With a surface area of 5,800 square kilometres (2,200sqmi), 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 (4,200sqmi) before breaking up. The calving of A-68 reduced the overall size of the Larsen C shelf by 12 percent.[5][6]
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 LarsenC, a section of the Larsen Ice Shelf. Scientists found the crack beginning to form in November2016. 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 175km (574,000ft) long and 50km (160,000ft) wide, 5,800km2 (2,200sqmi) in area, 200m (660ft) 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 LarsenC 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.[citation needed]
A British expedition on RRSJames Clark Ross intended to sample the marine life at the A-68 cleavage line in March2018, 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 6February 2020, A-68A began moving into open waters.[14] On 23April 2020, a chunk measuring about 175 sq. km.(70 sq. mi.) broke off the iceberg and was named A-68C.[15]
On 4November 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 9December 2020, the Royal Air Force released video footage of A-68A, 150km off South Georgia. The RAF conducted reconnaissance flights over the iceberg on 18November and 5December 2020.[17]
As of 17December2020[update], a part of the iceberg was just 50km (31mi) 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 22December 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 28January 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 (370sqmi). The imagery shows these two bergs around 135km south-east of South Georgia drifting close together.[23][24]
On 30January 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 15February 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 16April 2021, the largest fragment was down to 3nautical 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 20sq. nautical miles, or that measure 10nautical miles on the longest axis.[28]
Gallery
Radar imagery from Sentinel-1B taken on 12July 2017, showing the complete break
An iceberg is a piece of freshwater ice more than 15 meters long that has broken off a glacier or an ice shelf and is floating freely in open water. Smaller chunks of floating glacially derived ice are called "growlers" or "bergy bits". Much of an iceberg is below the water's surface, which led to the expression "tip of the iceberg" to illustrate a small part of a larger unseen issue. Icebergs are considered a serious maritime hazard.
The climate of Antarctica is the coldest on Earth. The continent is also extremely dry, averaging 166 mm (6.5 in) of precipitation per year. Snow rarely melts on most parts of the continent, and, after being compressed, becomes the glacier ice that makes up the ice sheet. Weather fronts rarely penetrate far into the continent, because of the katabatic winds. Most of Antarctica has an ice-cap climate with extremely cold and dry weather.
The Ross Ice Shelf is the largest ice shelf of Antarctica. It is several hundred metres thick. The nearly vertical ice front to the open sea is more than 600 kilometres (370 mi) long, and between 15 and 50 metres high above the water surface. Ninety percent of the floating ice, however, is below the water surface.
An ice shelf is a large platform of glacial ice floating on the ocean, fed by one or multiple tributary glaciers. Ice shelves form along coastlines where the ice thickness is insufficient to displace the more dense surrounding ocean water. The boundary between the ice shelf (floating) and grounded ice is referred to as the grounding line; the boundary between the ice shelf and the open ocean is the ice front or calving front.
The Filchner–Ronne Ice Shelf or Ronne–Filchner Ice Shelf is an Antarctic ice shelf bordering the Weddell Sea.
South Georgia is an island in the South Atlantic Ocean that is part of the British Overseas Territory of South Georgia and the South Sandwich Islands. It lies around 1,400 kilometres (870 mi) east of the Falkland Islands. Stretching in the east–west direction, South Georgia is around 170 kilometres (106 mi) long and has a maximum width of 35 kilometres (22 mi). The terrain is mountainous, with the central ridge rising to 2,935 metres (9,629 ft) at Mount Paget. The northern coast is indented with numerous bays and fjords, serving as good harbours.
The Larsen Ice Shelf is a long ice shelf in the northwest part of the Weddell Sea, extending along the east coast of the Antarctic Peninsula from Cape Longing to Smith Peninsula. It is named after Captain Carl Anton Larsen, the master of the Norwegian whaling vessel Jason, who sailed along the ice front as far as 68°10' South during December 1893. In finer detail, the Larsen Ice Shelf is a series of shelves that occupy distinct embayments along the coast. From north to south, the segments are called Larsen A, Larsen B, and Larsen C by researchers who work in the area. Further south, Larsen D and the much smaller Larsen E, F and G are also named.
The Brunt Ice Shelf borders the Antarctic coast of Coats Land between Dawson-Lambton Glacier and Stancomb-Wills Glacier Tongue. It was named by the UK Antarctic Place-names Committee after David Brunt, British meteorologist, Physical Secretary of the Royal Society, 1948–57, who was responsible for the initiation of the Royal Society Expedition to this ice shelf in 1955.
Iceberg B-15 was the largest recorded iceberg by area. It measured around 295 by 37 kilometres, with a surface area of 11,000 square kilometres, 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. 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. This iceberg, B-15AB, measures 20 km × 7 km ; it is currently grounded off the coast of Antarctica in the western sector of the Amery region.
