Summers in Greenland are getting longer and warmer due to global climate change. As a result, the meltwater lakes on the surface of the Greenland ice sheet are growing larger, ultimately contributing more to the rise of the global sea level than before.
Meltwater from Greenland's ice sheet is already the single greatest contributor to global sea level rise.
Until now, there has been limited knowledge about how meltwater affects ice movement and sea level rise when it disappears from the lakes on the surface of the ice sheet. However, this has now been illuminated by new research involving DTU scientists, which was recently published in the scientific journal Nature.
”It has been unclear what happens to meltwater from the surface of Greenland's ice sheet when it flows beneath the ice and into the Arctic Ocean, a process that is increasing as Greenland warms. So far, we have not been able to map these processes, but now we can,” says DTU Space professor Shfaqat Abbas Khan, one of the researchers in the international team behind the new mapping of the meltwater flow.
Currently, Greenland loses about five cubic kilometres of ice each week - equivalent to five ice blocks measuring 1x1x1 kilometres.
The water 'lubricates' the ice and accelerates melting
The large Greenland glaciers on the ice sheet, resting on bedrock, slowly slide towards the coast and the surrounding seas. Meltwater that penetrates through the ice contributes both to melting the ice from below and lubricating it, causing the ice to slide more quickly toward the ocean, where it all melts.
The researchers have mapped the processes behind the collection, storage, and release of water within the ice. On its journey through the kilometre-thick ice to the ocean, water from the large meltwater lakes on the surface of the ice sheet undergoes several phases. Along the way, the water can freeze or be otherwise retained in "buffer reservoirs" beneath the ice - and act as a lubricant for the ice's movement.
”The meltwater’s journey to the ocean undergoes multiple stages, which are crucial in determining how climate change ultimately impacts the ice sheet and sea level rise,” says Shfaqat Abbas Khan.
”It's important that we gain insight into this to improve climate models, especially given the longer and warmer summer periods in Greenland, which create larger and more persistent meltwater lakes ”.
It was also found that large amounts of meltwater are temporarily stored along the edge of the ice sheet during the summer, peaking in July before the water gradually reduces and continues its journey.
Danish monitoring stations in Greenland are key to understanding climate change
The measurements that map the path of meltwater through the ice were made using GNET in Greenland, a series of observation stations based on the Global Navigation Satellite System (GNSS), owned by the The Danish Agency for Climate Data and operated in collaboration with DTU.
Using GPS, the GNET stations measure the up-and-down movements of Greenland's bedrock as the ice and water above it changes shape and position. This allows the movement of water flows to be determined.
”Understanding how water is stored and released within the ice sheet has always been challenging. Thanks to GNET data from DTU Space, we can now gain real-time insights into how water accumulates and drains within the ice,” says Pavel Ditmar, a researcher at the Delft University of Technology in the Netherlands and one of the lead authors of the Nature article.
With GNET technology, it is possible to detect bedrock movements over time within fractions of a millimetre.
”GNSS data holds great potential for improving our understanding of these previously unknown hydrological processes in Greenland and can provide the basis for more accurate projections of future ice melt and associated sea level rise in climate models, making them more precise,” confirms Shfaqat Abbas Khan.
The 'Carlsberg Foundation, Semper Ardens Advance program, CF22-0628’ supports the new study.
