Larsen Ice Shelf
Encyclopedia
The Larsen Ice Shelf is a long, fringing ice shelf
in the northwest part of the Weddell Sea
, extending along the east coast of Antarctic Peninsula
from Cape Longing
to the area just southward of Hearst Island
. Named for 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 three shelves that occupy (or occupied) distinct embayments along the coast. From north to south, the three segments are called Larsen A (the smallest), Larsen B, and Larsen C (the largest) by researchers who work in the area. The Larsen A ice shelf disintegrated in January 1995. The Larsen B ice shelf disintegrated in February 2002. The Larsen C ice shelf appears to be stable for the time being, though scientists predict that, if localized warming continues at its current rate, the shelf could disintegrate at some point within the foreseeable future.
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. The disintegration events are linked to the ongoing climate warming in the Antarctic Peninsula
, about 0.5 °C per decade since the late 1940s, which is a consequence of localized warming of the Antarctic peninsula. This localized warming is caused by anthropogenic global warming
, according to some scientists through strengthening of the Antarctic annular winds.
collapsed in a single season. Larsen B was stable for up to 12,000 years, essentially the entire Holocene
period since the last glacial period, according to Queen's University
researchers. 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 clearly in trouble at the time of the collapse. With warm currents eating away the underside of the shelf, it had become a "hotspot of global warming." What especially surprised glaciologists was the speed of the breakup, which was a mere three weeks (or less). A factor they had not anticipated was 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, almost in one fell swoop. Global increase in air temperature was not the only factor contributing to the break according to Ted Scambos, of the University of Colorado
's national snow and ice data centre.
Although the remaining Larsen C region, which is the furthest south, appears to be relatively stable for now, continued warming could lead to its breakup within the next decade. If disintegration should occur with this last major sector, which is larger in size than the US states of New Hampshire and Vermont combined—then the enormous Larsen Ice Shelf viewed in 1893 by Carl Anton Larsen and his crew aboard the Jason will largely be gone in just over a century after its discovery.
The collapse of Larsen B has revealed a thriving ecosystem
800 m (half a mile) below the sea. "Despite near freezing and sunless conditions, a community of clams and a thin layer of bacterial mats are flourishing in undersea sediment
s. [...] The discovery was accidental. U.S. Antarctic Program scientist
s were in the northwestern Weddell Sea investigating the sediment record in a deep glacial trough twice the size of [the US state of] Texas
."
Studies show that in the middle of the present interglacial
the former Larsen A region, which was the furthest north and outside the Antarctic Circle, had previously broken up and reformed only about 4,000 years ago, although the former Larsen B had been stable for at least 10,000 years. 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. Recent data collected by an international team of investigators through satellite-based radar measurements suggests that the overall ice-sheet mass balance in Antarctica is increasingly negative.
Ice shelf
An ice shelf is a thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Greenland and Canada. The boundary between the floating ice shelf and the grounded ice that feeds it is called...
in the northwest part of the Weddell Sea
Weddell Sea
The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha Coast, Queen Maud Land. To the east of Cape Norvegia is...
, extending along the east coast of Antarctic Peninsula
Antarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
from Cape Longing
Cape Longing
Cape Longing is a rocky cape on the east coast of Graham Land, forming the south end of a large ice-covered promontory which marks the west side of the south entrance to Prince Gustav Channel...
to the area just southward of Hearst Island
Hearst Island
Hearst Island is an ice-covered, dome-shaped island lying east of Cape Rymill, in the Weddell Sea, off the eastern coast of Palmer Land. The island is long, in a North-South direction, wide, and rises to ....
. Named for Captain Carl Anton Larsen
Carl Anton Larsen
Carl Anton Larsen was a Norwegian Antarctic Explorer, who made important contributions to the exploration of Antarctica, the most significant being the first discovery of fossils, for which he received the Back Grant from the Royal Geographical Society...
, the master of the Norwegian whaling vessel Jason
Jason (Ship)
Jason was a Norwegian whaling vessel laid down in 1881 in Rødsverven, Norway, the same shipyard which later built Ernest Shackleton's ship the Endurance...
