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Allocation of Terrestrial Carbon Sources Using 14CO2: Methods, Measurement, and Modeling

Published online by Cambridge University Press:  09 February 2016

Scott J Lehman
Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA
John B Miller
NOAA Earth System Research Laboratory, Boulder, Colorado, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
Chad Wolak
Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA
John Southon
Keck AMS Facility, University of California, Irvine, California, USA
Pieter P Tans
NOAA Earth System Research Laboratory, Boulder, Colorado, USA
Stephen A Montzka
NOAA Earth System Research Laboratory, Boulder, Colorado, USA
Colm Sweeney
NOAA Earth System Research Laboratory, Boulder, Colorado, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
Arlyn Andrews
NOAA Earth System Research Laboratory, Boulder, Colorado, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
Brian LaFranchi
Lawrence Livermore National Lab, Livermore, California, USA
Thomas P Guilderson
Lawrence Livermore National Lab, Livermore, California, USA
Jocelyn C Turnbull
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA National Isotope Centre, GNS Science, Lower Hutt, New Zealand


The radiocarbon content of whole air provides a theoretically ideal and now observationally proven tracer for recently added fossil-fuel-derived CO2 in the atmosphere (Cff). Over large industrialized land areas, determination of Cff also constrains the change in CO2 due to uptake and release by the terrestrial biosphere. Here, we review the development of a Δ14CO2 measurement program and its implementation within the US portion of the NOAA Global Monitoring Division's air sampling network. The Δ14CO2 measurement repeatability is evaluated based on surveillance cylinders of whole air and equates to a Cff detection limit of <0.9 ppm from measurement uncertainties alone. We also attempt to quantify additional sources of uncertainty arising from non-fossil terms in the atmospheric 14CO2 budget and from uncertainties in the composition of “background” air against which Cff enhancements occur. As an example of how we apply the measurements, we present estimates of the boundary layer enhancements of Cff and Cbio using observations obtained from vertical airborne sampling profiles off of the northeastern US. We also present an updated time series of measurements from NOAA GMD's Niwot Ridge site at 3475 m asl in Colorado in order to characterize recent Δ14CO2 variability in the well-mixed free troposphere.

Atmospheric Carbon Cycle
Copyright © 2013 by the Arizona Board of Regents on behalf of the University of Arizona 

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