Snow and Antarctic Lichens

Permafrost is the soil (including rock, organic matter and water in the soil) that remains at temperatures below 0ºC for periods over 2 years. When it melts, it can cause changes in the chemical exchanges between the soil and atmosphere, with the releasing of greenhouse gases, such as carbon dioxide and methane.

Snow has an important role in the soil, as it protects the ground surface from atmospheric processes (such as erosion caused by wind and rain, and energy exchange), and therefore influences the spatial distribution of permafrost. During the austral summer (hot season in the southern hemisphere), when the snow melts, nivation (areas of late snow accumulation), reduce in size. It is also during this time of the year that the Antarctic vegetation, comprised by small plants, have the opportunity to develop.

From all botanic groups (vascular  plants, algae, lichens, mosses and fungi), the lichens group is likely the best adapted to this polar environment due to its high tolerance to cold and dryness. One of the most abundant subgroups of lichens in the Antarctic Peninsula are the fruticose lichens (from the genus Usnea) that resemble small bushes and aggregate creating formations that occupy extensive areas.

One team from the University of Lisbon that focuses on the study of permafrost and climate change in the Antarctic Peninsula (one of the regions on the planet that shows the highest increase in the average air temperatures in the past decades), has been analyzing the relationship between the geographic distribution of these botanic communities and the snow characteristics using cartography and satellite imagery.

The main result in a study conducted in King George Island (South Shetland Arquipelago), shows that the communities of Usnea spp are located frequently on convex surfaces (higher topography), exposed to the wind where conditions are less prone to snow accumulation.

The figure shows a situation where we can easily define the limit of snow accumulation during the cold season, above which we can find the lichens formations, occupying a higher topography. Below this line, we can observe the highest snow accumulation region during the cold season, where snow cover prevails during the summer season in the most concave region.


Source: Vieira G., Mora C., Pina P., Schaefer C.. A proxy for snow cover and winter ground surface cooling: Mapping Usnea sp. communities using high resolution remote sensing imagery (Maritime Antarctica)”. Geomorphology 225 (15-11-2014) : 69–75. doi: 10.1016/j.geomorph.2014.03.049

Author: Ana Salomé