Each summer season, thousands of meltwater lakes and streams form on the surface of the Greenland Ice Sheet as temperature levels increase 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, latent heat released where water freezes and heat losses into the ice above,” said Christoffersen. With a melt area that broadens to nearly a million square kilometers at the height of summer, the Greenland Ice Sheet produces more hydropower than the worlds ten largest 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 completely unprecedented.”
Water streaming into a moulin and down to the bed of Store Glacier, Greenland. Credit: Poul Christoffersen
The worlds second-largest ice sheet is melting from the bottom up– and creating substantial quantities of heat from hydropower.
Researchers have actually observed exceptionally high rates of melting at the bottom of the Greenland Ice Sheet, triggered by huge amounts of meltwater falling from the surface to the base. As the meltwater falls, energy is transformed into heat in a procedure like the hydroelectric power produced by large dams.
A worldwide team of researchers, led by the University of Cambridge, discovered that the effect of meltwater coming down from the surface area of the ice sheet to the bed– a kilometer or more below– is without a doubt the biggest heat source below 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 quantity of ice discharged into the ocean, however directly measuring conditions beneath a kilometer of ice is a difficulty, specifically in Greenland where glaciers are among the worlds fastest moving.
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 forecast future modifications. With ice losses connected to both melting and discharge, the Greenland Ice Sheet is now the biggest single contributor to global water level rise.
Now, in a research study published in the Proceedings of the National Academy of Sciences, the Cambridge-led 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, countless meltwater lakes and streams form on the surface of the Greenland Ice Sheet as temperature levels rise and daily sunlight boosts. A number of these lakes rapidly drain to the bottom of the ice sheet, falling through 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 stay open.
Sketch showing ice sheet hydropower which warms and melts the base of Greenland Ice Sheet much faster than formerly believed possible. Credit: Poul Christoffersen
As part of the EU-funded RESPONDER project, Professor Poul Christoffersen from Cambridges Scott Polar Research Institute has 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 international temperature levels continue to rise.
The existing work, that includes scientists from Aberystwyth University, is the conclusion of a seven-year research study focused on Store Glacier, one of 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, latent heat released where water freezes and heat losses into the ice above,” stated Christoffersen. “But what we had not actually looked at was the heat generated 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.”
To measure basal melt rates, the researchers used phase-sensitive radio-echo sounding, a method established at the British Antarctic Survey and used previously on floating ice sheets in Antarctica.
” We werent sure that the technique would likewise work on a fast-flowing glacier in Greenland,” stated 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 fast and there is a great deal of meltwater in summer season, which makes complex the work.”
The basal melt rates observed with radar were frequently as high as the melt rates measured on the surface area with a weather condition station: however, the surface gets energy from the sun while the base does not. To discuss the results, the Cambridge scientists 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 researchers calculated that as much as 82 million cubic meters of meltwater was transferred to the bed of Store Glacier every day during the summertime of 2014. They approximate the power produced by the falling water during peak melt durations was similar to the power produced by the Three Gorges Dam in China, the worlds biggest hydroelectric power station. With a melt area that broadens to almost a million square kilometers at the height of summertime, the Greenland Ice Sheet produces more hydropower than the worlds 10 largest hydroelectric power stations integrated.
” Given what we are seeing at the high latitudes in terms of climate modification, this type of hydropower could quickly double or triple, and were still not even consisting of these numbers when we estimate the ice sheets contribution to sea level rise,” said Christoffersen.
Science camp on Store Glacier near supraglacial lake on Store Glacier, Greenland. Credit: Tom Chudley
To confirm the high basal melt rates recorded by the radar system, the team incorporated independent temperature measurements from sensing units set up in a neighboring borehole. At the base, they found the temperature level of water to be as high as +0.88 degrees Celsius, which is all of a sudden warm for an ice sheet base with a melting point of -0.40 degrees.
“The reason is that the basal drain system is a lot less effective than the fractures and channels that bring the water through the ice. The heat produced by the falling water is melting the ice from the bottom up, and the melt rate we are reporting is completely unprecedented.”
The study presents the very first concrete proof of an ice-sheet mass-loss mechanism, which is not yet consisted of in projections of global water level rise. While the high melt rates are particular to heat produced in subglacial drainage paths bring surface area water, the volume of surface area water produced in Greenland is big and growing, and nearly all of it drains pipes to the bed.
Referral: “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 study was supported in part by the European Union and the European Research Council.