Bulk and isotopic characterization of biogenic CO2 sources and variability in the Weyburn injection area

► This MMV study captures a rare multi-season and multi-site snapshot of natural variability in soil gases, isotopes, and surface flux. ► We introduce signal-to-noise ratio (SNR) as a useful metric for inter-comparing and selecting monitoring techniques. ► Radiocarbon held the most promise for use as a marker of seepage, with the highest SNR. ► Though commonly considered a useful indicator of seepage, δ13CO2 had the lowest SNR and showed little promise for use at Weyburn. ► Modeling of biological variability proved to be a cheap and effective way of reducing uncertainty, and improving SNR.