HR: 09:30h
AN: B21C-07    [Abstracts]
TI: The Contribution of Old Carbon to Respiration from Alaskan Tundra Following Permafrost Thaw
AU: * Schuur, E A
EM: tschuur@ufl.edu
AF: University of Florida, Department of Botany 220 Bartram Hall, Gainesville, FL 32611,
AU: Vogel, J G
EM: jvogel@ufl.edu
AF: University of Florida, Department of Botany 220 Bartram Hall, Gainesville, FL 32611,
AU: Crummer, K G
EM: gracec@ufl.edu
AF: University of Florida, Department of Botany 220 Bartram Hall, Gainesville, FL 32611,
AU: Lee, H
EM: hannalee@ufl.edu
AF: University of Florida, Department of Botany 220 Bartram Hall, Gainesville, FL 32611,
AU: Sickman, J O
EM: james.sickman@ucr.edu
AF: University of California, Department of Environmental Sciences, Riverside, CA 92521,
AU: Dutta, K
EM: koushikc14@gmail.com
AF: University of Florida, Department of Botany 220 Bartram Hall, Gainesville, FL 32611,
AB: More than 450 Pg of soil carbon (C) has accumulated in high latitude ecosystems after the retreat of the last major ice sheets. Recent studies suggest that, due to climate warming, these ecosystems may no longer be accumulating C, and in some cases may be losing stored C to the atmosphere. We used radiocarbon measurements of carbon dioxide to detect the age of C respired from tussock tundra near Denali National Park, Alaska. At this tundra site, permafrost has been observed to warm and thaw over the past several decades, causing the ground surface to subside as ice volume in the soil decreased. We established three sites within this area that differed in vegetation and surface topography; both characteristics varied in relation to the degree of permafrost thaw. We made radiocarbon measurements of ecosystem respiration, incubations of soil organic matter, and incubations of above and belowground plant biomass to determine the age and isotopic value of C respired from these sites. Over the study period from 2004 to 2006, ecosystem respiration radiocarbon values averaged from +35‰ to +95‰ in different months across sites. For soil incubations, surface soil radiocarbon was elevated relative both to ecosystem respiration and the current atmospheric radiocarbon value, demonstrating the significant contribution from C fixed over the past years to several decades. The deeper soil, in contrast, had respiration isotope values that averaged below zero, reflecting the significant effect of radioactive decay on the isotope content of deeper soil layers. The plant and soil incubations were combined in a multi- source mixing model to determine probable contributions from these different sources to ecosystem respiration. Deep soil respiration generally averaged between 5-15% of total ecosystem respiration, but reached as high as 40% in some months. When aggregated across the growing season, the two sites undergoing more disturbance from permafrost thaw had on average 2-3 times the loss of old deep C as compared to the least disturbed site.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0475 Permafrost, cryosphere, and high-latitude processes (0702, 0716)
DE: 0708 Thermokarst
DE: 0793 Biogeochemistry (0412, 0414, 1615, 4805, 4912)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting