Publication Date February 22, 2017 | Nature News & Comment

Giant crack in Antarctic ice shelf spotlights advances in glaciology

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...The speed at which glaciers connected to Larsen A and B flowed to the sea increased — by up to a factor of eight — after those ice shelves disintegrated, says Eric Rignot, a glaciologist at the University of California, Irvine. “Some of [the glaciers] have slowed down a little bit, but they are still flowing five times faster than before,” he notes. Khazendar and his colleagues have also found that two glaciers flowing into Larsen B started to accelerate before its collapse, as the ice shelf weakened.

 

..Larsen C, which covers 50,000 square kilometres with ice up to 350 metres thick

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The glaciers that flow into Larsen C contain enough water to raise the global sea level by about a centimetre — and they are likely to flow faster to the ocean in the absence of an ice shelf. In comparison, global sea levels are rising by about 3 millimetres a year, and a recent study estimated that one-third of that comes from ice loss in Antarctica and Greenland

Satellite images show that Larsen C has been receding since the 1980s, and radar measurements suggest that its ice is also thinning, Rignot says. Scientists have also seen meltwater ponds forming on the ice shelf’s surface 4; the same sort of ponds probably hastened the disintegration of Larsen B by carving holes in the ice and expanding cracks.

The ice sheet is protected, to some degree, from rapid collapse by favourable seafloor geometry. A pair of underwater ridges that surround Larsen C create friction that slows the flow of ice to the ocean.

Still, the parallels with the decline of Larsen B are striking, says Adrian Luckman, a glaciologist at Swansea University, UK, who heads a team that has monitored the Larsen C ice crack for several years. Larsen B experienced a major iceberg-calving event in 1995, followed by gradual retreat and then complete collapse seven years later. Larsen C may follow a similar pattern, he says, although it’s not clear how soon collapse might follow the imminent calving event.