ARS | Publication request: ESTIMATING THE ISOTOPE RATIO OF ECOSYSTEM RESPIRATION USING THE KEELING PLOT AND THE FLUX RATIO METHOD

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: July 20, 2004
Publication Date: December 14, 2004
Citation: Zhang, J.M., Griffis, T.J., Baker, J.M. 2004. Estimating the isotope ratio of ecosystem respiration using the keeling plot and the flux ratio method. American Geophysical Union. Vol. 85, p. 47.

Technical Abstract: The isotope ratio of ecosystem respiration (delta 13Cr) is a critical parameter in applying stable isotope techniques to study the carbon cycle. It has commonly been determined with the Keeling plot technique, which has limitations related to insufficient range of CO2 concentration and extrapolation of the regression well beyond the data. We have developed a method that uses a newly developed tunable diode laser to directly measure the surface/atmosphere exchange of both stable isotopes of CO2. This provides much better resolution of the temporal dynamics of delta 13Cr and avoids the uncertainties of the Keeling plot method. We found that the methods agreed well in the spring and in the fall when no crop is present, but that they diverged during the growing season, probably due to errors inherent in the Keeling plot approach. The tunable diode laser method will be particularly useful in studying short-term (e.g.- diurnal) variations in carbon cycling.