Measuring Isotopic Carbon Dioxide Fluxes Using In Situ Tunable Diode Laser Absorption Spectroscopy

Fluxes of the various stable isotopic forms of carbon dioxide are of interest in studies of carbon dioxide exchange in natural systems. Photosynthesis and respiration affect the isotopic ratios differently. Therefore measuring the flux of various isotopic forms of carbon dioxide can help to partition the net carbon dioxide flux into these two components. Previous measurements have used in situ non-dispersive infrared analysis to measure the total carbon dioxide flux, and mass spectroscopy of samples collected in the field to determine isotopic ratios. The isotopic flux is then inferred from these measurements. Tunable diode laser absorption spectroscopy has the selectivity, sensitivity, and frequency response required to measure the flux of a specific isotopic form of carbon dioxide using either the gradient or eddy covariance technique. Results are given for 13CO2 and C18OO.