Magda Mandic - Academia.edu (original) (raw)

Uploads

Conference Presentations by Magda Mandic

The formation of speleothems in the cave is a complex geochemical process dependent on various hy... more The formation of speleothems in the cave is a complex geochemical process dependent on various hydrological and environmental conditions. Using stable isotopes as a paleoclimate proxy is a challenge due to the multitude of fractionation processes. It is of utmost importance to understand and possibly quantify mechanisms in the cave that are influencing speleothem precipitation. The environmental process that is considered to be crucial for the equilibrium carbonate precipitation is the spatial and temporal variability of CO 2. To better characterize cave ventilation patterns, monitoring of pCO 2 , δ 13 C and δ 18 O in cave air at high temporal resolution (up to 1 s) was performed in Spannagel Cave, a high-alpine cave system in the Zillertal Alps, Austria. A Thermo Scientific Delta Ray Isotope Ratio Infrared Spectrometer was installed in a chamber ca. 100 m behind the cave entrance. The air temperature was independently monitored inside and outside the cave. The data show two distinct patterns in terms of CO 2 concentration and its isotopic composition, which are closely coupled with the temperature difference between the cave interior and the outside atmosphere. This gradient controls the direction of air flow in the cave on a seasonal to synoptic timescale (chimney-type ventilation). The summer circulation is characterized by CO 2 closely resembling atmospheric values (pCO 2 = 399 ± 12 ppm, δ 13 C =-8.5 ± 0.7‰, δ 18 O = 8.1 ± 2.5 ‰). The winter circulation mode features generally higher CO 2 concentrations and lower isotopic compositions (pCO 2 = 409 ± 14 ppm, δ 13 C =-10.1 ± 0.7 ‰, δ 18 O = 2.3 ± 1.5 ‰). The high temporal resolution of stable isotope data allows tracking cave air ventilation changes, including transient and short-lived ones. Specifically, periods impacted by respiration from cave visitors were filtered based on a linear mixing model.

Papers by Magda Mandic

Postojna Cave (Slovenia) is one of the most famous karst caves in South Eastern Europe. Drip wate... more Postojna Cave (Slovenia) is one of the most famous karst caves in South Eastern Europe. Drip water is one of the factors that determines cave interior. During 2010 and 2011 monitoring of drip water in Postojna Cave was performed at 9 locations within the Cave. Drip rate was measured and the isotopic composition ( 18 O) of drip water was determined. Rain water was collected at Zalog pri Postojni and its  18 O composition determined. Variations in  18 O of drip water range from -8 to -10 ‰. The mean residence time was estimated based on the assumption of complete mixing, and for different drip sites it varies between 7 months and several years.

Partial pressure of CO 2 (pCO 2 ) and its isotopic composition (δ 13 C airCO2 ) were measured in ... more Partial pressure of CO 2 (pCO 2 ) and its isotopic composition (δ 13 C airCO2 ) were measured in Postojnska jama, Slovenia, at 10 locations inside the cave and outside the cave during a one-year period. At all interior locations the pCO 2 was higher and δ 13 C airCO2 lower than in the outside atmosphere. Strong seasonal fluctuations in both parameters were observed at locations deeper in the cave, which are isolated from the cave air circulation. By using a binary mixing model of two sources of CO 2 , one of them being the atmospheric CO 2 , we show that the excess of CO 2 in the cave air has a δ 13 C value of -23.3 ± 0.7 ‰, in reasonable agreement with the previously measured soil-CO 2 δ 13 C values. The stable isotope data suggest that soil CO 2 is brought to the cave by drip water.

International Journal of Speleology, 2010