Condensation corrosion alters the oxygen and carbon isotope ratios of speleothem and limestone surfaces

• Condensation corrosion is detected using stable isotope analysis of calcite surfaces. • Dissolution and recrystallization cause distinct changes in c and o isotope ratios. • Negative isotope correlation from degassing (higher δ 13 C) and condensation (lower δ 18 O). • Results are consistent with high-resolution studies of speleothem hiatuses. • A new approach to the detection of condensation corrosion in managed caves. Condensation corrosion is a natural process which enhances the chemical weathering of limestone cave chambers and speleothems. We evaluated the use of carbonate tablets for detecting condensation corrosion in Glowworm Cave, New Zealand, using local limestone and speleothem as experimental substrates (herein tablets ). Evidence for condensation corrosion was assessed via three methods: gravimetric (mass wasting), microscopic (surface pitting, recrystallization) and isotopic (δ 13 C and δ 18 O changes). Our results show little evidence of tablet mass loss throughout a 6-month deployment period. However, SEM imaging and isotope analysis (δ 13 C and δ 18 O) of the upper ~50 μm layer of the tablets, suggest that condensation corrosion operates in the cave, especially in sectors affected by large diurnal microclimate variations. Most notably, condensation water altered the tablet surface δ 13 C and δ 18 O values. Small, positive shifts in surface δ 13 C and δ 18 O values are considered to reflect pure dissolution (where dissolution favours the removal of lighter isotopologues). In contrast, tablets that exhibited large positive shifts in δ 13 C in tandem with large negative shifts in δ 18 O values, are interpreted as showing calcite recrystallization and the inheritance of higher DIC δ 13 C values ( 13 C fractionation by CO 2 degassing), lighter water δ 18 O values and/or kinetic fractionation of δ 18 O. This study therefore demonstrates that stable isotopes could be applied to detect paleoclimatic episodes of condensation corrosion in speleothems.