Iso-FD: A novel method for measuring the isotopic signature of surface flux

Stable carbon isotopes have become a critical and often used tool in understanding ecological and physical processes affecting gas production and emissions in soil. While the insights gained using chamber based flux methods have been significant, it is known now that many of these chamber methods have an inherent bias that complicates the interpretation of their measurements. Here we present a new chamber method that uses diffusive membranes to control CO2 flow into and out of the chamber, and can measure the isotopic composition of soil flux without inducing a bias. We present numerical modeling, followed by laboratory calibration and field measurements using this new method coupled to a Cavity Ring Down Spectrometer (CRDS). Simulations, as well was lab and field results showed that the method is both robust over a range of environmental conditions and can be unbiased, unlike other chamber approaches. Finally, we discuss possibilities for future improvements and variations on the measurement approaches we used. •A novel approach (Iso-FD) for measuring the isotopic composition of soil CO2 flux was developed.•Iso-FD shows minimal bias compared many other chamber systems.•Lab and field experiments confirm that the approach is robust under a range of conditions.