With a hat-tip to GeoffBeacon, the linked reference indicates that repeated drainage of surface meltwater likely formed a massive subsurface ice layer within the Larsen C Ice Shelf; which raises concerns not only about the fragility of the Larsen C Ice Shelf, but also of future fragility of other Antarctic ice shelves
Bryn Hubbard, Adrian Luckman, David W. Ashmore, Suzanne Bevan, Bernd Kulessa, Peter Kuipers Munneke, Morgane Philippe, Daniela Jansen, Adam Booth, Heidi Sevestre, Jean-Louis Tison, Martin O’Leary & Ian Rutt (2016), "Massive subsurface ice formed by refreezing of ice-shelf melt ponds", Nature Communications, Volume: 7, Article number: 11897, doi:10.1038/ncomms11897
http://www.nature.com/ncomms/2016/160610/ncomms11897/full/ncomms11897.htmlAbstract: "Surface melt ponds form intermittently on several Antarctic ice shelves. Although implicated in ice-shelf break up, the consequences of such ponding for ice formation and ice-shelf structure have not been evaluated. Here we report the discovery of a massive subsurface ice layer, at least 16 km across, several kilometres long and tens of metres deep, located in an area of intense melting and intermittent ponding on Larsen C Ice Shelf, Antarctica. We combine borehole optical televiewer logging and radar measurements with remote sensing and firn modelling to investigate the layer, found to be ~10 °C warmer and ~170 kg m−3 denser than anticipated in the absence of ponding and hitherto used in models of ice-shelf fracture and flow. Surface ponding and ice layers such as the one we report are likely to form on a wider range of Antarctic ice shelves in response to climatic warming in forthcoming decades."
See also (& the associated image):
http://www.carbonbrief.org/discovery-exposes-fragility-of-antarcticas-larsen-c-ice-shelfExtract: "Meltponds tend to form in a line “like a string of sausages” and are thought to have contributed to the collapse of ice shelves in the past, including Larsen B.
...
Until now, scientists had suspected that meltponds exerted stress through the sheer weight of the water pushing down on the ice below it. But Hubbard and his team wondered if there was a different explanation. He tells Carbon Brief:
“The rationale for our project was to investigate whether the ponds had an influence on the internal structure of the underlying ice shelf.”
...
The team drilled a 100m-long borehole in a part of the Larsen-C ice shelf called Cabinet Inlet, where scientists first spotted meltponds 15 years ago.
Just a few metres below the surface, they struck upon a layer of solid ice about 100 metres thick, formed as water from the meltponds percolates through the ice and refreezes.
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The vast icy layer below Larsen C is a concern, says Hubbard. It is warmer than the compacted snow it replaced because of the latent heat that is released as the percolating meltwater refreezes at depth. Thi, in turn affects how the ice moves, Hubbard explains:
“Similar to syrup, warm ice flows more readily than cold ice.”
Hubbard and his team installed a string of instruments to take measurements within the icy layer, returning to collect the data a year later. They found temperatures of between -5C and -10C, a full 10C above what they expected for this depth range. Hubbard says:
“This suggests that not only is the massive ice layer denser than that which would be present in the absence of surface ponds, but that it is also substantially warmer, both having implications for the movement and stability of the ice shelf.”"