The Amery Ice Shelf is a broad ice shelf in Antarctica at the head of Prydz Bay between the Lars Christensen Coast and Ingrid Christensen Coast. It is part of Mac. Robertson Land. The name "Cape Amery" was applied to a coastal angle mapped on 11 February 1931 by the British Australian New Zealand Antarctic Research Expedition (BANZARE) under Douglas Mawson. He named it for William Bankes Amery, a civil servant who represented the United Kingdom government in Australia (1925–28). The Advisory Committee on Antarctic Names interpreted this feature to be a portion of an ice shelf and, in 1947, applied the name Amery to the whole shelf.
Thwaites Glacier is an unusually broad and vast Antarctic glacier located east of Mount Murphy, on the Walgreen Coast of Marie Byrd Land. It was initially sighted by polar researchers in 1940, mapped in 1959–1966 and officially named in 1967, after the late American glaciologist Fredrik T. Thwaites. The glacier flows into Pine Island Bay, part of the Amundsen Sea, at surface speeds which exceed 2 kilometres (1.2 mi) per year near its grounding line. Its fastest-flowing grounded ice is centered between 50 and 100 kilometres east of Mount Murphy. Like many other parts of the cryosphere, it has been adversely affected by climate change, and provides one of the more notable examples of the retreat of glaciers since 1850.
Ice calving, also known as glacier calving or iceberg calving, is the breaking of ice chunks from the edge of a glacier. It is a form of ice ablation or ice disruption. It is the sudden release and breaking away of a mass of ice from a glacier, iceberg, ice front, ice shelf, or crevasse. The ice that breaks away can be classified as an iceberg, but may also be a growler, bergy bit, or a crevasse wall breakaway.
Wilkins Sound is a seaway in Antarctica that is largely occupied by the Wilkins Ice Shelf. It is located on the southwest side of the Antarctic Peninsula between the concave western coastline of Alexander Island and the shores of Charcot Island and Latady Island farther to the west.
The Riiser-Larsen Sea is one of the marginal seas located in the Southern Ocean off East Antarctica and south of the Indian Ocean. It is delimited Astrid Ridge in the west and the Gunnerus Ridge and the Kainanmaru Bank in the east. It is bordered by the Lazarev Sea to the west and the Cosmonauts Sea to the east, or between 14°E and 30°E. Its northern border is defined to be the 65th parallel south. The name, proposed by the Soviet Union, was never officially approved by the International Hydrographic Organization (IHO).
A-38 was a large iceberg that split from the Filchner-Ronne Ice Shelf in Antarctica in October 1998. Soon after formation it split into two pieces, A-38A and A-38B, which drifted westwards on the Weddell Gyre. The icebergs moved north along the Antarctic Peninsula and reached its tip in February 2003. A-38A and A-38B increased speed in open sea and grounded in shallower waters to the east of South Georgia Island in December 2003. A-38A broke up into three pieces in March 2004 and drifted north where it decayed. A-38B split into two in April, with the eastern portion, now known as A-38G, drifting north and west to decay. The remainder of A-38B remained grounded, interfering with the foraging routes of seals and penguins in South Georgia, resulting in the deaths of their young. On 20 August 2004, A38-B broke into two, with the new portion drifting north and breaking up. The remainder of A-38B continued to break up through September 2004 and had completely decayed by 2005.
Adrian J. Luckman is a British glaciologist and professor of geography at Swansea University in Wales. He is a lead researcher for Project Midas, which monitored the Larsen C iceberg and the Larsen Ice Shelf.
The Weddell Sea Expedition 2019 was a 49 day expedition to the Weddell Sea, in Antarctica, that sought to study the glaciology and biology at and near the Larsen C ice shelf. It was the first expedition to investigate the area that Iceberg A-68 broke away from in July 2017.
Iceberg A-74 is an iceberg that calved from the north side of the Antarctic Brunt Ice Shelf in February 2021. Its calving had been anticipated due to large ice rifts that opened up in September 2019 and spread in the Antarctic summer of 2020–21. The iceberg measured 1,270 square kilometres (490 sq mi) soon after calving. It has moved away from the Antarctic coast which allowed, on 13–14 March 2021, the research vessel Polarstern to complete a circumnavigation as part of a research expedition. The Polarstern has photographed the sea bed which has provided an insight into fauna that can survive up to 30 kilometres (19 mi) from the nearest daylight.
In mid-May 2021, A-76 was, before it broke into three, the world's largest floating iceberg, calved from the Filchner–Ronne Ice Shelf in Antarctica.
A23a is a large tabular iceberg which calved from the Filchner–Ronne Ice Shelf in 1986. It was stuck on the sea bed for many years but then started moving in 2020. Its area is about 3,900 square kilometres (1,500 sq mi), which made it one of the largest icebergs in the world until it was temporarily surpassed in size by A-76.
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