Assessing the Potential for Mobilization of Old Soil Carbon After Permafrost Thaw: A Synthesis of 14C Measurements From the Northern Permafrost Region

• Published in: Global Biogeochemical Cycles
• Main Authors: Estop‐Aragonés, Cristian, Olefeldt, David, Abbott, Benjamin W., Chanton, Jeffrey P., Czimczik, Claudia I., Dean, Joshua F., Egan, Jocelyn E., Gandois, Laure, Garnett, Mark H., Hartley, Iain P., Hoyt, Alison, Lupascu, Massimo, Natali, Susan M., O'Donnell, Jonathan A., Raymond, Peter A., Tanentzap, Andrew J., Tank, Suzanne E., Schuur, Edward A. G., Turetsky, Merritt, Anthony, Katey Walter, 1 Department of Renewable Resources University of Alberta Edmonton Canada, 3 Department of Plant and Wildlife Sciences Brigham Young University Provo UT USA, 4 Department of Earth Ocean and Atmospheric Science Florida State University Tallahassee FL USA, 5 Department of Earth System Science University of California Irvine CA USA, 6 School of Environmental Sciences University of Liverpool Liverpool UK, 7 Department of Earth Sciences Dalhousie University Halifax Canada, 8 Laboratoire Ecologie Fonctionnelle et Environnement Université de Toulouse, CNRS Toulouse France, 9 NEIF Radiocarbon Laboratory, Scottish Enterprise Technology Park, Rankine Avenue East Kilbride UK, 10 Geography, College of Life and Environmental Sciences University of Exeter Exeter UK, 11 Max Planck Institute for Biogeochemistry Jena Germany, 12 Department of Geography National University of Singapore Singapore Singapore, 13 Woodwell Climate Research Center Falmouth MA USA, 14 National Park Service, Arctic Network Anchorage AK USA, 15 Yale School of Forestry and Environmental Studies New Haven CT USA, 16 Ecosystems and Global Change Group, Department of Plant Sciences University of Cambridge Cambridge UK, 17 Department of Biological Sciences University of Alberta Edmonton Canada, 18 Department of Biological Sciences Northern Arizona University Flagstaff AZ USA, 19 Department of Integrative Biology University of Guelph Guelph Canada, 20 Water and Environmental Research Center University of Alaska Fairbanks Fairbanks AK USA
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: ddc:551.9; permafrost thaw; radiocarbon; carbon dioxide; methane; dissolved organic carbon; particulate organic carbon; permafrost; Thermokarst; Tundra
• Online Access: https://doi.org/10.23689/fidgeo-4005; http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/8345

The magnitude of future emissions of greenhouse gases from the northern permafrost region depends crucially on the mineralization of soil organic carbon (SOC) that has accumulated over millennia in these perennially frozen soils. Many recent studies have used radiocarbon (14C) to quantify the release of this “old” SOC as CO2 or CH4 to the atmosphere or as dissolved and particulate organic carbon (DOC and POC) to surface waters. We compiled ~1,900 14C measurements from 51 sites in the northern permafrost region to assess the vulnerability of thawing SOC in tundra, forest, peatland, lake, and river ecosystems. We found that growing season soil 14C‐CO2 emissions generally had a modern (post‐1950s) signature, but that well‐drained, oxic soils had increased CO2 emissions derived from older sources following recent thaw. The age of CO2 and CH4 emitted from lakes depended primarily on the age and quantity of SOC in sediments and on the mode of emission, and indicated substantial losses of previously frozen SOC from actively expanding thermokarst lakes. Increased fluvial export of aged DOC and POC occurred from sites where permafrost thaw caused soil thermal erosion. There was limited evidence supporting release of previously frozen SOC as CO2, CH4, and DOC from thawing peatlands with anoxic soils. This synthesis thus suggests widespread but not universal release of permafrost SOC following thaw. We show that different definitions of “old” sources among studies hamper the comparison of vulnerability of permafrost SOC across ecosystems and disturbances. We also highlight opportunities for future 14C studies in the permafrost region. Key Points: We compiled ~1,900 14C measurements of CO2, CH4, DOC, and POC from the northern permafrost region. Old carbon release increases in thawed oxic soils (CO2), thermokarst lakes (CH4 and CO2), and headwaters with thermal erosion (DOC and POC). Simultaneous and year‐long 14C analyses of CO2, CH4, DOC, and POC are needed to assess the vulnerability of permafrost carbon across ...