Accelerated melting makes Greenland’s ice sheet the world’s largest dam

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Researchers observe extremely high melting rates at the bottom of the Greenland ice sheet, caused by huge amounts of melt water falling from the surface to the ground. As the melt water falls, the energy is converted into heat in a process similar to the hydroelectric power generated by large dams.

An international team of scientists led by the University of Cambridge has found that the effect of submerged water sinking from the surface of the ice sheet to the bottom – a mile or so below – is by far the largest heat source below the world’s second largest. layer of ice, resulting in surprisingly high rates at its base.

The lubricating effect of melt water has a strong effect on glacier movement and the amount of ice dumped into the ocean, but measuring conditions directly under a kilometer of ice is a challenge, especially in Greenland, where glaciers are among the fastest moving. in the world. world.

This lack of direct measurements makes it difficult to understand the dynamic behavior of the Greenland ice sheet and predict future changes.

The gravitational energy of the molten water formed on the surface is converted into heat when it is transferred to the base through large cracks in the ice.

Every summer, thousands of melt lakes and streams form on the surface of the Greenland ice sheet as temperatures rise and daily sunlight rises. Many of these lakes drain quickly to the bottom of the ice sheet, falling through cracks that form in the ice. With a constant flow of water from streams and rivers, the connections between the surface and the canal often remain open.

To measure basal melting rate, the researchers used sensitive phase radio sounds, a technique developed by the British Antarctic Survey that had previously been used on floating ice sheets in Antarctica.

The basic melting rates observed by radar were often as high as those measured at the surface by a meteorological station: however, the surface receives energy from the Sun and the base does not.

To explain the results, Cambridge researchers worked with scientists from the University of California, Santa Cruz and the Geological Institute of Denmark and Greenland.

The researchers estimated that up to 82 million cubic meters of melt water was transported to the bottom of the Stor Glacier every day during the summer of 2014. They estimated that the energy produced by falling water during peak periods was comparable to that produced from Three Gorges Dam in China, the largest hydroelectric plant in the world.

With a melting point that extends to nearly a million square miles in the middle of summer, Greenland’s ice sheet produces more hydroelectric power than the world’s ten largest hydroelectric plants combined.

To test the high basal melting rate recorded by the radar system, the team incorporated independent temperature measurements from sensors installed in a nearby well. At the base, they found that the water temperature reached 0.88 degrees Celsius, which is unexpectedly hot for the base of a layer of ice with an ice melting point of 0.40 degrees.

Drilling observations have confirmed that the melt water heats up as it enters the basement.

The heat emitted by the falling water melts the ice from the bottom up and the melting rate we report is completely unprecedented, scientists say.

The study provides the first specific data on the mechanism of ice sheet mass loss.

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