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[1] This study examines the broad implications of diffusive transport induced fractionations on the interpretation of isotopic processes in the geophysical environment using the example of gaseous CO2 transport in soils. We use a simple model to simulate isotopic transport of CO2 from soil into a headspace chamber, followed by laboratory validation of predicted values. The combined effects of isotopic and concentration gradients results in an observed fractionation of different magnitude than the accepted theoretical diffusion fractionation, which falls continuously during the headspace equilibration period. We show that isotopic data from a non-steady state diffusive environment can be misinterpreted when steady state diffusion models are applied. The simple processes illustrated here can be extended to any isotopic species, and any diffusive environment where some (or full) equilibration takes place between component species.

The temperature dependance of soil respiration has most commonly been addressed using surface flux data, despite the fact that surface flux measurements implicate CO 2 transport and storage effects that may preclude robust assessments of the temperature dependence of soil respiration. Here we examine whether soil respiration might be assessed using soil profile CO 2 production inferred from soil CO 2 concentration profiles. Over the 9-month study period, we observed marked similarities in the temperature response of CO 2 production across four study sites of contrasting vegetation cover and land use.