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| Titel |
Assessment of aerodynamic processes on subsurface in karst terrains by rapid multi-parametric surveys (case of Castanar Cave, Spain) |
| VerfasserIn |
A. Fernandez-Cortes, S. Cuezva, M. Garcia-Anton, M. Alvarez-Gallego, J. C. Canaveras, E Porca, V. Jurado, C. Saiz-Jimenez, S. Sanchez-Moral |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250059016
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| Zusammenfassung |
| The transfer of the isotopic signals and the trace element abundances in speleothems
depends of the gas-aqueous-solid equilibrium conditions in the cave environment.
Therefore, the speleothem paleoclimate interpretation requires of a previous knowledge
about the influence of gas exchange and cave ventilation processes on the current
speleothem growth, among other hydrogeochemical features related to the infiltration
process.
Here, we propose an intense and rapid multi-parametric study (few-hours long surveys)
that includes simultaneous and spatial-distributed sampling and measurements of: carrier
(CO2) and trace gases (222Rn and CH4), isotopic signal of CO2 (d13C) and temperature of a
cave atmosphere (Castañar cave, west-central Spain), in order to achieve an early overview
and better understand the relationships between surface weather and the cave microphysical
environment. A portable stable carbon isotope ratio analyzer was used to rapidly and reliably
detect 12CO2 and 13CO2 concentration anomalies and identify possible spatial
changes in the isotopic composition of the cave air in relation to external soil and
atmosphere. Additionally, an aerobiological sampling was conducted to quantify
the level of airborne microorganisms (bacteria and fungi) in cave air. The spatial
distribution of these microenvironmental parameters was modeled by geostatistical
techniques.
Previous studies revealed that Castañar is a low-energy cave characterized by a very
stable microclimate over an annual cycle; however a preferential cave area was
identified due to soft but anomalous variations of the measured parameters. Despite it
is a deep area, far from the single and most elevated entrance of the cave, some
microenvironmental features at this cave site reveal a high connection degree with the
outer atmosphere: 1) higher air temperature (+0.89oC) and variations (+0.22oC); 2)
lower radon levels (roughly -5000 Bq/m3) and 3) an elevated level of airborne
microorganisms, in relation to nearby emplacements. The homogeneous spatial
distribution of CO2 content (3700-3950 ppm) and d13C signal of cave air at inner areas
(-24.2 to -23.8) suggest the soil (-19.8 to -18.6) as the main CO2 source, even in
the most superficial areas near cave entrance and atmosphere (-9,85 to -11,65). A
mixing model could be inferred with both an active ventilation and gas-exchange
with exterior controlled by the geomorphology at surface and filtering by the soil
membrane.
This methodological approach based on monthly samplings extended over, at least, an
annual cycle could be potentially useful to discriminate or select the speleothems with more
reliable climatic records, i.e.; distinguishing those located in the most microclimatic stable
emplacements that should respond to secular changes on climate, from those exposed to
short-term climatic changes that could be used as geo-indicators of early warning. Moreover,
it provides guidance on conservation strategies of caves such as for the delimitation of
specific and immediate cave protection areas in relation to the surface geomorphology. |
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