Researchers have observed very high melting rates at the bottom of the Greenland ice sheet, caused by the large amount of snowmelt falling from the surface to the bottom. When the molten metal falls, energy is converted to heat in a process like hydroelectric power generated by a large dam.
An international team of scientists led by the University of Cambridge Meltwater Descending from the surface of the ice sheet to the bed (more than 1 km below) is the largest source of heat under the world’s second largest ice sheet, with staggering results. High rate It melts at that base.
The lubricating effect of snowmelt water has a strong impact on glacier movement and the amount of ice released into the ocean, especially in Greenland, where glaciers are the fastest moving in the world, under a kilometer of ice. Is difficult to measure directly.
This lack of direct measurement makes it difficult to understand the dynamic behavior of the Greenland ice sheet and predict future changes. The Greenland ice sheet is currently the largest single cause of global sea level rise due to ice loss associated with both melting and runoff.
Now, Minutes of the National Academy of SciencesThe Cambridge-led team discovered that the gravitational energy of the snowmelt water formed on the surface is converted to heat as it is transferred to the bottom through large cracks in the ice.
Every summer, as temperatures rise and daily sunlight increases, thousands of melting lakes and streams form on the surface of the Greenland ice sheet. Many of these lakes quickly flow to the bottom of the ice sheet and fall through cracks and large crevices formed in the ice. Due to the continuous supply of water from rivers and rivers, the connection between the surface and the riverbed often remains open.
As part of EU funding Corresponding person In the project, Professor Paul Christophersen of the Scott Polar Research Institute in Cambridge, how and why these melting lakes flow out rapidly, and the overall behavior of the ice sheet as the Earth’s temperature continues to rise. I have been studying the effect on.
Current research, including researchers at Abelistwis University, is the culmination of seven years of research focusing on the Store Glacier, one of the largest exits of the Greenland ice sheet.
“When studying the basic melting of ice sheets and glaciers, we look at heat sources such as friction, geothermal energy, latent heat released where water freezes, and heat loss to the ice above,” Christophersen said. increase. “But what we didn’t actually see was the heat generated by the draining snowmelt water itself. The water formed on the surface stores a lot of gravitational energy, and when the water falls, , The energy has to go somewhere. “
To measure the basal melting rate, researchers used a phase-sensitive echo sounder, a technique developed at the British Antarctic Survey and previously used on the Antarctic floating ice sheet.
“I wasn’t sure if this technology would work on the fast-moving glaciers of Greenland,” said Dr. Tunjan Young, lead author of the radar system on the Store Glacier as part of his PhD. In Cambridge. “Compared to Antarctica, ice deforms very quickly, and in the summer there is a lot of meltwater, which complicates the task.”
The basal melting rate observed by radar was often as high as the melting rate measured on the surface at meteorological stations. However, the surface receives energy from the sun, but the base does not. To explain the results, Cambridge researchers worked with the University of California, Santa Cruz and geological survey scientists in Denmark and Greenland.
Researchers calculated that 82 million cubic meters of snowmelt water moved to the bed of the Store Glacier daily during the summer of 2014. They say that the electricity generated by the water that falls during the peak of snowmelt is the world’s largest hydroelectric power plant, the Three Gorges of the Changjiang River in China. The Greenland ice sheet has a melting area that expands to about 1 million square kilometers in the middle of summer, producing more hydropower than the world’s 10 largest ice sheets. Hydropower Combined stations.
“Given what we are witnessing at high latitudes in terms of climate change, this form of hydropower can easily double or triple, estimating the contribution of the ice sheet to sea level rise. I don’t even include these numbers when I do. ” Christophersen.
To verify the high basal melting rate recorded by the radar system, the team integrated independent temperature measurements from sensors installed in nearby boreholes. At the base, the temperature of the water was found to be as high as +0.88 degrees Celsius. This is unexpectedly warm at ice sheet bases with a melting point of -0.40 degrees Celsius.
“Observations of the borehole have confirmed that the molten water gets hot when it hits the bed,” said Christophersen. “The reason is that the basic drainage system is much less efficient than the crevices and conduits that carry water through the ice. When drainage efficiency drops, frictional heating occurs inside the water itself. This heat source. Excluding from the calculation, the theoretical melting rate estimate was completely double digits. The heat generated by the falling water melts the ice from bottom to top, and the melting rate we report. Is completely unprecedented. “
This study provides the first concrete evidence of an ice sheet mass loss mechanism, which is not yet included in the prediction of global sea level rise. The high melting rate is characteristic of the heat generated by the subglacial drainage channels that carry the surface water, but the amount of surface water produced in Greenland has increased enormously, almost all of which is discharged to the bed.
Rapid foundational melting of the Greenland ice sheet from surface snowmelt drainage, Minutes of the National Academy of Sciences (2022). DOI: 10.1073 / pnas.2116036119..
University of Cambridge
Quote: Accelerating the melt rate will make the Greenland ice sheet the largest “dam” in the world (February 21, 2022).
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Accelerating the melting rate makes the Greenland ice sheet the largest “dam” in the world
Source link Accelerating the melting rate makes the Greenland ice sheet the largest “dam” in the world