Larsen Ice Shelf

Approaching the Larsen Ice Shelf

Larsen Ice Shelves A, B, C, and D

The Larsen Ice Shelf is a long, fringing ice shelf in the northwest part of the Weddell Sea, extending along the east coast of the Antarctic Peninsula in the British Antarctic Territory from Cape Longing to the area just southward of Hearst Island.

The ice shelf is named for Captain Carl Anton Larsen, the founder of South Georgia's industry, whaling. As the master of the Norwegian whaling vessel Jason, he sailed along the ice front as far as 68°10' South during December 1893, and is reckoned to be the first man to ski in Antarctica, when he took to skis on the ice shelf.

In finer detail, the Larsen Ice Shelf is a series of shelves that occupy (or occupied) distinct embayments along the coast. Researchers who work in the area name the segments from north to south:

• Larsen A (the smallest);
• Larsen B;
• Larsen C (the largest);
• Larsen D further south; and
• Larsen E, F and G, smaller sections, are also named.

The breakup of the ice shelf since the mid-1990s has been widely reported, with the collapse of Larsen B in 2002 being particularly dramatic. A large section of the Larsen C shelf was reported to have broken away in the week beginning 10 July 2017.

Carl Anton Larsen

The dynamic ice shelf

The collapse of Larsen B has revealed a thriving chemotrophic ecosystem half a mile below the sea. The discovery was accidental. U.S. Antarctic Program scientists were in the north-western Weddell Sea investigating the sediment record in a deep, vast glacial trough. Methane and hydrogen sulphide associated with cold seeps is suspected as the source of the chemical energy powering the ecosystem. The area had been protected by the overlying ice sheet from debris and sediment which was seen to be building up on the white microbial mats after the breakup of the ice sheet. The clams were observed clustered about the vents.

Studies show that the former Larsen A region, which was the furthest north and was just outside the Antarctic Circle, had previously broken up in the middle of the present interglacial and reformed only about 4,000 years ago. The former Larsen B, by contrast, had been stable for at least 10,000 years. The ice of the shelf is renewed on a much shorter time-scale and the maximal ice age on the current shelf dates from only two hundred years ago. The speed of Crane Glacier increased threefold after the collapse of the Larsen B and this is likely to be due to the removal of a buttressing effect of the ice shelf. Data collected in 2007 by an international team of investigators through satellite-based radar measurements suggests that the overall ice-sheet mass balance in Antarctica is increasingly negative.

Breakup

The Larsen disintegration events were unusual by past standards. Typically, ice shelves lose mass by iceberg calving and by melting at their upper and lower surfaces. According to a paper published in Journal of Climate in 2006, the peninsula at Faraday station warmed by 2.94 °C from 1951 to 2004, much faster than Antarctica as a whole and faster than the global trend, through a strengthening of the winds circling the Antarctic. Once the disintegration of all three of Larsen A, B and C has completed, the enormous Larsen Ice Shelf viewed in 1893 by Carl Anton Larsen and his crew aboard the Jason would largely be gone - less than a century and a half after its discovery.

Larsen A

The Larsen A ice shelf disintegrated in January 1995.

Larsen B

The collapse of Larsen B, showing the diminishing extent of the shelf from 1998 to 2002

From 31 January 2002 to March 2002 the Larsen B sector partially collapsed and parts broke up, 1,255 square miles (3,250 km²) of ice 720 feet thick. In 2015 a study concluded that the remaining Larsen B ice-shelf will disintegrate by the end of the decade, based on observations of faster flow and rapid thinning of glaciers in the area.

Larsen B was stable for at least 10,000 years, essentially the entire Holocene period since the last glacial period, according to researchers at Queen's University, Toronto. By contrast, Larsen A "was absent for a significant part of that period and reformed beginning about 4,000 years ago," according to the study.

Despite its great age, the Larsen B was affected by alterations in climate which caused warm currents to eat away the underside of the shelf. What especially surprised glaciologists was the speed of the breakup, which was a mere three weeks (or less). Factors they had not anticipated were the powerful effects of liquid water; ponds of meltwater formed on the surface during the near 24 hours of daylight in the summertime, then the water flowed down into cracks and, acting like a multitude of wedges, levered the shelf apart.

Andrew Fleming (remote sensing manager at the British Antarctic Survey) said to Reuters: "The Larsen B shattered like car safety glass into thousands and thousands of pieces. It disappeared in the space of about a week."

Larsen C

2016 rift in Larsen C, wide view

Larsen C is the fourth largest ice shelf in Antarctica, with an area, since July 2017, of about 17,000 square miles.

In 2004, a report concluded that although the remaining Larsen C region appeared to be relatively stable, continued warming could lead to its breakup within the following decade.

News reports in the summer of 2016 suggested that this process had begun. On 10 November 2016 scientists photographed the growing rift running along the Larsen C ice shelf, showing it running about 70 miles long with a width of more than 100 yards, and a depth of 550 yards. By December 2016, the rift had extended another 13 miles to the point where only 12 miles of unbroken ice remained and calving was considered to be a certainty in 2017. This was predicted to cause the collapse of between nine and twelve percent of the ice shelf, 2,300 square miles. The calved fragment was predicted to be 1,150 feet thick and to have an area of about 1,900.00 square miles (0.24 the size of Wales). If the calved iceberg does not break into pieces, it would be among the largest icebergs ever recorded.

On 12 July 2017, Project MIDAS announced that a large, 2,200 square-mile portion of Larsen C had broken from the mainland at some point between 10 and 12 July. The iceberg weighs more than a trillion tons and is more than 650 feet thick. The iceberg is not expected to be an immediate danger to shipping, but it could pose a threat if it moves significantly northwards.

Larsen D

The Larsen D Ice Shelf is located between Smith Peninsula in the south and Gipps Ice Rise in the north. It is considered to be generally stable. Over roughly the past fifty years it has advanced where the other ice shelves, the George VI, Bach, Stange, and Larsen C shelves have all retreated. However, this gain has been relatively small in comparison to the retreat of the others. The most recent survey of Larsen D measured it at Error: mismatched units. There is fast ice along the entire front. This makes it difficult to interpret the ice front because the semi-permanent sea ice varies in thickness and may be nearly indistinguishable from shelf ice.

Gallery

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  Clear view of the Antarctic Peninsula, the Larsen Ice Shelf, and the sea ice covered waters around the region.

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  Larsen B area in March 2013

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  2016 rift in Larsen C, detail

Outside links

("Wikimedia Commons" has material about Larsen Ice Shelf)

• Location map: 67°30’0"S, 62°30’0"W
• "Break up of the Larsen Ice Shelf, Antarctica", NASA Earth Observatory.
• Coastal-change and Glaciological Map of the Larsen Ice Shelf Area, Antarctica, 1940-2005 United States Geological Survey
• Antarctic ice rift close to calving, after growing 17km in 6 days (Swansea University, Project Midas - June 2017)