Ice shelf collapses
Ice shelf collapses refer to the disintegration of floating extensions of continental ice sheets, primarily found along the coast of Antarctica. These ice shelves play a crucial role in stabilizing the glaciers that feed into them by acting as buttresses, slowing their flow into the ocean. The largest ice shelves, such as the Ross and Ronne-Filchner, account for a significant portion of the Antarctic ice mass. Ice shelves gain mass through ice flow from land, snow accumulation, and seawater freezing, but they primarily lose mass through iceberg calving and melting caused by warmer ocean waters.
Recent observations indicate that ice shelves, particularly in the West Antarctic Peninsula, have been shrinking over the past few decades, with notable events such as the collapse of Larsen B in 2002. While the complete melting of these shelves may not significantly raise sea levels, it could lead to accelerated glacier flow and contribute to sea level rise if the ice shelves destabilize. Interestingly, ice shelves in certain regions of Antarctica, like the southern West Antarctic and East Antarctic ice sheets, remain relatively unaffected by climate change, suggesting a complex interplay of environmental factors influencing their stability.
Ice shelf collapses
The debate over global warming has prompted a renewed interest in the study of ice shelves, particularly after the collapse of the Larsen A and Larsen B shelves in 1995 and 2002, respectively. These collapses have been seen not only as products of global warming, but also as part of a process by which the movement of Antarctic ice toward the ocean has been accelerated.
Background
Ice shelves are the seaward extensions of continental ice sheets. They are found extending from 50 percent of the coast of Antarctica and account for 11 percent of the mass of ice of the Antarctic Ice Sheets. The two largest ice shelves—Ross (472,960 square kilometers) and Ronne-Filchner (422,420 square kilometers)—together represent 67 percent of the total area of Antarctic ice shelves. Ice shelves are typically thinner at their seaward edge; the largest shelves reach a depth of 1,300 meters near the grounding line (the location where the ice begins to float), but thin to 200 meters at the leading edge.
Formation of Ice Shelves
Ice shelves gain mass in three different ways. The primary source is the ice sheet that moves off the land surface onto the water, but accumulated snow on their upper surface and the freezing of seawater to the lower one also contribute. On the other hand, ice shelves lose mass in five ways: by of icebergs, by the melting of ice in contact with the sea, by snow blowing off the edge of ice shelves, by enhanced of ice under the very strong Antarctic winds, and by superficial melting. Since surface melting in Antarctica is negligible, and since wind ablation is limited in general, nearly all mass loss is the result of either iceberg calving at the seaward margin or bottom melting of ice in contact with the sea.
Ice Shelves of the West Antarctic Peninsula
With the widespread availability of video clips on the Internet, many people have observed the breaking of very large tabular icebergs off the Antarctic Peninsula. The calving of icebergs is a natural phenomenon that occurs regularly under normal climatic conditions. This calving should not be interpreted as a sure sign of global warming. In the extreme north of the Antarctic Peninsula, ice shelves are called Larsen A, B, C, and D, named in sequence from north to south. The Larsen A began to retreat at a very rapid pace in January 1995. The breakup of Larsen A was irrefutably a response to the rise in ocean temperature. South of Larsen A, Larsen B calved large tabular icebergs beginning in 1995, prior to a larger disintegration that occurred in the first three months of 2002. In 2008, the Wilkins Ice Shelf that had broken up in 1998 partially disintegrated. The culprit seemed to be the presence of warm ocean waters melting ice shelves from beneath and destabilizing the ice shelf at the grounding line.
According to climate estimates in the 2020s, even if world governments meet many of their most ambitious climate goals, significant increases in the melting rate of the West Antarctic ice sheets was inevitable. They found that reducing emissions would likely have a positive effect on the ice sheets following the year 2100. However, prior to that, melting would continue to increase from the effects of previous centuries' greenhouse gas emissions.
Ice Shelves as Buttresses
Because ice shelves may be very thick, they are often anchored on the continental shelf, where they begin to float. The grounding of these ice shelves allows them to slow down the outward movement of ice sheets by acting as a buttress if they are thick enough. This effect is lost if the ice shelf disintegrates. In the case of the Larsen B Ice Shelf, its disintegration in 2002 led to an acceleration of the outward flow of ice from the glacier that feeds it.
Context
Although there is no doubt that ice shelves in the West Antarctic Peninsula have decreased in size over the last three decades, their complete melting would not raise sea level by more than a few millimeters. Their destruction could, however, contribute significantly to rising sea level if the glaciers feeding these ice shelves were to speed up once the ice shelf stops being grounded. A study published in Nature Communications in 2024 indicated that glaciers were melting much faster than in the past, about five times faster from 2015 to 2019 than from 1948 to 1979.
Key Concepts
- glacier: a mass of ice that flows downhill, usually within the confines of a former stream valley
- ice sheets: masses of ice covering large areas of land
- ice shelf: a platform of freshwater ice floating over the ocean
- West Antarctic ice sheet: the smallest ice sheet in Antarctica, located west of the Transantarctic Mountains
Bibliography
Copeland, Sebastian. The Global Warning. San Rafael, Calif.: Earth Aware Editions, 2007.
Davies, Bethan. "Accelerating Glacier Volume Loss on Juneau Icefield Driven by Hypsometry and Melt-Accelerating Feedbacks." Nature Communications, vol. 15, no. 5099, 2 July 2024, doi.org/10.1038/s41467-024-49269-y. Accessed 21 Dec. 2024.
McGonigal, David. Antarctica: Secrets of the Southern Continent. Richmond Hill, Ont.: Firefly Books, 2008.
"Melting of Alaskan Glaciers Accelerating Faster Than Previously Thought." University of Leeds, 3 July 2024, www.leeds.ac.uk/news-environment/news/article/5601/melting-of-alaska-glaciers-accelerating-faster-than-previously-thought. Accessed 21 Dec. 2024.
Roberts, Lily. "Increase in West Antarctic Ice Sheet Melting Inevitable in the 21st Century." Columbia Climate School, 26 Jan. 2024, news.climate.columbia.edu/2024/01/26/increase-in-west-antarctic-ice-sheet-melting-inevitable-in-21st-century/. Accessed 21 Dec. 2024.
Trewby, Mary. Antarctica: An Encyclopedia from Abbott Ice Shelf to Zooplankton. Toronto: Firefly Books, 2002.
Turney, Chris. Ice, Mud, and Blood: Lessons from Climates Past. New York: Macmillan, 2008.