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Scientists who have witnessed Antarctic ice shelf decay are escalating concerns that rising air temperatures will push these frozen masses to unprecedented fractures.
The effect of meltwater on ice shelves has long been discussed by glaciologists. Increased global temperatures due to unprecedented carbon emissions from human activity cause ice to thaw. This can lead to water pooling on the ice surface. This in turn strains the structure below, causing it to buckle and, potentially, split apart.
Rising sea levels
Fractured ice shelves are a critical threat to rising sea levels. While sea ice forms from cold oceans during the southern hemisphere winter, their meltdown in warmer months makes only a minor change to sea levels.
But large ice sheets, shelves and glaciers fixed to the Antarctic landmass pose a far larger threat. At the extreme, melting all of Earth’s ice sheets and glaciers would raise sea levels by at least 60m.
The breakdown of George VI
in 2019, a team of UK and US researchers travelled to the George VI Ice Shelf and identified a region they believed would be susceptible to future meltwater pools.
There, they set up time-lapse cameras, water pressure and GPS sensors to monitor changes in the depression along the ice surface. With the GPS sensors measuring fluctuations in ice elevation, water pressure sensors monitoring the depth of the lake and cameras snapping images of the region every 30 minutes, they saw what happened to the ice shelf as that new meltwater pool formed.
That pool formed during a then-record season for Antarctic ice melt and sea ice decline. When the group returned to study their data after the emergence of the COVID-19 pandemic, they found that the water caused the ice beneath the centre of the pool to buckle around 30cm.
A breakthrough in meltwater knowledge
And this process repeats as the pool drains through tiny cracks in the basin ice, with the repetitive flexing causing the depression to widen by about 30cm.
The study, led by glaciologist Alison Banwell from the Cooperative Institute for Research In Environmental Sciences at the University of Colorado Boulder, could help explain ice shelf collapses like the sudden split of the Larsen B Ice Shelf in 2002.
That event was marked by the emergence of meltwater lakes on top of the shelf’s surface ice.
‘Scientists have predicted and modelled that surface meltwater loading could cause ice shelves to fracture, but no one had observed the process in the field, until now,’ says Banwell.
‘We believe these types of circular fractures were key in the chain reaction style lake drainage process that helped to break up the Larsen B Ice Shelf.
‘These observations are important because they can be used to improve models to better predict which Antarctic ice shelves are more vulnerable and most susceptible to collapse in the future.’
The research is published in the Journal of Glaciology.
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