The Ross Ice Shelf is the largest expanse of floating ice on the planet (similar to the size of France). Because of this, it acts as a buttress, holding back the Antarctic glaciers, preventing them from flowing into the ocean. If destabilised – either by the warming ocean below or the warming atmosphere above – this vital role could be diminished, resulting in a rapid rise in sea levels.
Monitoring the ice shelf is therefore essential and scientists from the American Geophysical Union, suported by the Office of Polar Programs for the US National Science Foundation, have discovered a new tool with which to do so. In 2014, the team buried 34 super-sensitive seismic sensors beneath the ice shelf’s surface, a terrain made up of a thick blanket of snow several metres deep and rippled by massive dunes. The instruments measured seismic signals – the waves of energy produced by movement within the earth. The data revealed that winds whipping across the snow dunes cause the ice shelf’s surface to vibrate. This steady vibration results in the emission of seismic ‘tones’. When processed at a frequency audible to humans, these tones sound like an eerie, warbling hum, a continuous song that would not sound out of place in a sci-fi movie.
Rick Aster, professor of geophysics at Colorado State University and a member of the team, explains that the tones provide an extremely accurate way of monitoring the ice. This is because when weather conditions change, the pitch of the hum responds. ‘A remarkable thing we discovered during this study was that even during a relatively subtle warming event that only produced a tiny bit of melt on the ice shelf, we could see very strong indications in this signal,’ he says. ‘It enables us to monitor the temperature and the melting of the surface of an ice shelf on a minute-by-minute basis.’
The team are now considering burying the sensors deeper under the ice to monitor vibration at various depths. ‘The first thing to do is to understand the processes and the changes that are happening,’ says Aster. ‘Over 90 per cent of the world’s ice is in Antarctica. As it melts it contributes a greater and greater proportion to rising sea levels and that’s felt all around the world.’
This was published in the January 2019 edition of Geographical magazine
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