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Title: Observations of 14CO 2 in ecosystem respiration from a temperate deciduous forest in Northern Wisconsin

We show that the 14CO 2 composition of plant and soil respiration can be used to determine the residence time of photosynthetically fixed carbon before it is released back to the atmosphere. To estimate the residence time of actively cycled carbon in a temperate forest, we employed two approaches for estimating the Δ 14CO 2 of ecosystem respiration (Δ 14C-R eco) at the Willow Creek AmeriFlux site in Northern Wisconsin, USA. Our first approach was to construct nighttime Keeling plots from subcanopy profiles of Δ 14CO 2 and CO 2, providing estimates of Δ 14C-R eco of 121.7‰ in June and 42.0‰ in August 2012. These measurements are likely dominated by soil fluxes due to proximity to the ground level. Our second approach utilized samples taken over 20 months within the forest canopy and from 396 m above ground level at the nearby LEF NOAA tall tower site (Park Falls, WI). In this canopy-minus-background approach we employed a mixing model described by Miller and Tans (2003) for estimating isotopic sources by subtracting time-varying background conditions. For the period from May 2011 to December 2012 the estimated Δ 14C-R eco using the Miller-Tans model was 76.8‰. Together, these Δ 14C-R ecomore » values represent mean R eco carbon ages of approximately 1–19 years. We also found that heterotrophic soil-respired Δ 14C at Willow Creek was 5–38‰ higher (i.e., 1–10 years older) than predicted by the Carnegie-Ames-Stanford Approach global biosphere carbon model for the 1 × 1 pixel nearest to the site. Finally, this study provides much needed observational constraints of ecosystem carbon residence times, which are a major source of uncertainty in terrestrial carbon cycle models.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Oregon State Univ., Corvallis, OR (United States). Department of Crops and Soil Science
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Center for Accelerator Mass Spectrometry
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Center for Accelerator Mass Spectrometry; Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  4. Univ. of Wisconsin, Madison, WI (United States). Department of Atmospheric and Oceanic Sciences
  5. NOAA Earth System Research Laboratory, Boulder, CO (United States). Global Monitoring Division; Univ. of Colorado, Boulder, CO (United States). CIRES
  6. Univ. of Colorado, Boulder, CO (United States). INSTAAR
Publication Date:
Report Number(s):
Journal ID: ISSN 2169-8953
Grant/Contract Number:
AC52-07NA27344; LDRD 11-ERD-053; 10-06
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Biogeosciences
Additional Journal Information:
Journal Volume: 120; Journal Issue: 4; Journal ID: ISSN 2169-8953
American Geophysical Union
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; Radiocarbon; Keeling plot; AmeriFlux; respiration
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1402188