Water streaming into a moulin and down to the bed of Store Glacier, Greenland. Credit: Poul Christoffersen
Researchers have actually observed exceptionally high rates of melting at the bottom of the Greenland Ice Sheet, brought on by substantial quantities of meltwater falling from the surface to the base. As the meltwater falls, energy is transformed into heat in a process like the hydroelectric power produced by big dams.
An international group of scientists, led by the University of Cambridge, found that the effect of meltwater descending from the surface area of the ice sheet to the bed– a kilometer or more below– is by far the biggest heat source underneath the worlds second-largest ice sheet, causing phenomenally high rates of melting at its base.
The lubricating effect of meltwater has a strong result on the motion of glaciers and the amount of ice released into the ocean, but directly measuring conditions underneath a kilometer of ice is a challenge, especially in Greenland where glaciers are amongst the worlds fastest moving.
To determine basal melt rates, the scientists used phase-sensitive radio-echo sounding, a method established at the British Antarctic Survey and used previously on drifting ice sheets in Antarctica.
” We werent sure that the strategy would likewise work on a fast-flowing glacier in Greenland,” stated very first author Dr. Tun Jan Young, who installed the radar system on Store Glacier as part of his PhD at Cambridge. “Compared to Antarctica, the ice warps truly quick and there is a great deal of meltwater in summertime, which complicates the work.”
The basal melt rates observed with radar were often as high as the melt rates determined on the surface with a weather condition station: however, the surface receives energy from the sun while the base does not. To discuss the outcomes, the Cambridge researchers teamed up with researchers at the University of California Santa Cruz and the Geological Survey of Denmark and Greenland.
Tents with supraglacial lake on Store Glacier, Greenland. Credit: Tom Chudley
The scientists determined that as much as 82 million cubic meters of meltwater was transferred to the bed of Store Glacier every day throughout the summer season of 2014. They approximate the power produced by the falling water throughout peak melt periods was similar to the power produced by the Three Gorges Dam in China, the worlds biggest hydroelectric power station. With a melt area that expands to almost a million square kilometers at the height of summer season, the Greenland Ice Sheet produces more hydropower than the worlds ten largest hydroelectric power stations combined.
” Given what we are seeing at the high latitudes in regards to environment modification, this type of hydropower might quickly double or triple, and were still not even including these numbers when we estimate the ice sheets contribution to sea level rise,” stated Christoffersen.
Science camp on Store Glacier near supraglacial lake on Store Glacier, Greenland. Credit: Tom Chudley
To verify the high basal melt rates recorded by the radar system, the group integrated independent temperature level measurements from sensing units installed in a nearby borehole. At the base, they discovered the temperature of water to be as high as +0.88 degrees Celsius, which is unexpectedly warm for an ice sheet base with a melting point of -0.40 degrees.
” The borehole observations confirmed that the meltwater warms up when it hits the bed,” said Christoffersen. “The factor is that the basal drainage system is a lot less efficient than the fractures and channels that bring the water through the ice. The minimized drainage effectiveness causes frictional heating within the water itself. When we took this heat source out of our computations, the theoretical melt rate estimates were a complete two orders of magnitude out. The heat generated by the falling water is melting the ice from the bottom up, and the melt rate we are reporting is completely extraordinary.”
The research study presents the first concrete proof of an ice-sheet mass-loss system, which is not yet consisted of in forecasts of worldwide sea level increase. While the high melt rates specify to heat produced in subglacial drain paths bring surface area water, the volume of surface water produced in Greenland is substantial and growing, and nearly all of it drains to the bed.
Reference: “Rapid basal melting of the Greenland Ice Sheet from surface area meltwater drain” 21 February 2022, Proceedings of the National Academy of Sciences.DOI: 10.1073/ pnas.2116036119.
The research was supported in part by the European Union and the European Research Council.
Each summer season, thousands of meltwater lakes and streams form on the surface of the Greenland Ice Sheet as temperature levels rise and daily sunlight increases. Numerous of these lakes rapidly drain to the bottom of the ice sheet, falling through fractures and big fractures which form in the ice.” When studying basal melting of ice sheets and glaciers, we look at sources of heat like friction, geothermal energy, hidden heat released where water freezes and heat losses into the ice above,” stated Christoffersen. With a melt area that expands to nearly a million square kilometers at the height of summer season, the Greenland Ice Sheet produces more hydropower than the worlds 10 biggest hydroelectric power stations combined.
The heat generated by the falling water is melting the ice from the bottom up, and the melt rate we are reporting is totally unprecedented.”
Front of Store Glacier after large calving occasion. Credit: Poul Christoffersen
This lack of direct measurements makes it challenging to comprehend the dynamic behavior of the Greenland Ice Sheet and anticipate future modifications. With ice losses tied to both melting and discharge, the Greenland Ice Sheet is now the largest single contributor to international sea level rise.
Now, in a study published in the Proceedings of the National Academy of Sciences, the Cambridge-led team has discovered that the gravitational energy of meltwater forming at the surface area is converted to heat when it is transferred to the base through large fractures in the ice.
Each summertime, thousands of meltwater lakes and streams form on the surface of the Greenland Ice Sheet as temperatures rise and daily sunshine increases. Much of these lakes quickly drain to the bottom of the ice sheet, failing fractures and large fractures which form in the ice. With a continued supply of water from streams and rivers, connections in between surface and bed often remain open.
Sketch illustrating ice sheet hydropower which warms and melts the base of Greenland Ice Sheet much faster than previously thought possible. Credit: Poul Christoffersen
As part of the EU-funded RESPONDER task, Professor Poul Christoffersen from Cambridges Scott Polar Research Institute has actually been studying these meltwater lakes, how and why they drain so rapidly, and the impact that they have on the overall habits of the ice sheet as worldwide temperatures continue to increase.
The existing work, that includes researchers from Aberystwyth University, is the conclusion of a seven-year study concentrated on Store Glacier, among the largest outlets from the Greenland Ice Sheet.
” When studying basal melting of ice sheets and glaciers, we look at sources of heat like friction, geothermal energy, hidden heat launched where water freezes and heat losses into the ice above,” stated Christoffersen. “But what we had not actually took a look at was the heat produced by the draining pipes meltwater itself. Theres a great deal of gravitational energy saved in the water that forms on the surface and when it falls, the energy has to go somewhere.”