Figure 6

A Keeling plot of δ¹³C – CO₂ vs 1/CO₂ from Flitch of Bacon. for two time periods; autumn 5/3/15–18/4/15, least squares line fit (red), n = 935 and winter 30/6/15–17/7/15, least squares line fit (blue), n = 358. Data points are colour coded to represent air-flow direction and velocity. The Keeling plot intercept provides the δ¹³C – CO₂ of the CO₂ source component mixing with air. The source of high CO₂ in LKB during autumnal (April) bi-directional airflow has δ¹³C – CO₂ = −24.8‰ VPDB. The source of cave CO₂ during winter with near uni-directional airflow has δ¹³C – CO₂ = −19.5‰ VPDB, representing speleothem growth CO₂ degassing within the Cave (δ¹³C drip water ⁻HCO₃ (aq) −10.0‰ + fractionation^{16 −}HCO₃ (aq) - CO₂ (g) at 11 °C −9.48‰ = −19.5‰ VPDB).