Antarctica is fringed with floating ice shelves. They are floating extensions of the Antarctic Peninsula ice sheet, and can be very large indeed. The Ross Ice Shelf is the size of France - see the map below. However, in recent years, the dramatic and rapid loss of ice shelves fringing the Antarctic Peninsula have hit the news.
The Antarctic Peninsula is the third ice sheet on Antarctica. The West Antarctic Ice Sheet (WAIS) and East Antarctic Ice Sheet are the other two. The Antarctic Peninsula Ice Sheet (APIS) is of great interest because it is the most temperate of the three ice sheets, and contains up to 0.6 m sea level rise (in addition to the +1.0 m sea level rise predicted by the IPCC over the next 100 years).
The Antarctic Peninsula. Credit: USGS
The disintegration of the Antarctic Ice Shelves
The first ice shelf to dramatically disintegrate was the Larsen B ice shelf. Read about it in a British Antarctic Survey press release here. The Larsen B Ice Shelf began to collapse in 1995, and disintegrated over a matter of weeks. An armada of icebergs was dispatched into the Weddell Sea. More recently it appears that the Wilson Ice Shelf has begun to disintegrate. This has been accelerated by a 3C warming over the last 50 years; the Antarctic Peninsula is one of the most rapidly warming places on Earth.
The Impact of the Loss of the Ice Shelves
As ice shelves float at their specific density, their melting has no direct impact on sea level rise. You can test this yourself. Find yourself two water glasses. Put two 'ice bergs' (ice cubes) in one and fill it with water so that the ice cubes float. Mark the water level on the glass and note what happens when the ice melts - it will stay at the same level. With the second glass, put in four or five ice cubes and fill the glass so that most of the ice cubes are covered but they are not floating. When the ice melts, the water level in the glass will rise.
This is an important point to note. Melting ice shelves, like the floating ice cubes, will not cause the water level to rise. However, ice shelves are an important part of the glacial system, and strongly effect the ice dynamics within the continental ice sheet. With their loss, internal continental, non-floating ice speeds up, and calves more ice bergs into the ocean, rising sea level.
This works in the following manner. Ice shelves are pinned and grounded at certain points; they form in large bays and are constrained at their edges. They hold back the onshore fast-flowing ice streams. Ice streams are corridors of faster-flowing ice that is melted at its base. Ice streams drain the majority of the ice from ice caps, and contribute to the majority of ice dynamics. The ice streams are the same as the ice cubes that were not floating, and by adding more ice to the glass, the water level will rise.
Ice streams of the WAIS
Since the collapse of some of the ice shelves fringing the Antarctic Peninsula, outlet glaciers and ice streams in the vicinity have increased in speeds of up to 5 times, releasing large amounts of meltwater and ice bergs into the ocean. This of course is directly relevant to sea level rise. The role of sea ice is important as sea ice protects ice shelves from waves and storms, which can destabilise the ice shelf and aid its collapse.
The collapse of the ice shelves is one of the most visible aspects of modern climate change. It is very important to act now to curb global warming, to protect these fragile systems. Their destruction could result in real and rapid sea level rise, threatening our coastal towns, cities and wildlife habitats. With a large majority of the world's population living near the sea, we cannot afford to ignore this problem.
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