U.S. Department of Energy Office of Biological and Environmental Research

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Strong Atmospheric 14C Signature of Respired CO2 Observed over Midwestern United States
Published: August 13, 2016
Posted: November 07, 2016

Terrestrial biosphere contributes a higher amount of atmospheric CO2 than predicted by an ecosystem model.

The Science
A recent study demonstrates a novel methodology for constraining the net exchange of CO2 between the landscape and atmosphere using 14CO2 observed from a tall tower in the midwestern United States. Exchanges include net ecosystem respiration (including belowground carbon), fires, and anthropogenic sources.

The Impact
The study determined that soil respiration of carbon drives variability in 14CO2 during the summer months and that simulations from the Carnegie-Ames-Stanford Approach (CASA) model underestimate the biospheric 14CO2 source compared to observations at the Wisconsin Tall Tower. This approach has the potential to better constrain the long-term carbon balance of terrestrial ecosystems and the short-term impact of disturbance-based loss of carbon to the atmosphere, and highlights areas for continued land-surface/biogeochemistry model development. 

A recent study found that during the summer months the biospheric component dominates the atmospheric 14CO2 budget at the Park Falls AmeriFlux/WLEF Tall Tower in northern Wisconsin. Respiration of carbon from soils is an important component of the global carbon cycle, returning carbon previously taken up via photosynthesis over decadal time scales back to the atmosphere. For 2010, observations from 400 m aboveground indicate that the terrestrial biosphere was responsible for a 2 to 3 times higher contribution to total 14CO2 than predicted by the CASA terrestrial ecosystem model. This finding indicates that the model is underpredicting ecosystem respiration and net primary production. Based on back-trajectory analyses, this bias 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 14CO2 enhancement also appears somewhat decreased in observations made over subsequent years, suggesting that 2010 may be anomalous. 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.

BER PM Contacts
Daniel Stover and Jared DeForest
Daniel.Stover@science.doe.gov (301-903-0289); and Jared.DeForest@science.doe.gov (301-903-1678)

PI Contacts
Karis McFarlane
Lawrence Livermore National Laboratory
kjmcfarlane@llnl.gov (925-423-6285)

Brian LaFranchi
Now at Aclima
brian.lafranchi@gmail.com (802-310-7083)

Tom Guilderson
Lawrence Livermore National Laboratory
guilderson1@llnl.gov (925-422-1753)

This work was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Science Division, Terrestrial Ecosystem Science program (SCW1447); Lawrence Livermore National Laboratory Lab Directed Research and Development (ERD-14-038); National Oceanic and Atmospheric Administration (NOAA) ESRL Global Monitoring Division; and NOAA Climate Program Office's Atmospheric Chemistry, Carbon Cycle.

LaFranchi, B. W., K. J. McFarlane, J. B. Miller, S. J. Lehman, C. L. Phillips, A. E. Andrews, P. P. Tans, H. Chen, Z. Liu, J. C. Turnbull, X. Xu, and T. P. Guilderson. 2016. “Strong Regional Atmospheric 14C Signature of Respired CO2 Observed from a Tall Tower over the Midwestern United States,” Journal of Geophysical Research: Biogeosciences 122(8), 2275-95. DOI: 10.1002/2015JG003271. (Reference link)

Related Links
LEF Tower Data

Topic Areas:

  • Research Area: Earth and Environmental Systems Modeling
  • Research Area: Terrestrial Ecosystem Science
  • Research Area: Carbon Cycle, Nutrient Cycling

Division: SC-23.1 Climate and Environmental Sciences Division, BER


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