Drip water electrical conductivity as an indicator of cave ventilation at the event scale

Abstract

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...

North Atlantic forcing of moisture delivery to Europe throughout the Holocene

“…The two speleothems used in this study (ASR and ASM) grew just 5 m apart, in the Cueva de Asiul system in a stable cave environment (air temp 13.7 ± 0.5 °C) 19 31 (75 m in length, 40 m rock overburden) and were both actively depositing calcite at the time of removal. The cave’s hydrological system is recharged primarily by winter rainfall (1400 mm/year), resulting in cave drip waters that reflect a bulk winter rainfall δ 18 O composition from the preceding year 19 .…”

Low-Calcium Cave Dripwaters in a High CO2 Environment: Formation and Development of Corrosion Cups in Postojna Cave, Slovenia

“…Seasonal cave ventilation, driven by the chimney effect, controls the temporal dynamics of pCO 2 in the cave air [15]. The clearest link between pCO 2 in the cave air and water chemistry comes from records of the SEC (as explored in detail in Reference [59]). The continuous time series of the SEC measured in the RD Cond.…”

Contemporary systematics of vadose zone nitrate capture by speleothem carbonate

“…It is located within the Riaño valley, 21 km south east of Santander, forming part of a connected network of caves which link to those of the neighbouring Matienzo depression (eg. Smith et al, 2015Smith et al, , 2016a. The cave is developed in Lower Cretaceous (Aptian-Albian) carbonate of shallow water platform origin (Dewitt et al, 2014;Aranburu et al, 2015), with host bedrock comprising a mixed calcitedolomite composition (70% dolomite content calculated following , interbedded with sandstones and marl (Gutiérrez, 2010).…”