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Title: Strong regional atmospheric 14C signature of respired CO 2 observed from a tall tower over the midwestern United States

Radiocarbon in CO 2 ( 14CO 2) measurements can aid in discriminating between fast (<1 year) and slower (>5–10 years) cycling of C between the atmosphere and the terrestrial biosphere due to the 14C disequilibrium between atmospheric and terrestrial C. However, 14CO 2 in the atmosphere is typically much more strongly impacted by fossil fuel emissions of CO 2, and, thus, observations often provide little additional constraints on respiratory flux estimates at regional scales. Here we describe a data set of 14CO 2 observations from a tall tower in northern Wisconsin (USA) where fossil fuel influence is far enough removed that during the summer months, the biospheric component of the 14CO 2 budget dominates. We find that the terrestrial biosphere is responsible for a significant contribution to 14CO 2 that is 2–3 times higher than predicted by the Carnegie-Ames-Stanford approach terrestrial ecosystem model for observations made in 2010. This likely includes a substantial contribution from the North American boreal ecoregion, but transported biospheric emissions from outside the model domain cannot be ruled out. The 14CO 2 enhancement also appears somewhat decreased in observations made over subsequent years, suggesting that 2010 may be anomalous. Furthermore, with these caveats acknowledged, we discussmore » the implications of the observation/model comparison in terms of possible systematic biases in the model versus short-term anomalies in the observations. Going forward, this isotopic signal could be exploited as an important indicator to better constrain both the long-term carbon balance of terrestrial ecosystems and the short-term impact of disturbance-based loss of carbon to the atmosphere.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] ;  [2]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. NOAA Earth Systems Research Lab., Boulder, CO (United States); Univ. of Colorado, Boulder, CO (United States)
  4. Univ. of Colorado, Boulder, CO (United States)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Oregon State Univ., Corvallis, OR (United States)
  6. NOAA Earth Systems Research Lab., Boulder, CO (United States)
  7. Univ. of Colorado, Boulder, CO (United States); Univ. of Groningen, Groningen (Netherlands)
  8. Sandia National Lab. (SNL-CA), Livermore, CA (United States); Ramboll Environ U.S. Corp., Novato, CA (United States)
  9. Univ. of Colorado, Boulder, CO (United States); National Isotope Centre, Lower Hutt (New Zealand)
  10. Univ. of California, Irvine, CA (United States)
Publication Date:
Report Number(s):
SAND-2015-9875J; LLNL-JRNL-678969
Journal ID: ISSN 2169-8953; 607986
Grant/Contract Number:
AC04-94AL85000; AC52-07NA27344; LDRD 11-ERD-053; SCW1447; DEAC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Biogeosciences
Additional Journal Information:
Journal Volume: 121; Journal Issue: 8; Journal ID: ISSN 2169-8953
Publisher:
American Geophysical Union
Research Org:
Sandia National Lab. (SNL-CA), Livermore, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
Sandia Internal; USDOE
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 54 ENVIRONMENTAL SCIENCES
OSTI Identifier:
1338304
Alternate Identifier(s):
OSTI ID: 1343024; OSTI ID: 1402240