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Giant icebergs have been breaking off the edge of Pine Island ice shelf<\/p>\n
NASA\/Brooke Medley<\/p>\n<\/p>\n
A large and fast-melting glacier in West Antarctica has sped up dramatically since 2017. This may be a sign that the floating ice shelf in front of it is no longer helping to hold back the ice.<\/p>\n
Pine Island glacier is the fastest-flowing glacier in Antarctica and the largest contributor to sea-level rise of all Antarctic glaciers. It is a key part of the West Antarctic ice sheet, which holds enough ice to raise the global sea level by 5.3 metres if melted completely.<\/p>\n
The Pine Island ice shelf lies in front of the glacier and juts out over the ocean. It is thought to play a crucial role in holding back the inland ice and shielding it from warm water, buttressing an amount of ice equivalent to 51 centimetres of sea-level rise.<\/p>\n
The instability of Pine Island glacier<\/a> and the neighbouring Thwaites glacier, nicknamed the Doomsday glacier, poses a major threat to the long-term viability of the broader West Antarctic ice sheet.<\/p>\n Sarah Wells-Moran<\/a> at the University of Chicago and her colleagues tracked the movement of Pine Island glacier using imagery from the Copernicus Sentinel-1 Satellite and observations going back to the early 1970s.<\/p>\n The glacier\u2019s velocity increased from 2.2 kilometres per year in 1974 to 4 kilometres per year by 2008. Then, between 2017 and 2023, it jumped to nearly 5 kilometres per year, a 20 per cent increase over six years and a 113 per cent increase since 1973.<\/p>\n Between 1973 and 2013, the rate of ice discharge from Pine Island glacier increased by more than three-quarters.<\/p>\n These changes led to a dramatic retreat of the glacier\u2019s grounding line, the point at which the ice shelf begins to float rather than rest on the seafloor, by more than 30 kilometres.<\/p>\n The team compared these observations with computer models and concluded that the rapid acceleration has occurred due to the thinning and fracturing of the ice shelf as warmer sea water reaches further along its underside. The sides of the ice shelf have become detached from the surrounding ice, \u201cunzipping\u201d the margins of the shelf, write Wells-Moran and her colleagues.<\/p>\n They conclude that Pine Island ice shelf \u201cnow provides negligible buttressing to the ice upstream\u201d, which has accelerated the loss of ice from West Antarctica.<\/p>\n Sue Cook<\/a> at the University of Tasmania in Australia says calving \u2013 the break-up of ice at the front of the ice shelf \u2013 isn\u2019t enough to explain the glacier\u2019s acceleration. \u201cMost likely the cause is increased damage in the shear margins of the glacier,\u201d she says. \u201cThis study helps to confirm that mechanism.\u201d<\/p>\n
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