HR: 1340h
AN: B23A-0957    [Abstracts]
TI: Permafrost Melting and the Age of Carbon Respired From Arctic Tundra
AU: * Schuur, E A
EM: tschuur@ufl.edu
AF: University of Florida, 220 Bartram , Gainesville, FL 32611 United States
AU: Dutta, K
EM: kdutta@ufl.edu
AF: University of Florida, 220 Bartram , Gainesville, FL 32611 United States
AU: Vogel, J
EM: ftjgv@ufl.edu
AF: University of Florida, 220 Bartram , Gainesville, FL 32611 United States
AB: Up to 450 Pg of soil carbon (C) has accumulated in high latitude ecosystems after the retreat of the last major ice sheets. This soil C has until now been largely protected from decomposition by cold temperature, waterlogging, and permafrost. 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 hypothesize that sustained transfers of C to the atmosphere that could cause a significant positive feedback to climate change must come from old C, which forms the bulk of the soil pool. We used radiocarbon measurements of carbon dioxide to detect the age of C respired from tussock tundra near Denali National Park, Alaska. At this alpine tundra site, permafrost has been observed to warm and melt 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. These sites represent differences in time since the onset of permafrost melting and/or in the magnitude of ecosystem change. We made radiocarbon measurements of ecosystem respiration and of incubations of above and belowground plant biomass to determine the age of C respired from these sites. Ecosystem respiration radiocarbon values ranged from +58$\permil$ to +114$\permil$ and there was as much variation within a site as there was between sites reflecting the large variability in surface topography at all sites. Respiration from belowground plant biomass had an average value of +83$\permil$ and was significantly higher than the value of +67$\permil$ respired from aboveground plant biomass. Respiration from plant biomass in general was higher than the current atmospheric radiocarbon value of +60$\permil$, suggesting that plant respiration was derived in part from a C storage pool within stems and rhizomes that was more than a year old. Most ecosystem respiration radiocarbon values were higher than values for plant respiration, indicating that the majority of decomposition of soil organic matter was derived from C fixed over the past several decades. In contrast, some individual plots had radiocarbon values below that of plant respiration, suggesting a larger contribution to respiration from organic matter that was more than 50 years old, likely as a result of deeper soil thaw.
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting