Understanding the dynamics and distribution of CO
2
in the subsurface atmosphere of carbonate karst massifs provides important insights into dissolution and precipitation processes, the role of karst ...systems in the global carbon cycle, and the use of speleothems for paleoclimate reconstructions. We discuss long-term microclimatic observations in a passage of Postojna Cave, Slovenia, focusing on high spatial and temporal variations of
p
CO
2
. We show (1) that the airflow through the massif is determined by the combined action of the chimney effect and external winds and (2) that the relationship between the direction of the airflow, the geometry of the airflow pathways, and the position of the observation point explains the observed variations of
p
CO
2
. Namely, in the terminal chamber of the passage, the
p
CO
2
is low and uniform during updraft, when outside air flows to the site through a system of large open galleries. When the airflow reverses direction to downdraft, the chamber is fed by inlets with diverse flow rates and
p
CO
2
, which enter via small conduits and fractures embedded in a CO
2
-rich vadose zone. If the spatial distribution of inlets and outlets produces minimal mixing between low and high
p
CO
2
inflows, high and persistent gradients in
p
CO
2
are formed. Such is the case in the chamber, where vertical gradients of up to 1000 ppm/m are observed during downdraft. The results presented in this work provide new insights into the dynamics and composition of the subsurface atmosphere and demonstrate the importance of long-term and spatially distributed observations.
•Analysis of gravimetric/hydrologic data to constrain karst system hydrodynamics.•Gravity data modelling requires the integration of the autogenic recharge.•Gravity data sensitive to flow conditions ...in the karst conduits.
In this paper we employ a combination of gravity and hydrologic data to constrain a hydraulic model of the Škocjan Caves, an allogenic dominated karstic system in Slovenia. The gravity time-series recorded by a spring-based gravimeter, are carefully analyzed to remove tidal and non-tidal effects and unveil the local hydrologic contribution, which is influenced by the temporary accumulation of water in the cave system during the flood events of the Reka river.
We make use of a combined analysis of three large flood events with peak river discharge of about 200, 230 and 300 m3/s, that caused significant water level and gravity variations sensed by the pressure transducer and by the gravimeter. By the integration of hydraulic modelling we study the different coupled gravimetric-hydrologic responses to these flood events: we show that, depending on the peak discharge and duration of the event, different flow conditions are present in the cave system. In addition to the information provided by the pressure transducer, the gravimeter is sensitive to the flow dynamics in a different sector of the cave due to the choice of its location; this configuration helps to better constrain the hydraulic model.
Moreover, we find that the autogenic recharge by percolating water can significantly affect the gravity time-series and must be considered in related models. By inclusion of both the hydraulic model outcomes and of the modelling of the autogenic recharge, we are able to better explain the gravity transients during the two smaller magnitude events. In particular, during such events the autogenic contribution produces a transient gravity signal, which is about 4 times larger than the allogenic one, while during the largest flood the allogenic contribution drastically overcomes the autogenic effect by a factor 20.
By discussing this case, we prove the potential of terrestrial gravity observation to depict the hydro-dynamics of these complex karstic systems as well as the potential of gravimetry to remotely monitor these storage units.
Rapid progress, broad and productive collaborations, ever better access to sophisticated research equipment, the need for publishing and the search for funds sometimes distract us from deep thinking ...on the research questions that should be the key element of scientific work. Acta Carsologica has an inherent interest in the research at Classical Karst, where most of our editors work. ...we publish in our journal, but we do not interfere into the editorial process of our manuscripts. In addition to managing reviews and making decisions, the editors' tasks often include providing funds for layout and printing, reporting, website maintenance, proofreading, translation, transport, packaging and dispatch of issues.
An obituary for Andrej Kranjc, the geographer, karstologist, and editor who died on January 7, 2023 at 80-years-old, is presented. Kranjc's passion for caving was awakened as a high school student. ...His journey into caves and karst research began in 1965, as a student of geography and archaeology, he helped organize the International Speleological Congress. This brought him into contact with the researchers at the Karst Research Institute in Postojna and eventually led to him becoming their co-worker. Throughout his academic career, he was guided and inspired by academician Ivan Gams. Kranjc's expertise spanned the entire range of karstology and included speleology, geomorphology, hydrology, terminology and the history of karst research, which he continued to deal with after his retirement.
Monitoring the water movements in karstic areas is a fundamental but
challenging task due to the complexity of the drainage system and the
difficulty in deploying a network of observations. ...Gravimetry offers a valid
complement to classical hydrologic measurements in order to characterize
such systems in which the recharge process causes temporarily accumulation
of large water volumes in the voids of the epi-phreatic system. We show an
innovative integration of gravimetric and hydrologic observations that
constrains a hydrodynamic model of the Škocjan cave system (Slovenia).
We demonstrate how the inclusion of gravity observations improves water mass
budget estimates for the Škocjan area based on hydrological observations
only. Finally, the detectability of water storage variations in other
karstic contexts is discussed with respect to the noise performances of
spring and super-conducting gravimeters.
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