‘Unprecedented’ rates of melting have been observed at the bottom of the ice sheet, due to massive amounts of meltwater dripping from the surface, according to the study published in the Proceedings of the National Academy of Sciences.
When melt water falls, its gravitational potential energy is converted into kinetic energy, which eventually causes the water to heat up as it gathers at the base of the ice sheet. In the process, the study found that the Greenland ice sheet produces more energy than the world’s 10 largest hydroelectric dams combined.
“However, you don’t use the heat from falling water to generate electricity. Instead, it melts the ice,” Paul Christophersen, a senior scientist at the University of Cambridge who was involved in the study, told CNN.
During the warmer months, meltwater collects in lakes and streams on the surface of the ice sheet. Some of this water flows to the bottom of the ice sheet, falling through the cracks and large fractures that form in the ice with movement and pressure.
Melt water contributes to further melting at the bottom of the ice sheet, and also acts as a lubricant that promotes faster flow and increases the amount of ice that is discharged into the ocean.
Kristofferson explained that when looking for ice sheet melt and glaciers at their bases, studies tend to focus on external heat sources.
“But what we haven’t really looked at is the heat generated by the meltwater discharge itself,” he said. “There is a lot of energy stored in the water that forms on the surface, and when it falls, the energy has to go somewhere.”
“Greenland ice is melting at the surface faster than it can keep up with snowfall, so there is a very large loss of melt,” Kristofferson told CNN. “In a large portion of the ice, we get melt rates that can be as high as five or six centimeters per day.”
However, direct measurement of conditions at the base – about one kilometer below the surface – poses challenges, particularly in Greenland, where the glaciers are among the world’s fastest moving.
The Cambridge researchers collaborated with scientists at the University of California Santa Cruz and the Geological Survey of Denmark and Greenland to conduct this study. She focused on Store Glacier, a large outlet of the ice cap in Greenland.
To measure melt rates, the researchers used a technique developed at the British Antarctic Survey called phase-sensitive radio-echo sounding, a process by which they can measure the thickness of the ice.
It’s a method previously used on ice sheets floating around Antarctica.
“We weren’t sure this technology would also work on a fast-flowing Greenland glacier,” said Tun Gan Young, the study’s first author, who installed the radar system at Store Glacier.
“Compared to Antarctica, the ice deforms very quickly, and there is a lot of meltwater in the summer, which complicates the work.”