With the encroaching winter storm and dropping temperatures, I thought it would be appropriate to talk about a very interesting and unique soil order, the Gelisol. Soils are dynamic systems that are essential to life as we know it, and are nonrenewable resource that vary in physical and chemical composition throughout the world. Parent material (underlying bedrock, glacial deposits, wind-blown sediment, etc…), climate, topography, biological activity/factors, and time are the 5 soil forming factors. Different places on the planet will produce a wide variety of variations of these 5 factors. To help understand and classify soils, 12 different orders were formed. The 12 different Soil Taxonomy Orders are: Alfisols, Andisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols, and Vertisols. Each order has unique properties that are a result of 5 soil-forming factors.
Figure 1: Global Distribution of Gelisols (NRCS https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/maps/?cid=stelprdb1237761)
Gelisols are, in my opinion, the most interesting and important soil orders. The Soil Science Society of American defines Gelisols as soils that are “permanently” frozen containing permafrost within 100 centimeters of the soil surface, and/or gelic materials within 100 centimeters and permafrost within 200 centimeters of the soil surface. Permafrost is soil and rock that remains below 0 degrees Celsius for a minimum of 2 years; and “gelic materials” are soil components that show evidence of cryoturbation, or frost churning, a mechanism unique to gelisols. Cryoturbation is the irregular breaking and mixing of soil horizons (think different segmented layers of soil) via the movement of water caused by seasonal melts and thaws. To clarify, just because your front yard is frozen for a few months in the winter is not enough to classify the soil within as a gelisol.
Figure 2: A Gelisol (SSSA https://www.soils.org/discover-soils/soil-basics/soil-types/gelisols)
According to the United States Geological Survey, around 9% of global ice-free land area contain gelisols. They are found in tundra and cold-weather environments, which has made them a hot topic of conversation as the effects of climate change are becoming more obvious. Trapped within the permafrost, contained within gelisols are large amounts of preserved carbon. Over thousands of years, during the last ice age, carbon was deposited in permafrost as ice sheets advanced and retreated. Bedrock was ground into fine silts and dust via glacial movement. This glacial flour was blown across the world and deposited, covering everything in sight, including plants and animals. Quick burial in cold environments doesn’t allow for decomposition of organic material. So as a result, modern day gelisols are a giant carbon reservoir. As climate change continues, the environments containing gelisols are more at risk of melting. Melting gelisols means that the organic material within them are now subject to rapid degradation. The decomposition of organic matter releases carbon in various forms, the most dangerous being methane. Methane is a very powerful greenhouse gas that acts to trap light in heat within our atmosphere. Hopefully you can see the problem: increasing climate change has the potential to thaw gelisols, releasing large reservoirs of methane into the atmosphere, effectively increasing the rate of climate change exponentially. Quite literally adding fuel to the fire.
Figure 3: Babe, the bison was found in thawing permafrost is estimated to be around 36,000 years old. (Photo by: Bill Schmoker (PolarTREC 2010), Courtesy of ARCUS)
-Joe Croze, UConn Soil Lab
Uconnladybug's Blog 