In higher elevations, firn, frozen water that is something between snow and ice, covers the top of glaciers. Firn plays a critical role in regulating glacial meltwater and sea level rise.
It does this by absorbing meltwater, the water released by melting glaciers. The ability of the firn layer to absorb meltwater — its “sponginess” — can be determined by the amount of pore space available, which is impacted by several variables such as temperature, firn grain size and presence of ice layers within the firn layer. A more spongy firn layer allows for more meltwater to be stored as it trickles down and refreezes when it reaches colder temperatures at depth.
Layers of firn can exist between refrozen ice layers. The greater the number of refrozen ice layers there are embedded within the firn layer, the more intense a melt period has been. These layers can act as a barrier against meltwater being stored within the spongy firn layer, forcing the meltwater to flow to lower elevations, eventually exiting the glacier as runoff into the ocean.
Glacial loss
The Devon Ice Cap is located within Inuit Nunangat, the homelands of the Inuit. It is one of the largest ice caps in the Canadian Arctic at approximately 14,000 square kilometres in area and with a maximum thickness of approximately 880 metres.
The Devon Ice Cap is one of many ice masses that play a vital role in the Arctic ecosystem, including in the nearshore marine ecosystem.
(Glacier Atlas of Canada/Government of Canada)
Our research team found that the Devon Ice Cap in Nunavut experienced a decrease in the amount of refrozen glacial meltwater in its firn layer. This was caused by the cooler-than-average summer air temperatures the region experienced in 2021.
Air temperature and glacier melt are closely related, and our research shows how the firn layer is affected by climate changes. It also highlights the fact that climate change does not happen in a linear fashion. Rather, temperatures fluctuate while trending globally towards glacial loss.
Comparing data
We observed how much ice was in the firn layer by extracting six shallow firn cores from different elevations in 2022 and comparing them to cores extracted in 2012.
We found that at the lowest elevation sites on the ice cap (1,400 metres above sea level), where air temperatures are expected to be warmer than at higher elevations, the amount of refrozen meltwater content decreased by nearly 30 per cent. Conversely, at the highest elevation site (1,800 metres above sea level, where temperatures are colder), the decrease was about 11 per cent. These changes occurred despite higher average summer temperatures between 2012 and 2022.
(B. Danielson), CC BY
Greenland Ice Sheet
A similar pattern was also observed on the Greenland Ice Sheet in 2019. Researchers there found less glacial meltwater had refrozen within the firn layer along several points.
The decrease in frozen meltwater seen in the Greenland Ice Sheet’s firn layer had also occurred during a time of less surface melt. Less surface melt in one year can help to increase meltwater storage in the firn layer in following years.
Overall, it was found that in the long term, the Greenland Ice Sheet is more sensitive to warming than cooling. In other words, one extreme year of summer heat had a greater impact on the amount of meltwater compared to other cooler years when meltwater was temporarily stored.
Eventually, the Greenland Ice Sheet and other ice masses across the globe will reach a peak refreezing point, where meltwater can no longer be stored within the firn layer because so much has already accumulated, creating an impermeable layer of ice. Instead of this water being stored in the firn layer, it will run through and off the glacier.
Future measurements
Our findings show how the firn layer responds to one summer of below-average air temperatures. A reduction in the amount of refrozen glacial meltwater stored means an increase in the glacier’s capacity to store meltwater for the next season. This demonstrates the firn layer’s ability to potentially reduce meltwater runoff during a given year.
The future of the glaciers and ice caps in the Canadian Arctic will depend on changes in global temperatures and how glacial physical processes respond. The Canadian Arctic consists of 14 per cent of the world’s glaciers and ice caps by volume, and melting glaciers in the region are projected to be one of the greatest contributors to sea-level rise in the next century.
A better understanding of firn processes and changes in porosity will help researchers quantify how much and when sea level rises are expected from the Canadian Arctic glaciers.
The post “Warming temperatures affect glaciers’ ability to store meltwater, contributing to rising sea levels” by Danielle Halle, PhD Candidate, Glaciology, University of Waterloo was published on 09/01/2025 by theconversation.com