Shelef Lab Group continues studies of changing permafrost conditions in the Arctic
By: William Peters
As climate change continues to loom overhead, researchers are trying to answer questions regarding major contributors to future greenhouse gas emissions. Much attention in recent years has focused on a unique landform known as permafrost. Permafrost is a layer of soil below the surface that is frozen year-round due to the low temperatures of the polar regions. In high latitude areas, permafrost makes up roughly 55 million square kilometers of land surface. Thawing of permafrost has the potential to be a significant factor in future climate change scenarios due to the release of carbon and methane contained within the currently frozen organic matter which will have far ranging environmental effects.
Dr. Eitan Shelef, a geomorphologist here at the University of Pittsburgh, is analyzing permafrost in northern circumpolar regions to quantify carbon deposits within the soil. Dr. Shelef specializes in changes of landscape due to erosion and how it relates to climate. While many projections have been made to quantify the amount of permafrost carbon in high latitude polar regions, large uncertainty remains owing to the vast geographical range and varied topography of the Arctic. Dr. Shelef’s research on the connected relationship between erosional processes, climate, and permafrost is incredibly important to accurately estimate the amount of greenhouse gases stored in the ground, and to better understand the importance of thawing permafrost on an already rapidly changing climate.
Permafrost soils in extreme polar regions have been frozen for thousands of years due to year-round average temperatures that are below freezing. When plants absorb carbon dioxide to perform photosynthesis, they store that carbon within the plant. In permafrost regions, this carbon is stored within the frozen ground rather than released back into the atmosphere when the plant dies. However, due to the warming of our atmosphere, the permafrost is thawing. As it thaws, the organic matter and stored carbon from organic matter is emitted in the form of greenhouse gases-namely carbon dioxide (CO2) and Methane (CH4). When carbon is released into the atmosphere, it traps the infrared heat reemitted from the earth in the lower atmosphere, heating the planet. This is becoming increasingly consequential because of its effect on thawing permafrost’s positive feedback loop. As the atmosphere warms, permafrost thaws, releasing organic carbon, which contributes to atmospheric warming, and the cycle accelerates.
Although a large portion of climate research is dedicated to quantifying the amount of carbon that is stored in the frozen soil of the polar regions, significant uncertainties remain in regions of variable landscapes. Dr. Shelef’s recent research is mostly centered in Alaska, where there are areas of great topographic relief. Dr. Shelef analyzes the topography of these regions and studies the erosional patterns of hillslopes to better quantify the amount of carbon accumulated at the base of mountains and hills. As erosion occurs in mountainous and hilly regions, soil accumulates at the bottom of these slopes. This topographic unevenness can drastically increase the amount of organic carbon stored in a small area. These hillslope “toes” continually increase due to annual erosion, increasing the depth of organic carbon in the earth. This potentially creates a great amount of uncertainty as to how much organic matter is located in these accumulation points, due to the variability of erosional processes. While Dr. Shelef’s research is mostly located in Alaska, he believes that these erosional accumulations are located all over polar regions in areas of topographic relief. When in the field, Dr. Shelef spends his days drilling into these soils, analyzing the microbes which decompose organic matter and quantifying the carbon contents of these soils to determine the nature of these deposits. He has discovered great variations in carbon deposit depths within these regions, creating concerns and uncertainty regarding the amount of carbon actually located in the circumpolar region.
Figure 1: The graph above, taken from Dr. Shelef’s publication, portrays the fluidness and movement of the top, active layer of soil, caused by erosion. This “mobile layer” travels down the hillslope, to the “hill-toe” and becomes deposited soil, much deeper than the surface level. (Shelef, et al, 2017).
As questions begin to arise about how to properly analyze these hillslopes and their carbon deposits, Dr. Shelef looks to analyze how the changing climate is affecting the erosional processes that cause these soil accumulations with the help of Dr. Mark Abbott, a stratigrapher here at the University of Pittsburgh. They are looking into how past periods of warmer climate can cause erosion and instability in permafrost soils, and thus cause an increase in the frequency and amplitude of erosional weathering. The excavation of these deep soils can potentially be exposed to the atmosphere as well, releasing ancient carbon deposits.
Dr. Shelef’s research has made significant contributions to our understanding of permafrost landscapes which will contribute to quantifying the impact erosion has on permafrost melting and the future of our climate. The uncertainty that Dr. Shelef’s research has exposed will hopefully lead to an improved understanding of integrated relationship between climate, landscape processes, and carbon cycling. Erosional processes in areas containing large carbon deposits have the potential to greatly impact our climate. Dr. Shelef’s will provide a basis for stronger analyses of the amount of carbon in our planet’s soils and improve future projections of global climate change.
Posted: March 29, 2021