Transfer of environmental signals from surface to the underground at Ascunsă Cave, Romania
Virgil Drăgușin1, Sorin Balan2, Dominique Blamart3, Ferenc L. Forray4, Constantin Marin1, Ionuț Mirea1,4, Viorica Nagavciuc5, Aurel Perșoiu5,6, Laura Tîrlă7, Alin Tudorache1, and Marius Vlaicu11Emil Racoviță Institute of Speleology, Frumoasă St. 31, 010986, Romania 2National Research and Development Institute for Marine Geology and Geoecology, Mamaia Blvd. 304, Constanța, 900581, Romania 3Laboratoire des Sciences du Climat et de l'Environn ement 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, Ștefan cel Mare University, Universității 13, Suceava 720229, Romania 6Emil Racoviță Institute of Speleology, Clinicilor 5, Cluj Napoca 400006, Romania 7Department of Geography, University of Bucharest, N. Bălcescu Street 1, Romania
Received: 25 Nov 2016 – Accepted: 03 Jan 2017 – Published: 04 Jan 2017
Abstract. We present here the results of a four year environmental monitoring program at Ascunsă Cave, Romania, intended to understand how climate information is transferred through the karst system and archived in speleothems. The air temperature inside the cave is around 7 °C, with slight differences between the upper and lower parts of the main passage. Relative humidity measurements were hampered by condensation on the capacitive sensors we used, thus we consider it to be close to 100 %. 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 δ2H excess values, as high as 17 ‰, indicate that precipitation has an important evaporative component, possibly given by moisture recycling over the European continent. CO2 concentrations in cave air have a seasonal signal, with summer minima and winter maxima. This might be indicative of an organic matter reservoir deep within the epikarst that continues to decompose over the winter, possibly modulated by seasonal differences in cave ventilation. The maximum values of CO2 show a rise after the summer of 2014, from around 2000 ppm to about 3500 ppm. An analogous rise is seen in drip water stable isotopes and chemical elements such as Sr and Mg. The variability of stable isotopes and chemical elements is similar at all points inside the cave, indicating that they are draining a homogenous reservoir. Using two newly designed types of water/air equilibrators we were able to determine drip water dissolved CO2, by measuring its concentration in the equilibrator headspace and then using Henry's law to calculate its concentration in water. This opens the possibility of continuous data logging using infrared technology without the need of costly and less reliable chemical determinations.
Drăgușin, V., Balan, S., Blamart, D., Forray, F. L., Marin, C., Mirea, I., Nagavciuc, V., Perșoiu, A., Tîrlă, L., Tudorache, A., and Vlaicu, M.: Transfer of environmental signals from surface to the underground at Ascunsă Cave, Romania, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-625, in review, 2017.