Scientists 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 melt water from the surface to the kilometer-deep bottom of the Greenland ice sheet releases a lot of heat energy thanks to frictional effects that thaw the ice sheet from below. Scientists say this should now be taken into account when assessing the further development of Greenland’s ice loss as a result of climate change.
Research in recent years has shown that the warm breeze of climate change is chewing on the giant ice sheets of Greenland. This is known to be associated with great dangers: the enormous amounts of meltwater flowing off a huge island contribute significantly to sea level rise and could also critically alter current systems in the North Atlantic. The increasing thawing of the water surface and streams that form on the Greenland ice sheet during the summer was characterized.
A large part of this mass of water flows through crevices and large crevices in the ice deep into the ice to the bottom of the ice sheet. It is known that this water can contribute to the defrosting of the bottom. This subglacial fluid is also believed to play another key role in the evolution of ice loss: water acts as a lubricant, increasing the mobility of slow-moving glacial ice. This means that the more subglacial the liquid, the more the ice moves towards the Greenland coast.
Insight into the processes taking place at the bottom of the glacier
To gain new insight into the conditions and processes at the base of the glacier ice and the importance of melt runoff, an international research team conducted a study at the Store Glacier. It is one of the largest extensions of the Greenland ice sheet. Scientists used a special radar sounding method to measure basal melting rates. They also took temperature measurements in the borehole in the study area.
When evaluating the data, they were surprised to find that the melting rates observed with radar at the base of the glacier were often as high as those recorded at the surface. This seemed surprising because in summer the surface receives energy and the base does not. Temperature measurements at the wellbore also provided further clues to the cause: scientists determined the water temperature at the base to 0.88 degrees Celsius, which appears unexpectedly warm for an icy base.
Scientists then dedicated themselves to explaining the results. According to them, factors such as frictional heat from glacier motion or geothermal energy cannot explain the strong effect. “So far, little attention has been paid to the heat produced by the melt water alone. Because there is a lot of gravitational energy in the water that forms on the surface, and when it falls, that energy has to go somewhere, ‘says co-author Poul Christoffersen of the University of Cambridge. In principle, this energy potential is also used in hydropower plants to generate electricity by turbines. In contrast, in the case of ice waterfalls, the melt water releases thermal energy through internal friction. The scientists explain that the conversion of kinetic energy to heat is especially pronounced in the base zone of the glacier.
Power like a giant hydroelectric plant
They also devoted themselves to quantifying this factor. They used the calculation of the daily mass of water discharged from the Store glacier in the summer period as a basis. They came up with a value of up to 82 million cubic meters rushing to the bottom. From this, the scientists deduced the energy release values. They estimate that the power generated by falling water during melting peaks is comparable to that of China’s Three Gorges Dam – the world’s largest hydropower plant. “However, ice produces heat which defrosts 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 great importance. The study therefore reveals a weight loss factor that has not previously been accounted for in forecasting global sea level rise. And further intensification is to be expected, as Christoffersen concludes: “Due to particularly rapid warming at high latitudes, the impact of hydropower can easily double or triple,” says Christoffersen.
Source: University of Cambridge, Article: Proceedings of the National Academy of Sciences, doi: 10.1073 / pnas.2116036119