Austerdalsbreen's dark surface comes to light

by Jacob Yde, January 19, 2022

The dark material on Austerdalsbreen is more fascinating than it may look from afar. Cold-tolerant cyanobacteria, algae, and other microbes colonize the surface of minerals, forming granules called cryoconite. A recent study by Rozwalak and co-authors examines cryoconite on 33 glaciers worldwide, including Austerdalsbreen, to determine the characteristics and variability of these extreme habitats.

Cryoconite are granules on glacier surfaces that consist of both minerals and organic matter. It can often be distinguished from abiotic glacier surface debris due to it leaving a trace of smooth dark organic matter on your fingers if you touch it. The form of cryoconite varies from being almost completely spheric to more irregular shapes. Due to its dark color, cryoconite tends to melt into the ice surface, forming cylindrical depressions called cryoconite holes.

Close-up of cryoconite granules on Austerdalsbreen. Their diameter is between 0.5 and 1.0 cm (photo: K. Zawierucha).

The surface of Austerdalsbreen contains cryoconite material in certain areas near the glacier front, although most surface debris is inorganic and may derive from glacial weathering or dust deposition. In their new study published in Science of the Total Environment, Rozwalak and colleagues find that Austerdalsbreen has larger cryoconite granules than the other sites in the study, although the organic matter content of c. 9% is like many other glaciers. An exceptional feature of the Austerdalsbreen cryoconite is unusually high concentrations of Rare Earth Elements (REEs), only exceeded by REE concentrations in cryoconite from Kersten Glacier on Kilimanjaro. The source of these REEs is unknown and further studies are planned to bring more light into this issue.

Cryoconite holes on the surface of Austerdalsbreen (photo: K. Zawierucha).

Samples of cryoconite were collected by Krzysztof Zawierucha (Adam Michiewicz University in Poznan, Poland) during the JOSTICE 2021 Exploratory Workshop on Austerdalsbreen, as part a multidisciplinary effort with JOSTICE members to better understand the consequences of potential darkening of the Jostedalsbreen Ice Cap surface during glacier thinning and retreat. The cryoconite on Austerdalsbreen has the second darkest color in the study, indicating that expansion of cryoconite cover on the lower part of Austerdalsbreen may accelerate glacier melt rates as the glacier surface becomes darker.