A high-resolution spatial survey of cave air carbon dioxide concentrations in Scoska Cave (North Yorkshire, UK) :implications for calcite deposition and re-dissolution.

Carbon dioxide concentration variability in caves has implications for palaeoclimatic research involving stalagmites, the conservation of cave art, condensation corrosion, and safety during cave exploration. Here we present a high-resolution spatial survey of cave air carbon dioxide partial pressure (PCO2) in the 1.5km Scoska Cave system in North Yorkshire, UK, constructed using measurements taken during the interval of July 1 – July 5, 2008. According to the spatial PCO2 survey, 76% of the cave air PCO2 increase occurred within the first ~50 metres; consequently the PCO2 gradient throughout the rest of the cave was slight. As is the case in other caves, this suggests that a ‘front’ exists at this site between high PCO2 cave air and low PCO2 outside air, where the PCO2 increases dramatically over a short distance. Temperature data support this interpretation. This CO2 ‘front’ is thought to represent the farthest point reached by large-scale advection of air out of the cave, and its position is hypothesized to fluctuate depending on atmospheric conditions. Thus, distinct PCO2 trends characterize sections of the Scoska Cave system, which result in spatial variability in calcite deposition and redissolution. Modelled stalagmite growth rates vary between negligible and 0.21 mm yr-1, depending on unconstrained drip water [Ca2+] values and cave atmosphere PCO2. Assuming constant drip water [Ca2+], optimum calcite deposition occurs near to the cave entrance, where ventilation and advection reduce PCO2 levels most effectively. However, calcite precipitation on the roof of the cave may partially control the [Ca2+] of drip water that reaches the floor, so although the link between overall calcite deposition (i.e., on the roof and the floor) and PCO2 appears robust, the effect of variable cave air PCO2 on stalagmite growth rates requires more research. These calculations suggest that calcite precipitation rates in different areas of Scoska Cave may differ due to local PCO2 and temperature variability, highlighting the benefits of thoroughly understanding site-specific cave environmental factors prior to the interpretation of stalagmite-based palaeoclimate records.