Figure 4

Late summer time series of CO, CO₂, Rn, N₂O, and δ¹³C – CO₂ from Lower Katies Bower corresponding with correlation plots (5/3/15–18/4/15). CO is totally depleted (measurement error ± 5 ppb) within Chifley Cave relative to a variable background ambient concentration of 75–110 ppb. CO depletion is not seasonally variable. Rn, N₂O and δ¹³C – CO₂ (−24.8‰ VPDB) gas tracers each correlate strongly with CO₂ and identify karst soil overlying Chifley Cave as the only likely source of high CO₂ in the cave in summer (Figs 1 and 2). Late summer bi-directional air-flow shows large synchronous fluctuations in CO₂ and gas tracers.