos, Jonathan (18 April 2021). "A68: Iceberg that became a social media star melts away". BBC News. Retrieved 18 April 2021.
  5. Davis, Nicola (2 August 2017). "What happened next to the giant Larsen C iceberg?". The Guardian. ISSN 0261-3077. Retrieved 2 August 2017.
  6. McKie, Robin (31 January 2021). "Extraordinary voyage: on the trail of the trillion-tonne runaway iceberg". The Observer. ISSN 0029-7712. Retrieved 31 January 2021.
  7. Mosher, Dave (12 July 2017). "Where Antarctic iceberg from Larsen C shelf might go in Southern Ocean". Business Insider. Retrieved 21 July 2017.
  8. "A brief history of A68, the world's largest iceberg". European Geosciences Union. Climate Change & Cryosphere. 25 September 2020.
  9. Dvorsky, George. "Antarctica's massive iceberg is starting to disintegrate". Gizmodo. Retrieved 2 August 2017.
  10. Becker, Rachel (2 August 2017). "Cracks are still spreading where that massive Antarctic iceberg broke free". The Verge. Retrieved 2 August 2017.
  11. Amos, Jonathan (2 March 2018). "Mission to giant A-68 berg thwarted by sea-ice". BBC News. Retrieved 12 April 2018.
  12. Brandon, Mark. "A trillion tonnes of ice on the move: Iceberg A-68A". Mallemaroking. Retrieved 31 August 2018.
  13. Irving, Michael (13 July 2020). "Satellites show huge Antarctic iceberg drifted 1,000 km in three years". New Atlas. Retrieved 13 July 2020.
  14. Amos, Jonathan (5 February 2020). "World's biggest iceberg makes a run for it". BBC News. Retrieved 25 July 2020.
  15. Amos, Jonathan (23 April 2020). "Is the world's biggest iceberg about to break up?". BBC News. Retrieved 28 April 2020.
  16. Amos, Jonathan (4 November 2020). "A68 iceberg on collision path with South Georgia". BBC News. Retrieved 4 November 2020.
  17. Amos, Jonathan (9 December 2020). "RAF releases video of world's biggest iceberg". BBC News. Retrieved 13 December 2020.
  18. "The world's largest iceberg is headed for South Georgia—and its wildlife". National Geographic. 17 December 2020. Retrieved 18 December 2020.
  19. Amos, Jonathan (17 December 2020). "Giant iceberg A68a prangs seabed and loses corner". BBC News. Retrieved 18 December 2020.
  20. Garrison, Cassandra (17 December 2020). "Massive iceberg pivots, breaks, near south Atlantic penguin colony island". Reuters. Retrieved 18 December 2020.
  21. Amos, Jonathan (22 December 2020). "Giant iceberg A68a shatters into large fragments". BBC News. Retrieved 22 December 2020.
  22. Huth, Alex; Adcroft, Alistair; Sergienko, Olga; Khan, Nuzhat (21 October 2022). "Ocean currents break up a tabular iceberg". Science Advances. 8 (42): eabq6974. doi:10.1126/sciadv.abq6974. ISSN 2375-2548.
  23. "Größter Eisberg der Welt bricht entzwei". science.ORF.at (in German). 29 January 2021. Retrieved 29 January 2021.
  24. Amos, Jonathan (28 January 2021). "Split signals end for remnant of Antarctic iceberg A68a". BBC News. Retrieved 29 January 2021.
  25. "Once the World's Largest Iceberg, A68a Is Now a Shattered Mess". Earther. 5 February 2021. Retrieved 9 February 2021.
  26. "The A-68 story". www.esa.int. Retrieved 9 February 2021.
  27. Amos, Jonathan (15 February 2021). "Robots deployed at A68A mega-iceberg remnants". BBC News. Retrieved 15 February 2021.
  28. Coles, Amy (18 April 2021). "World's largest iceberg A68a melts away after three years, satellite data shows". Sky News. Retrieved 20 April 2021.
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