Carbon Thaw Rate Doubles When Accounting for Subsidence in a Permafrost Warming Experiment

• Published in: Journal of geophysical research. Biogeosciences 2020-06, Vol.125 (6)
• Main Authors: Rodenhizer, Heidi, Ledman, Justin, Mauritz, Marguerite, Natali, Susan M., Pegoraro, Elaine, Plaza, César, Romano, Emily, Schädel, Christina, Taylor, Meghan, Schuur, Edward
• Format: Article
• Language: English
• Subjects: ENVIRONMENTAL SCIENCES; Environmental Sciences & Ecology; Geology
• ISSN: 2169-8953; 2169-8961

Permafrost soils, which are perennially frozen soils found throughout cold regions, contain vast quantities of carbon and ice. When permafrost thaws, carbon can be lost to the atmosphere, contributing to climate change. This means it is important to track permafrost thaw, which is often done using active layer thickness, or the depth of the seasonally thawed surface layer of soil. However, ice volume can be lost from thawing permafrost, causing the soil surface to drop. Conventional measurements do not account for this surface drop, and the rate of thaw could therefore be underestimated. We found that experimentally warmed soils dropped at a rate of 6 cm year-1, mostly due to loss of ice volume and also due to the loss of soil mass. When accounting for the change in soil surface height over time, the full depth of permafrost thaw was 49% greater. The increased depth of thaw resulted in more than twice as much carbon being thawed as was estimated with standard methods that did not account for subsidence. These findings suggest that permafrost is thawing more quickly than long-term records indicate and that this could result in additional carbon release contributing to climate change.