Major new project studies how the Greenland ice sheet responds to shrinking top layer “sponge”

The ice sheet in Greenland faces many changes and one of them is hiding in plain sight - the snowy layer covering most of its surface. Normally acting as a sponge for refreezing meltwater, this layer is important for the overall fate of the ice sheet, but it’s changing in ways researchers currently do not fully understand. Now, a major grant of 13 million Euro from the European Research Council (ERC) enables an international consortium to investigate this problem. The project is led by Professor Michiel van den Broeke from Utrecht University, ad researchers from the Geological Survey of Denmark and Greenland (GEUS), the Alfred Wegener Institute, and the University of Fribourg.

The top layer of the Greenland ice sheet consists of firn, a type of compressed snow with countless air pockets. The firn layer can be up to 100 meters thick and normally acts as a huge sponge, soaking up most of the meltwater created on the ice sheet’s surface each summer. About 90 percent of the entire ice sheet is covered by this firn layer, but as Arctic temperatures rise, this ice-sheet blanket is changing fast. Now, more meltwater is percolating into Greenland’s firn than previously. 

“The Greenland ice sheet’s firn covered area is shrinking and becoming saturated with meltwater. We expect that the firn will lose a great deal of its current meltwater retention ability. We need to find out how the entire ice sheet will react to this”, says Professor William Colgan from GEUS. With different expertise of the four project leaders, the team plans to tackle current challenges of ice sheet hydrology from firn, linking it to subglacial water discharge and its interaction with overall glacier dynamics. The data collected by the consortium, titled FirnMelt, will inform the next round of IPCC assessments and will be made publicly available throughout the project.

Further improvements to firn models require new and innovative observations as well as a new model framework

Filling in the gap

The changes happening in the Greenland ice sheet’s firn layer are currently not being monitored well enough, according to the team of researchers. Most previous firn studies have focused mostly on the highest elevations of the ice sheet, where there is little meltwater. Other studies have focused on the melt zone around the ice-sheet margin. Between these domains lies a vast area of quickly changing firn that researchers know little about.

“FirnMelt is the first large project that focuses on how this area is changing and, even more important, how its changes will affect the entire ice sheet,” says Professor Horst Machguth from the University of Fribourg in Switzerland. He explains that, since the increasing amount of meltwater from the inner part of the ice sheet could potentially reach the underlying glacier bed, it could alter the hydrological system of the entire ice sheet. This could change the velocity at which the ice moves. Since changes in ice flow velocity can impact the amount of ice that discharges into the oceans, in the end, this might be changing Greenland’s sea level contribution. And not in a positive direction.  

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Simulating meltwater runoff from Greenland’s firn into the ocean has been a long-standing challenge within the climate community. Professor Michiel Van den Broeke from Utrecht University notes that “Recent research has shown that the firn models currently in use are too simplistic and neglect many important processes. Any further improvements require new and innovative observations as well as a new model framework, which is what the FirnMelt project will enable.”

Observations and new projections

According to Professor Van den Broeke, the extreme variability in the Greenland ice sheet hydrology has recently taken the researchers by surprise. New observations and models are required to get on top of projecting the shifting fate of Greenland’s firn and meltwater under climate change. The FirnMelt team plans extensive activities to achieve this goal, namely airborne and satellite observations, in-situ observations using novel traverse vehicles, transforming model frameworks from 1D to 3D, coupling a surface firn model with ice sheet hydrology and ice dynamic models, using AI to create computationally efficient emulators of complex firn processes, and making new projections of the fate of Greenland’s ice sheet all the way to the year 2300.

All of this will enable the team to produce the most comprehensive ice-sheet hydrology model of Greenland, following meltwater from the ice-sheet surface to its base, and how it will impact the entire ice sheet. “To be able to simulate the ice sheet hydrology with all its components is something that really drives me. It will be a challenge, but it is THE challenge we need to tackle,” says Professor Angelika Humbert from the Alfred Wegener Institute in Germany. She explains that the project will keep at least twenty senior and early-career researchers busy until 2031, many of them fully engaged by the grant from the ERC. The project formally starts in spring 2026.

Approaching tipping points

To most people, melting of the Greenland ice sheet probably seems like a very distant and abstract concept, but the team members emphasize that the sea-level rise implications of the changing ice sheet are right at our front doors. “We know that there will be a tipping point in the Greenland ice sheet’s response to increasing meltwater,” says Professor Colgan. He elaborates: 

“At some point, the porous near-surface firn will become saturated with refrozen meltwater. We have already seen this happening in Greenland’s smaller glaciers. This will cause subsequent meltwater to run off into the ocean, instead of percolating downwards and being locally retained through refreezing. Hopefully, in six years’ time we’ll be able to better define what this tipping point looks like, in both time and space, for the Greenland ice sheet.”