Table 1 Summary of trace gases in Chifley Cave, measured in Lower Katies Bower during two typical weeks in summer and winter.

Chifley Cave	Lower Katies Bower		week	5/3/15–12/3/15	Winter	Winter	week	30/6/15–7/7/15
	Summer	Summer	Summer	Summer change	Winter	Winter	Winter	Winter change
	MIN	MAX	AVERAGE	cave–ambient	MIN	MAX	AVERAGE	cave–ambient
CH₄ ±20 ppb	−2	21	11	>99% depletion	556	1,147	981	55% depletion
CO₂ ±5 ppm	4,014	8,463	6,566	>14 × enrichment	446	1,029	568	1.3 × enrichment
δ¹³C–CO₂ ±1‰ PDB	−24.9	−23.2	−24.2	−14.1‰ difference	−16.2	−9.9	−11.8	−2.7‰ difference
N₂O ±5 ppb	659	1,196	989	3 × enrichment	328	331	329	no difference
CO ±5 ppb	−3	0	−2	>99% depletion	0	86	5	>90% depletion
Rn ±25 Bq m⁻³	3,264	13,824	9,999	>500 × enrichment	133	408	203	>10 × enrichment
Cave temperature	13.0	13.6	13.5	4.4 °C cooler	11.0	12.5	12.1	8.5 °C warmer
External temperature	7.4	29.1	17.8		−3.7	14.3	3.6
Air-flow m s⁻¹	−0.919	0.140	−0.027		−0.127	0.302	0.095

A week is approximately the duration of a single synoptic cycle where the external temperature range and pressure remain stable causing a pattern of cave ventilation air-flow typical of the season. The change in the cave environment is relative to the synchronous trace gas measurement of the external ambient atmosphere using 8-minute averages taken hourly and averaged over approximately a week. Weekly averaging removes the diurnal cycle (MIN & MAX) from the reported change between cave and ambient atmospheres. There is a marked seasonal difference in the magnitude of depletion or enrichment for each trace gas reflecting the dominant air-flow direction with different sources of trace gases (Summer – soil & external ambient air, Winter – external ambient air). Comparison of weekly average cave temperature to weekly average external temperature differs in sign and magnitude seasonally. The difference in temperature between cave and ambient causes the seasonal reversal of dominant air-flow with consequent winter seasonal bias in average air-flow velocity and air-mass ventilated through the cave. Doubling the temperature difference has caused a trebling of average air-flow velocities.

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