What are Icings?


 |  Biodiversity/Conservation

Have you ever seen an icing? Icings are a common feature in northern Canada, yet most of us have never heard of them; I didn’t until I started studying them. Icings or aufeis, form during the winter in Arctic regions and are sheet-like masses of layered ice. They commonly form on top of rivers and streams but can also form on the ground surface.

How do icings form?

Icings form when groundwater under high pressure is pushed to the surface of existing ice or the ground. Water overflows onto the surface, and freezes; these overflow events happen repeatedly throughout the winter, building up ice thickness.  Eventually, entire river channels can be filled with ice 1.

Conditions that favour icing formation include periods of warmer winter air temperatures, low early winter snowfall, and the presence of groundwater springs or pockets of thawing permafrost within the soil 1,2.  Icings can return to the same locations if their water source persists year to year 3.

Icings & Permafrost Thaw

Water flow through pockets of thawing permafrost may produce icings. Permafrost, or ground that remains frozen all year round, is thawing across Northern Canada due to climate warming. Typically, the amount of water flowing through northern waterways during winter is low because of permafrost, which acts as a barrier to the passage of water through the soil. However, thawing permafrost provides brand-new pathways for water to travel through during winter, and may be responsible for the increased level of winter streamflow observed in many northern streams and rivers since the 1970s 4 .

Permafrost acts as a huge store of carbon (nearly 17 billion metric tons) and other chemicals which are all “locked up” when the ground is frozen 5 . As permafrost thaws, these chemicals may be released to waterways and change water quality, and potentially release more CO2 to the atmosphere.

Icings as a Monitoring Tool

Much of the existing research on icings has focused on their distribution, and the factors that influence their formation 2,6–8 . However, icings may also be used as a tool to monitor how permafrost thaw is changing the water chemistry of streams and rivers in winter – which is what I’m studying. At the end of the winter, an icing is a collection of frozen water that represents what was flowing below the ground over the season; if water flowed through thawing permafrost it will have a unique chemical signature.  Thus, if you take ice cores from icings, thaw, and analyze them, you can reveal what winter water chemistry looked like, and see if permafrost thaw is affecting water quality. 

Drilling for icing cores in Yellowknife, NT. (Credit: Nora Alsafi)

Winter is often an understudied period, as there are logistical challenges to sample collection (it’s so cold)! As a result, the nature of winter water chemistry in northern streams is not fully understood; how warming and permafrost thaw are affecting streams in winter is also unclear. Icings may be a useful tool to help answer these questions in the future.


1. Morse PD, Wolfe SA. Icings in the Great Slave Region (1985-2014), Northwest Territories, Mapped from Landsat Imagery.; 2014. doi:10.4095/295540

2. Morse PD, Wolfe SA. Geological and meteorological controls on icing (aufeis) dynamics (1985 to 2014) in subarctic Canada. Journal of Geophysical Research: Earth Surface. 2015;120(9):1670-1686. doi:10.1002/2015JF003534

3. Huryn AD, Gooseff MN, Hendrickson PJ, Briggs MA, Tape KD, Terry NC. <scp> Aufeis </scp> fields as novel groundwater‐dependent ecosystems in the arctic cryosphere. Limnology and Oceanography. 2021;66(3):607-624. doi:10.1002/lno.11626

4. st. Jacques JM, Sauchyn DJ. Increasing winter baseflow and mean annual streamflow from possible permafrost thawing in the Northwest Territories, Canada. Geophysical Research Letters. 2009;36(1):L01401. doi:10.1029/2008GL035822

5. Miner KR, Turetsky MR, Malina E, et al. Permafrost carbon emissions in a changing Arctic. Nature Reviews Earth & Environment. 2022;3(1):55-67. doi:10.1038/s43017-021-00230-3

6. Ensom T, Makarieva O, Morse P, Kane D, Alekseev V, Marsh P. The distribution and dynamics of aufeis in permafrost regions. Permafrost and Periglacial Processes. 2020;31(3):383-395. doi:10.1002/ppp.2051

7. Morse PD, Wolfe SA. Long-Term River Icing Dynamics in Discontinuous Permafrost, Subarctic Canadian Shield. Permafrost and Periglacial Processes. 2017;28(3):580-586. doi:10.1002/ppp.19078.      Crites H, Kokelj S v., Lacelle D. Icings and groundwater conditions in permafrost catchments of northwestern Canada. Scientific Reports. 2020;10(1):3283. doi:10.1038/s41598-020-60322-w

8. Crites H, Kokelj S v., Lacelle D. Icings and groundwater conditions in permafrost catchments of northwestern Canada. Scientific Reports. 2020;10(1):3283. doi:10.1038/s41598-020-60322-w