Greenland Ice Sheet is the world’s largest "dam"

A new study led by the University of Cambridge has discovered extremely high rates of melting at the bottom of the Greenland Ice Sheet, caused by the huge quantities of meltwater falling from the surface to the base.

As the meltwater descends from the surface of the ice sheet, through cracks and large fractures that form under the ice, down to the bed located over a kilometer below, energy is converted into heat in a process similar to the generation of hydroelectric power by large dams. This heat leads to phenomenally high rates of melting at the base, making this ice sheet the largest single contributor to global sea level rise.

As part of the EU-funded RESPONDER project, researchers from Cambridge’s Scott Polar Research Institute have been studying for years the meltwater lakes that form on the top of the ice sheet, how and why they drain so fast, and the effect they have on the sheet as global temperatures continue to rise.

“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,” explained study senior author Poul Christoffersen, an expert in the dynamics of glaciers at Cambridge University. “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.”

By using phase-sensitive radio-echo sounding, the scientists measured basal melt rates, and found that they were often just as high as the melt rates measured on the surface with a weather station. According to their calculations, as much as 82 million meters of meltwater were transferred to the bed of the Store Glacier (one of the largest on the Greenland Ice Sheet) every day during the summer of 2014. 

The researchers estimated that the power produced by the falling water from this glacier during peak melt periods was comparable to that produced by the Three Gorges Dam in China, the largest hydroelectric power station in the world. Considering that the entire ice sheet’s melt area expands to nearly a million square kilometers at the height of summer, it produces more hydropower than the world’s ten largest hydroelectric power stations combined.

“Given what we are witnessing at the high latitudes in terms of climate change, this form of hydropower could easily double or triple, and we’re still not even including these numbers when we estimate the ice sheet’s contribution to sea level rise,” concluded Christoffersen.

The study is published in the journal Proceedings of the National Academy of Sciences.

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By Andrei Ionescu, Earth.com Staff Writer