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Title: Observations of 14 CO 2 in ecosystem respiration from a temperate deciduous forest in Northern Wisconsin: Δ14C of ecosystem respiration

The 14CO2 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 Δ14CO2 of ecosystem respiration (Δ14C-Reco) at the Willow Creek AmeriFlux site in Northern Wisconsin, USA. Our first approach was to construct nighttime Keeling plots from subcanopy profiles of Δ14CO2 and CO2, providing estimates of Δ14C-Reco 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 Δ14C-Reco using the Miller-Tans model was 76.8‰. Together, these Δ14C-Reco values represent mean Reco carbon ages of approximately 1–19 years. We also found that heterotrophic soil-respired Δmore » 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. 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
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Department of Crops and Soil Science, Oregon State University, Corvallis Oregon USA
  2. Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore California USA
  3. Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore California USA; Now at Combustion Research Facility, Sandia National Laboratory, Livermore California USA
  4. Department of Atmospheric and Oceanic Sciences, University of Wisconsin, Madison Wisconsin USA
  5. Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder Colorado USA; CIRES, University of Colorado Boulder, Boulder Colorado USA
  6. INSTAAR, University of Colorado Boulder, Boulder Colorado USA
Publication Date:
Report Number(s):
LLNL-JRNL-741230
Journal ID: ISSN 2169-8953
Grant/Contract Number:
AC52-07NA27344; LDRD 11-ERD-053; 10-06; LLNL-JRNL-637140
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Biogeosciences
Additional Journal Information:
Journal Volume: 120; Journal Issue: 4; Journal ID: ISSN 2169-8953
Publisher:
American Geophysical Union
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES
OSTI Identifier:
1409977
Alternate Identifier(s):
OSTI ID: 1402188