Researchers have found a surprisingly high rate of melting at the bottom of the Greenland ice sheet, which they attribute to a previously unnoticed factor: the flow of meltwater from the surface to the kilometer-deep bottom of the Greenland ice sheet releases a lot of thermal energy through friction effects, which thaws the ice sheet from below. The scientists say that this should now be incorporated into assessments of how Greenland’s ice loss will continue to develop as a result of climate change.
Studies in recent years have shown that the warm breath of climate change is gnawing at the gigantic ice masses of Greenland. This is known to be associated with great dangers: the enormous amounts of meltwater flowing from the huge island are contributing significantly to the rise in sea level and they could also change the current systems in the North Atlantic in a critical way. The increasing thawing of water surfaces and streams, which form on the Greenland ice sheet in summer, is characterized.
A large part of this mass of water rushes through cracks and large fractures in the ice kilometers deep to the bottom of the ice sheet. It is known that this water can contribute to bottom defrosting. This subglacial fluid is also thought to play another critical role in the development of ice loss: the water acts as a lubricant, increasing the mobility of the slow-moving glacial ice. This means that the more subglacial liquid, the more the ice slides towards the coasts of Greenland.
Insights into processes at the bottom of the glacier
In order to gain new insights into the conditions and processes at the base of the glacial ice and into the importance of meltwater runoff, an international research team carried out investigations on the Store Glacier. This is one of the largest extensions of the Greenland Ice Sheet. To measure the basal melting rates, the researchers used a special radar sounding method. They also took temperature measurements in a borehole in the study area.
When evaluating the data, they were surprised to find that the melt rates observed with the radar at the base of the glacier were often just as high as the values recorded on the surface. This seemed surprising because the surface receives energy in summer, the base does not. The temperature measurements in the borehole also provided further indications of the cause: the researchers determined a water temperature of up to 0.88 degrees Celsius at the base, which appears unexpectedly warm for an ice base.
The researchers then devoted themselves to explaining the findings. According to them, factors such as frictional heat from glacier movement or geothermal energy cannot explain the strong effect. “So far, little attention has been paid to the heat generated by the meltwater itself. Because there is a lot of gravitational energy stored in the water that forms on the surface, and when it falls, that energy has to go somewhere,” says co-author Poul Christoffersen from the University of Cambridge. In principle, this energy potential is also used in hydroelectric power plants to generate electricity via turbines. In contrast, in the case of waterfalls in the ice, the meltwater releases thermal energy through internal frictional activity. The researchers explain that the conversion of kinetic energy into heat is particularly pronounced in the base area of the glacier.
Power like a giant hydroelectric power station
They also devoted themselves to quantifying this factor. They used the calculation of the daily water masses discharged from the Store Glacier in summer as a basis. They came up with a value of up to 82 million cubic meters rushing down to the bottom. From this, the researchers concluded values of the energy release. They estimate that the power generated by the falling water during melt peaks is comparable to that of China’s Three Gorges Dam – the world’s largest hydroelectric power station. “In the case of ice, however, heat is generated that thaws the ice from below,” says Christoffersen.
It can be assumed that this process affects many areas of the huge Greenland ice sheet and is therefore of enormous importance. The study thus reveals a factor in mass loss that has not previously been considered in projections of global sea level rise. And a further intensification is to be expected, as Christoffersen emphasizes in conclusion: “In view of the particularly rapid warming in the high latitudes, the effect of hydropower could easily double or triple,” says Christoffersen.
Source: University of Cambridge, professional article: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2116036119