Meltwater from the surface of an ice cap in Greenland can make its way beneath the ice and become trapped, refilling a subglacial lake. This meltwater provides heat to the bottom of the ice sheet.
The ground-breaking findings, by a team of scientists led by Cornell University Earth and Atmospheric Sciences researcher Michael Willis, provide new information about atmospheric warming and its affect on the critical zone at the base of the ice.
The warmth provided by the water could make the ice sheet move faster and alter how it responds to the changing climate.
“We’re seeing surface meltwater make its way to the base of the ice where it can get trapped and stored at the boundary between the bedrock beneath the ice sheet and the ice itself,” said Willis.
“As the lake beneath the ice fills with surface meltwater, the heat released by this trapped meltwater can soften surrounding ice, which may eventually cause an increase in ice flow.”
The direct link between the surface meltwater and the filling of a lake at the base of the ice has never been seen before.
Over the last few years the number of lakes on the surface of the Greenland ice sheet has greatly increased. Surface lakes are also occurring much farther inland at higher altitudes than in the past.
The Greenland ice sheet comprises about 80% of the land mass of Greenland and previous studies have documented that the ice sheet is melting at a faster rate due to climate change.
This is the first study to document that surface water can penetrate to the bottom of an ice cap and be trapped in place. Researchers say this process could also occur at other large bodies of ice.
Willis started the research when in 2012 he he spotted a 70 metre hole which had formed when a subglacial lake, far beneath the ice surface, emptied.
The presence of such a lake in the far northeast came as a surprise. The ice in the region is too slow, too cold and too thin to allow melting beneath the ice cap.
Between 2012 and 2014, Willis watched as meltwater on the surface of the ice made its way down cracks around the hole and refilled the empty lake basin at the base of the ice cap.
When water was flowing on the surface, the subglacial lake filled. When water stopped flowing on the surface, the subglacial lake stopped refilling.
Each summer scientists see bright blue streams form on the surface of Greenland as warm air melts the ice sheet. What happens to this water when it disappears into cracks in the ice was a mystery.
The research is detailed in a new paper published in the journal Nature.
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