Abstract
Abstract. We present here the results of a 4-year environmental monitoring program at Ascunsă Cave (southwestern Romania) designed to help us understand how climate information is transferred through the karst system and archived by speleothems. The air temperature inside the cave is around 7 °C, with slight differences between the upper and lower parts of the main passage. CO2 concentrations in cave air have a seasonal signal, with summer minima and winter maxima. These might indicate the existence of an organic matter reservoir deep within the epikarst that continues to decompose over the winter, and CO2 concentrations are possibly modulated by seasonal differences in cave ventilation. The maximum values of CO2 show a rise after the summer of 2014, from around 2000 to about 3500 ppm, following a rise in surface temperature. Using two newly designed types of water–air equilibrators, we were able to determine the concentration of CO2 dissolved in drip water by measuring its concentration in the equilibrator headspace and then using Henry's law to calculate its concentration in water. This method opens the possibility of continuous data logging using infrared technology, without the need for costly and less reliable chemical determinations. The local meteoric water line (δ2H = 7.7 δ18O + 10.1), constructed using monthly aggregated rainfall samples, is similar to the global one, revealing the Atlantic as the strongly dominant vapor source. The deuterium excess values, as high as 17 ‰, indicate that precipitation has an important evaporative component, possibly given by moisture recycling over the European continent. The variability of stable isotopes in drip water is similar at all points inside the cave, suggesting that the monitored drip sites are draining a homogenous reservoir. Drip rates, as well as stable isotopes, indicate that the transfer time of water from the surface is on the order of a few days.
Highlights
The large-scale monitoring of karst systems is mainly undertaken from the perspective of water resource management or conservation (e.g., White, 1988; Ford and Williams, 2013)
Using temperature values from the European Climate Assessment (ECA; Klein Tank et al, 2002) for DrobetaTurnu Severin meteorological station, we see that temperature variability in our area was similar to the regional one (Fig. 4)
We presented here the characteristics of a series of chemical and physical parameters recorded in air, water and modern calcite at Ascunsaand Isverna caves, as a prerequisite for speleothem paleoclimate proxy calibration
Summary
The large-scale monitoring of karst systems is mainly undertaken from the perspective of water resource management or conservation (e.g., White, 1988; Ford and Williams, 2013). Dragusin et al.: Transfer of environmental signals by-case calibration of speleothem proxies against climate parameters and were employed throughout the world: Gibraltar (Mattey et al, 2008), Belgium (Verheyden et al, 2008; Van Rampelbergh et al, 2014), France (Genty et al, 2014), the Czech Republic (Faimon et al, 2012), Spain (Smith et al, 2016; Dumitru et al, 2017), Austria (Spötl et al, 2005), Germany (Riechelmann et al, 2013), USA (Onac et al, 2008; Feng et al, 2014; Meyer at al., 2014), Australia (Jex et al, 2012) or China (Hu et al, 2008; Duan et al, 2016) Such studies focus mainly on parameters such as cave air temperature and relative humidity, CO2 concentration in drip water and cave atmosphere, or stable isotope ratios in drip water and modern calcite. A series of review papers have detailed the systematics of stable isotopes in speleothems (McDermott, 2004; Fairchild et al, 2006; Lachniet, 2009), while the book of Fairchild and Baker (2012) offers an updated and detailed framework for speleothem paleoclimatology
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