Sea ice reinforcing Antarctic ice sheet
Formed largely of freshwater glacial ice, the Larsen Ice Shelf is a series of three shelves occupying distinct embayments along the coast of the Antarctic Peninsula and are named A, B and C according to their location. Scientists from the British Antarctic Survey (BAS) identified sea ice forming along the bottom of Larsen C, the largest of the three, when their ten-year radar dataset from the ice shelf suggested that their equipment had failed. Based on previous experience of this scenario, combined with scientific modelling of sea-ice formation, they discovered that the places where the radar seemed to have stop working coincided with the parts of the shelf where ice could have formed from seawater.
‘The sea freezes at progressively cooler temperatures the deeper you go,’ said BAS oceanographer Dr Paul Holland, who led the study. ‘At the surface, seawater freezes at –2°C, but at a depth of one kilometre, it freezes at –3°C. So water at –2.5°C can exist in the deep sea beneath ice shelves, but freezes onto the base of the ice shelf if it rises.’
Sea ice behaves differently from glacier ice, which is normally at a temperature of –15°C and is quite brittle. The sea water freezing onto the bottom of Antarctic ice shelves is much warmer and is thought to be more pliable.
‘We think that’s partly why Larsen C isn’t breaking up,’ said Holland. ‘The marine ice just deforms, rather than breaks. This is obvious when you look at crevassing and iceberg calving in Larsen C – the marine ice is limiting both. It’s clear we need to consider the marine ice in predictions of when the ice shelf will eventually collapse.’
August 2009
‘The sea freezes at progressively cooler temperatures the deeper you go,’ said BAS oceanographer Dr Paul Holland, who led the study. ‘At the surface, seawater freezes at –2°C, but at a depth of one kilometre, it freezes at –3°C. So water at –2.5°C can exist in the deep sea beneath ice shelves, but freezes onto the base of the ice shelf if it rises.’
Sea ice behaves differently from glacier ice, which is normally at a temperature of –15°C and is quite brittle. The sea water freezing onto the bottom of Antarctic ice shelves is much warmer and is thought to be more pliable.
‘We think that’s partly why Larsen C isn’t breaking up,’ said Holland. ‘The marine ice just deforms, rather than breaks. This is obvious when you look at crevassing and iceberg calving in Larsen C – the marine ice is limiting both. It’s clear we need to consider the marine ice in predictions of when the ice shelf will eventually collapse.’
August 2009
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