Posted for Quirin Schiermeier
If an ice shelf breaks up and no one alerts the media, has anything really happened?
The British Antarctic Survey has released photos showing that a sizable part of the Wilkins ice shelf off the Antarctic peninsula is currently “hanging by a thread”, supported by a thin strip of ice between two islands (press release, news coverage from BBC, VoA, Reuters, blogs).
However a massive chunk of 400 square kilometres has already broken off the same shelf, says Matthias Braun, a remote sensing expert at the University of Bonn.
Last July Braun saw the first evidence for a large crack in the Wilkins ice shelf in images from the Japanese ALOS sensor. A big chunk of ice started to break away on February 28, at the end of the Antarctic summer.
As shelf ice is floating on the ocean, its melting has no immediate effect on sea level height. However, loss of shelf ice allows Antarctica’s huge glaciers to flow faster towards the coast and any acceleration of glacier flow does contribute to sea level rise. The destabilization of the Wilkins ice shelf adds to such concerns.
“We can see clearly see on satellite images that the recent break-up has resulted in lengthening and coalescence of older existing cracks and failure zones,” says Angelika Humbert, an ice dynamics modeller at the University of Münster in Germany. “This is a major threat for the stability of the whole ice shelf.”
Several large ice shelfs on the Antarctic Peninsula are in a precarious state, or have begun to crumble away.
Sudden break-ups, such as the collapse of the Larsen-B ice shelf between January and March of 2003, are triggered by excessive internal tensions and hydrostatic forces, but scientists assume that climate change may play a major role in the processes that lead to disintegration.
The Antarctic Peninsula is a known hot-spot of global warming, with mean temperatures having increased there by around 3 degrees Celsius over the last 50 years.
It is likely, although hard to measure, that ice shelfs around the Peninsula are massively losing mass at the bottom as the ocean gets warmer. However, they may gain mass at the surface as a result of more snowfall. How the two trends balance out is unclear.
But researchers do suspect that the mechanical properties of shelf ice might change in ways that favour its disintegration. What’s more, says Humbert, the mean surface temperature of shelf ice in the region is getting is close to a value beyond which wide-spread destabilization might become inevitable.
Photo: Wilkins Ice Shelf from BAS Twin Otter / BAS