Spatial and temporal variability in modelled stalagmite growth rates in a medium-length cave system : implications for palaeoclimate research.

The dynamics of CO2 in caves is an important consideration for cave conservation studies (e.g. the conservation of cave art), exploration (e.g. the location and severity of ‘bad air’), and palaeoclimate studies that utilise cave calcite deposits. Recent research suggests that cave air pCO2 levels may influence both the rate and seasonality of speleothem deposition; therefore spatiotemporal variability in pCO2 may have implications for palaeoclimate proxy records derived from stalagmites. Based on a high-resolution spatial survey of cave air pCO2 at Scoska Cave (North Yorkshire, UK), undertaken in 2008, and on calcite growth equations, variations in stalagmite growth rates throughout the cave system can be estimated. The minimum and maximum modelled growth rates are 0.11 and 0.21 mm yr-1, respectively (based on: thin film thickness = 0.1 mm, [Ca2+] = 2.5 mmol L-1, drip interval = 60 s, and kinetic rate constant = 1.28x10-4 mm s-1). Modelling suggests that higher pCO2 levels prevalent in the deeper sections of the cave, or close to sumps, engender the lowest growth rates. Conversely, sections characterised by lower cave air pCO2 are predicted to host faster-growing stalagmites, owing to increased drive for degassing of dissolved CO2 from dripwaters. Moreover, imposing a lower initial dripwater [Ca2+] condition illustrates that calcite dissolution is possible throughout the majority of this cave system. In addition, a 32-day time series of cave air pCO2 allows temporal behaviour in the growth rates of stalagmites to be modelled. This suggests that the δ18O signals of stalagmites growing in spatially-separated sections of this cave system may differ, as a result of cave air pCO2 and growth rate variability.