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Iceberg B-15

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Northern edge of Iceberg B-15A in the Ross Sea, Antarctica, 29 January 2001

Iceberg B-15 was the largest recorded iceberg by area.[Note 1] It measured around 295 by 37 kilometres (159 by 20 nautical miles), with a surface area of 11,000 square kilometres (3,200 square nautical miles), about the size of the island of Jamaica. Calved from the Ross Ice Shelf of Antarctica in March 2000, Iceberg B-15 broke up into smaller icebergs, the largest of which was named Iceberg B-15-A. In 2003, B-15A drifted away from Ross Island into the Ross Sea and headed north, eventually breaking up into several smaller icebergs in October 2005.[2] In 2018, a large piece of the original iceberg was steadily moving northward, located between the Falkland Islands and South Georgia Island. As of August 2023, the U.S. National Ice Center (USNIC) still lists one extant piece of B-15 that meets the minimum threshold for tracking (70 km2 or 20 sq nmi).[3] This iceberg, B-15AB, measures 20 km × 7 km (11 nmi × 4 nmi); it is currently grounded off the coast of Antarctica in the western sector of the Amery region.[4]

History

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Iceberg B-15A four-year journey, July 2002 to March 2006
Iceberg B-15Z route 2014-2018

In the last weeks of March 2000, Iceberg B-15 calved from the Ross Ice Shelf near Roosevelt Island, Antarctica.[5][6] The calving occurred along pre-existing cracks in the ice shelf.[5] The iceberg measured around 295 km × 37 km (159 nmi × 20 nmi), with a surface area of 10,915 km2 (3,182 sq nmi). Scientists believe that the enormous piece of ice broke away as part of a long-term natural cycle, which occurs every fifty to one hundred years.[5] In 2000, 2002, and 2003, Iceberg B-15 broke up into several pieces, the largest of which, B-15A, covered 6,400 km2 (1,900 sq nmi) of the sea surface.[7]

In November 2003, after the separation from B-15J, B-15A drifted away from Ross Island on the open waters of the Ross Sea. In December 2003, a small knife-shaped iceberg, B-15K (about 300 km2), detached itself from the main body of B-15A and started drifting northward. By January 2005, prevailing currents caused B-15A to drift toward the Drygalski Ice Tongue, a 70-kilometre-long (40 nmi) extension of the land-based David Glacier, which flows through the coastal mountains of Victoria Land.[8] A few kilometres from the ice tongue, the iceberg became stranded on a shallow seamount before resuming its northward course.[9] On 10 April 2005, B-15A collided with the ice tongue, breaking off the tip of the ice tongue; the iceberg seemed unaffected by the collision.[8]

Iceberg B-15A continued to drift along the coast leaving McMurdo Sound. On 27–28 October 2005, the iceberg ran aground off Cape Adare in Victoria Land, generating seismic signals that were detected as far away as the Amundsen-Scott South Pole Station[10][11] and broke into several smaller pieces, the largest of which was still named B-15A (now measuring approximately 1,700 km2 or 500 sq nmi). Three additional pieces were named B-15P, B-15M, and B-15N. Iceberg B-15A then moved farther up north and broke up into more pieces. These were spotted by air force fisheries patrol[clarification needed] on 3 November 2006. On 21 November 2006 several large pieces were seen just 60 km (30 nmi) off the coast of Timaru, New Zealand—the largest measured about 1.8 km (1 nmi), rising 37 m (120 ft) from the surface of the ocean.

As of 2018, four pieces remain that are large enough to be tracked by the National Ice Center (at least 70 km2 or 20 sq nmi).[2] One piece, B-15Z, measures 19 km × 9 km (10 nmi × 5 nmi). It was located in the southern Atlantic Ocean, about 280 km (150 nmi) northwest of South Georgia Island. As it continues its move northward, the speed of melt increases. Most icebergs do not last long this far north.[12]

By 2020, only two pieces remained large enough to track. B-15aa – a direct remnant of B-15z – was drifting to the east of the island of South Georgia, in the south Atlantic Ocean. B-15ab remained among sea ice along the coast of Antarctica south of Africa.[13] In 2021, B-15ab became the last fragment to remain on the US National Ice Center list of tracked icebergs, still grounded off the coast of Antarctica.[4]

Effects on Antarctic ecology

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Researchers installing weather and GPS instruments on Iceberg B-15A, 29 January 2001

On 29 January 2001, researchers from the University of Chicago and the University of Wisconsin installed weather and Global Positioning System instruments on Iceberg B-15A. It was the first time an iceberg had been monitored in this way. The data gathered led to an unprecedented understanding of how giant icebergs make their way through the waters of Antarctica and beyond.

