The Greenland ice sheet has been hiding a secret. But how big a secret is only just becoming clear. Until recently, researchers had identified just four sub-glacial lakes beneath the sheet, which is approximately seven times the size of the UK and, in places, more than three kilometres thick. Now, a more thorough look at radar data of the region, collected by NASA, has revealed there to be at least 60 lakes lurking beneath.
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Sub-glacial lakes are bodies of meltwater which form beneath ice-masses. The meltwater might be derived from the pressure of the thick ice above, by heat generated from the flow of the ice, or from water on the surface draining to the bed. This water becomes trapped in depressions within the ice and forms lakes. ‘For a long time in Greenland it was thought that there weren’t any sub-glacial lakes because the drainage system is really efficient at getting water from the surface of the ice to the bed and then out to the ocean,’ explains Jade Bowling, lead author of the study from the University of Leicester. ‘People just didn’t think that water was stored there.’
In order to prove the doubters wrong, Bowling had to meticulously study more than 500,000km of airborne radio echo sounding data that provides images of the bed of the ice sheet. Because radio waves can’t penetrate water, by searching for patches of reflected waves it becomes possible to identify the sheet.
Of the lakes identified, most are stable. But two are active, which means that they fill-up and drain on a cycle. Active lakes are particularly relevant because in Antarctica it is known that some active lakes cause the ice above to flow quicker. ‘For Greenland, that’s our next step,’ says Bowling. ‘We don’t know if they are having a similar effect on the ice.’
She adds that it’s still too soon to make predictions about how the lakes relate to climate change and the melting of the ice sheet, but it is thought that if the lakes migrate further inland they could become increasingly connected to the surface. ‘If there’s a connection and surface water is getting down to the bed more rapidly then there could be a greater impact on ice flow,’ says Bowling.
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