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Ice loss in the Antarctic: Researchers find calving law

03/21/2012 - The ice of Antartica is in motion. Time and again, massive breaking off of icebergs has been observed – now scientists have for the first time presented a universal physical law for the large-scale disintegration of the ice-shelves. It describes how the speed of the ice plays an important role. The ice-shelves situated in the bays of the Antarctica, where the grounded ice is joined to ice on the ocean, are currently hindering a faster discharge of the ice masses. But the ice-shelves could abruptly change their state, the study by an international team of scientists shows. Big break-offs lead to a much faster discharge of inland ice into the ocean where it melts. Hence, the Antarctica could be contributing comparatively the fastest to global sea-level rise.
Ice loss in the Antarctic: Researchers find calving law

Satellite data shows that the break-off rate of icebergs from the Antarctic ice shelf increases with the spread of ice flow near the ice front (left). Orange colours represent the spread of ice flow, blue colours the contraction of the ice.

“In our study, the ice-shelves prove themselves as tipping-points within the earth system,” says Anders Levermann, lead author of the study. “Until now, it wasn’t clear that there can be different states. Our analysis shows that if too much ice breaks off at the ice-front, then there could possibly be nothing to retain it – the ice-front would continue to retreat further and further.” What happens within the sheet-shelf system is now described by the new equation developed by the scientists. The equation makes it possible to grasp the fundamental dynamics of the ice-shelves, according to Levermann, “although or precisely because it doesn’t include all details.”

This is not just of theoretical importance. A sudden retreat of, say, the Ross Ice Shelf to the smallest but still stable position would reduce the back stresses for the continental ice-sheet by more than 90%, application of the equation shows. “Thus, the so-called calving of shelves is a local event that might have global consequences,” says Levermann. “For now, it is a completely natural process – but as climate change proceeds, this process is going to change. Therefore, we need to understand it better.”

In simulations, the law proved its ability to calculate realistic fronts. Big break-offs, like the one of Larsen B ten years ago, were reproduced well by the equation. This shelf was stable for 12000 years. In Antarctica, a continent as big as Europe, enormous amounts of water are stored as ice. The surface of the ice ‑ in contrast to the Greenland ice-sheet, for example ‑ does not thaw due to the very cold temperatures. The ice thaws once it reaches the ocean – whose temperature will be influenced in the long-run by global warming.

 

Article: Levermann, A., Albrecht, T., Winkelmann, R., Martin, M.A., Haseloff, M., Joughin, I. (2012: Kinematic first-order calving law implies potential for abrupt ice-shelf retreat. The Cryosphere, 6, 273-286 [doi:10.5194/tc-6-273-2012]

 

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