Researchers have observed extremely high rates of melting at the bottom of the Greenland Ice Sheet, caused by massive quantities of meltwater falling from the surface to the base. As the meltwater falls, heat is generated in a process like the hydroelectric power generated by large dams.
An international team of scientists, led by the University of Cambridge, found that the effect of meltwater descending from the surface of the ice sheet to the bed – a kilometer or more below – is by far the largest heat source beneath the Greenland ice sheet, leading to phenomenally high rates of melting at its base.
The lubricating effect of meltwater has a strong effect on the movement of glaciers and the quantity of ice discharged into the ocean, but directly measuring conditions beneath the ice is a challenge.
In a new study, the Cambridge team has found that the gravitational energy of meltwater forming at the surface is converted to heat when it is transferred to the base through large cracks in the ice.
Each summer, thousands of meltwater lakes and streams form on the surface of the Ice Sheet as temperatures rise and daily sunlight increases.
“When studying basal melting of ice sheets and glaciers, we look at sources of heat like friction, geothermal energy, latent heat released where water freezes and heat losses into the ice above,” explains Christoffersen. “But what we hadn’t really looked at was the heat generated by the draining meltwater itself. There’s a lot of gravitational energy stored in the water that forms on the surface and when it falls, the energy has to go somewhere.”
To measure basal melt rates, the researchers in the study used phase-sensitive radio-echo sounding, a technique developed at the British Antarctic Survey and used previously on floating ice sheets in Antarctica.
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