Articles | Volume 21, issue 10
Hydrol. Earth Syst. Sci., 21, 5357–5373, 2017
Hydrol. Earth Syst. Sci., 21, 5357–5373, 2017

Research article 26 Oct 2017

Research article | 26 Oct 2017

Transfer of environmental signals from the surface to the underground at Ascunsă Cave, Romania

Virgil Drăguşin1, Sorin Balan2, Dominique Blamart3, Ferenc Lázár Forray4, Constantin Marin1, Ionuţ Mirea1,4, Viorica Nagavciuc5, Iancu Orăşeanu6, Aurel Perşoiu5,7, Laura Tîrlă8, Alin Tudorache1, and Marius Vlaicu1 Virgil Drăguşin et al.
  • 1Emil Racoviţă Institute of Speleology, Frumoasă 31, 010986, Romania
  • 2National Research and Development Institute for Marine Geology and Geoecology, Mamaia 304, Constanţa, 900581, Romania
  • 3Laboratoire des Sciences du Climat et de l'Environnement LSCE-IPSL CEA-CNRS-UVSQ, Paris-Saclay, Avenue de la Terrasse, Bât. 12, 91198 Gif-sur-Yvette CEDEX, France
  • 4Department of Geology, Babeş-Bolyai University, Kogălniceanu 1, 400084 Cluj-Napoca, Romania
  • 5Stable Isotope Laboratory, Ştefan cel Mare University, Universităţii 13, Suceava 720229, Romania
  • 6Romanian Association of Hydrogeologists, Traian Vuia 6, Bucharest 020956, Romania
  • 7Emil Racoviţă Institute of Speleology, Clinicilor 5, Cluj Napoca 400006, Romania
  • 8Faculty of Geography, University of Bucharest, N. Bălcescu 1, Romania

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.