, 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 three shelves that occupy (or occupied) distinct embayments along the coast. From north to south, the three segments are called Larsen A (the smallest), Larsen B, and Larsen C (the largest) by researchers who work in the area. The Larsen A ice shelf disintegrated in January 1995. The Larsen B ice shelf disintegrated in February 2002. The Larsen C ice shelf appears to be stable for the time being, though scientists predict that, if localized warming continues at its current rate, the shelf could disintegrate at some point within the foreseeable future.
The Larsen disintegration events were unusual by past standards. Typically, ice shelves lose mass by iceberg
Iceberg
An iceberg is a large piece of ice from freshwater that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice...
calving
Ice calving
Ice calving, also known as glacier calving or iceberg calving, 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...
and by melting at their upper and lower surfaces. The disintegration events are linked to the ongoing climate warming in the Antarctic Peninsula
Antarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
, about 0.5 °C per decade since the late 1940s, which is a consequence of localized warming of the Antarctic peninsula. This localized warming is caused by anthropogenic global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
, according to some scientists through strengthening of the Antarctic annular winds.
Breakup
During 31 January 2002–7 March 2002 the Larsen B sector collapsed and broke up, 3,250 km² of ice 220 m thick disintegrated, meaning an ice shelf covering an area comparable in size to the US state of Rhode IslandRhode Island
The state of Rhode Island and Providence Plantations, more commonly referred to as Rhode Island , is a state in the New England region of the United States. It is the smallest U.S. state by area...
collapsed in a single season. Larsen B was stable for up to 12,000 years, essentially the entire Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
period since the last glacial period, according to Queen's University
Queen's University
Queen's University, , is a public research university located in Kingston, Ontario, Canada. Founded on 16 October 1841, the university pre-dates the founding of Canada by 26 years. Queen's holds more more than of land throughout Ontario as well as Herstmonceux Castle in East Sussex, England...
researchers. 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 clearly in trouble at the time of the collapse. With warm currents eating away the underside of the shelf, it had become a "hotspot of global warming." What especially surprised glaciologists was the speed of the breakup, which was a mere three weeks (or less). A factor they had not anticipated was 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, almost in one fell swoop. Global increase in air temperature was not the only factor contributing to the break according to Ted Scambos, of the University of Colorado
University of Colorado at Boulder
The University of Colorado Boulder is a public research university located in Boulder, Colorado...
's national snow and ice data centre.
Although the remaining Larsen C region, which is the furthest south, appears to be relatively stable for now, continued warming could lead to its breakup within the next decade. If disintegration should occur with this last major sector, which is larger in size than the US states of New Hampshire and Vermont combined—then the enormous Larsen Ice Shelf viewed in 1893 by Carl Anton Larsen and his crew aboard the Jason will largely be gone in just over a century after its discovery.
The collapse of Larsen B has revealed a thriving ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
800 m (half a mile) below the sea. "Despite near freezing and sunless conditions, a community of clams and a thin layer of bacterial mats are flourishing in undersea sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s. [...] The discovery was accidental. U.S. Antarctic Program scientist
Scientist
A scientist in a broad sense is one engaging in a systematic activity to acquire knowledge. In a more restricted sense, a scientist is an individual who uses the scientific method. The person may be an expert in one or more areas of science. This article focuses on the more restricted use of the word...
s were in the northwestern Weddell Sea investigating the sediment record in a deep glacial trough twice the size of [the US state of] Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
."
Studies show that in the middle of the present interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...
the former Larsen A region, which was the furthest north and outside the Antarctic Circle, had previously broken up and reformed only about 4,000 years ago, although the former Larsen B had been stable for at least 10,000 years. The maximal ice age on the current shelf dates from only two hundred years ago. The speed of Crane Glacier
Crane Glacier
Crane Glacier , is a narrow glacier which flows 30 miles in an east-northeasterly direction through a deep trough into Exasperation Inlet, on the east coast of Antarctic Peninsula. Sir Hubert Wilkins photographed this feature from the air in 1928 and gave it the name Crane Channel, after C.K...
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. Recent data collected by an international team of investigators through satellite-based radar measurements suggests that the overall ice-sheet mass balance in Antarctica is increasingly negative.