Iceberg B-15A collided with Drygalski Ice Tongue on 10 April 2005, breaking off an eight-square-kilometre (2+1⁄4 sq nmi) section of the ice tongue. Antarctic maps needed to be redrawn.

B-15A prevented ocean currents and winds from assisting in the 2004–2005 summer break-up of the sea ice in McMurdo Sound, and was an obstacle to the annual resupply ships to three research stations. The floe was expected[needs update] to cause a catastrophic decline in the population of Adélie penguins, as it added considerable distances which parent penguins must travel back from the sea to their chicks. Weddell seals and skuas are also inhabitants of McMurdo Sound and their populations may have been affected as well.

On 21 October 2005 a large storm in the Gulf of Alaska generated a trans-Pacific Ocean swell that may have contributed to breaking B15-A into many pieces on 27 October 2005.[10] The swell travelled 13,500 km (7,300 nmi) from Alaska to Antarctica over six days. Scientists are studying this event as an example of how weather in one area can have effects in other parts of the world, and with concern over the effects on global warming.[14]

A more detailed study in 2010, however, shows that the iceberg breakup was principally caused by repeated grounding with near-coastal bathymetry near Cape Adare, Victoria Land.[11]

Satellite images

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Iceberg B-15A drifting toward the Drygalski Ice Tongue before the collision, 2 January 2005 (NASA)
Iceberg B-15 after break-up, showing B-15M, B-15N, and B-15P, 31 October 2005 (DMSP)

See also

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References

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Notes

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  1. ^ Iceberg B-15 is the largest iceberg recorded by satellite photography. In 1956, an iceberg in the Antarctic was reported to measure an estimated 333 km × 100 km (180 nmi × 54 nmi). Recorded before the era of satellite photography, the 1956 iceberg's estimated dimensions are less reliable.[1]

Citations

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  1. ^ Goering, Laurie (24 March 2000). "Mammoth Iceberg Is Born In Antarctic". Chicago Tribune. Retrieved 18 February 2014.
  2. ^ a b Specktor, Brandon (8 June 2018). "Antarctica's Largest Iceberg Is About to Die ... Near the Equator". Space.com. Retrieved 1 August 2019.
  3. ^ "Antarctic Iceberg Data". US National Ice Center.
  4. ^ a b "Icebergs" (PDF). US National Ice Center. 6 August 2021.
  5. ^ a b c "Massive Iceberg Peels Off from Antarctic Ice Shelf". National Science Foundation. 22 March 2000. Retrieved 17 February 2014.
  6. ^ "Biggest iceberg tracked from space". The ATSR Project. 9 May 2000. Retrieved 17 February 2014.
  7. ^ Arrigo, Kevin R.; Van Dijken, Gert L. (January–February 2004). "Annual changes in sea-ice, chlorophyll a, and primary production in the Ross Sea, Antarctica". Deep-Sea Research Part II: Topical Studies in Oceanography. 51 (1–3): 117–138. Bibcode:2004DSRII..51..117A. doi:10.1016/j.dsr2.2003.04.003.
  8. ^ a b "Pile-up as berg hits Antarctica". BBC. 19 April 2005. Retrieved 17 February 2014.
  9. ^ Bhattacharya, Shaoni (19 April 2005). "World's largest iceberg 'goes bump in the night'". New Scientist. Retrieved 17 February 2014.
  10. ^ a b MacAyeal, Douglas R.; et al. (12 September 2006). "Transoceanic wave propagation links iceberg calving margins of Antarctica with storms in tropics and Northern Hemisphere". Geophysical Research Letters. 33 (17): L17502. Bibcode:2006GeoRL..3317502M. doi:10.1029/2006gl027235.
  11. ^ a b Martin, Seelye; Drucker, Robert; Aster, Richard; Davey, Fred; Okal, Emile; Scambos, Ted; MacAyeal, Douglas (2010). "Kinematic and seismic analysis of giant tabular iceberg breakup at Cape Adare, Antarctica". Journal of Geophysical Research. 115 (B6): B06311. Bibcode:2010JGRB..115.6311M. doi:10.1029/2009jb006700.
  12. ^ Eleanor Imster (11 June 2018). "End of the journey for iceberg B-15?". Retrieved 22 July 2019.
  13. ^ Scott Sutherland (28 April 2020). "New satellite images reveal Iceberg A-68's days are numbered". Retrieved 20 May 2021.
  14. ^ Harris, Richard (5 October 2006). "Alaskan Storm Plays Role of Butterfly for Antarctica". National Public Radio. Retrieved 17 February 2014.

Further reading

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  • Stone, Gregory S. (2003). Ice Island : Expedition to Antarctica's Largest Iceberg. Boston, Massachusetts: New England Aquarium Press, National Geographic Society. ISBN 1593730179. OCLC 52739140.
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