The use of speleothems to reconstruct past climatic and environmental change through chemical proxies is becoming increasingly common. Speleothem chemistry is controlled by hydrological and atmospheric processes which vary over seasonal time scales. However, as many reconstructions using speleothem carbonate are now endeavouring to acquire information about precipitation and temperature dynamics at a scale that can capture short term hydrological events, our understanding of within cave processes must match this resolution. Monitoring within Cueva de Asiul (N. Spain) has identified rapid (hourly resolution) changes in drip water electrical conductivity (EC), which is regulated by the pCO 2 in the cave air. Drip water EC is therefore controlled by different modes of cave ventilation. In Cueva de Asiul a combination of density differences, and external pressure changes control ventilation patterns. Density driven changes in cave ventilation occur on a diurnal scale at this site irrespective of season, driven by fluctuations in external temperature across the cave internal temperature threshold. As external temperatures drop below those within the cave low pCO 2 external air enters the void, facilitating the deposition of speleothem carbonate and causing a reduction in measured drip water EC. Additionally, decreases in external pressure related to storm activity act as a secondary ventilation mechanism. Reductions in external air pressure cause a drop in cave air pressure, enhancing karst air draw down, increasing the pCO 2 of the cave and therefore the EC measured within drip waters. EC thereby serves as a first order indicator of cave ventilation, 2 regardless of changes in speleothem drip rates and karst hydrological conditions. High resolution monitoring of cave drip water electrical conductivity reveals the highly sensitive nature of ventilation dynamics within cave environments, and highlights the importance of this for understanding trace element incorporation into speleothem carbonate at the event scale.Keywords: Northern Spain; Cueva de Asiul; speleothem; cave ventilation; cave water chemistry; electrical conductivity.
IntroductionSpeleothems are important repositories of palaeoclimate information (Fairchild and Baker 2012).Speleothem carbonate chemistry is routinely used to assess large-scale palaeoenvironmental change, as well as offering the ability to identify annual to sub-annual variations in local meteorology (Treble et al., 2003, Wynn et al., 2014 and vegetation dynamics (Borsato et al., 2007; Fairchild et al., 2010).Although there is a wealth of information to be drawn from cave speleothems, interpretation frequently relies upon understanding site specific controls on carbonate deposition (Spotl et al., 2005, Miorandi et al., 2010. For this reason, a greater emphasis is now being placed upon robust high resolution cave monitoring studies, which aid the interpretation of speleothem chemistry through the characterisation of cave environments (Mattey et al., 2010, Wong et al., 2011.Drip wat...