 |
| Titel |
Generation and dispersal of carbon dioxide in the caves and karst of Gibraltar |
| VerfasserIn |
T. Atkinson, D. Mattey, J.-P. Latin, M. Ainsworth, R. Durell |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069260
|
|
|
|
|
|
| Zusammenfassung |
| The gases in the soil, in caves and in the smaller voids of the vadose zone in karstic
limestones are all generally enriched in CO2 relative to open atmosphere. The concentrations
and fluxes of CO2 in cave air have a close relationship with the deposition of speleothem
calcite but there are still very few detailed studies that trace the generation and dispersal of
CO2 in whole karst systems, i.e. as a gas and in dissolved form within a linked system
comprising soil, caves and the vadose zone. The Rock of Gibraltar forms a N-S trending ridge
2.5 km long within which solution caves are present at altitudes extending from below sea
level to over 300m asl. Cave monitoring has been carried out since 2004 and focuses on
two cave systems: St Michaels Cave (SMC) located near the top of the rock at
275m asl and Ragged Staff Cave located in the heart of the rock near sea level.
Monthly sampling and analysis of air and water combined with continuous logging of
temperature, humidity and drip discharge rates reveals the importance of density-driven
seasonal ventilation which drives large-scale advection of CO2-rich air though the cave
systems. Advective flow is upwards during winter months, resulting in low pCO2 at
sea level and high pCO2 in caves near the top of the rock and the flow reverses in
summer, ventilating high-level caves and raising cave air pCO2 at lower altitudes. In
this talk we focus on geochemical tracing of CO2 generation and dispersal using
the abundance and carbon isotopic compositions of gaseous CO2 and dissolved
inorganic carbon (DIC). The results of a four-year study at SMC are not consistent
with the generally accepted view that CO2in cave air originates by degassing of
dripwater that has acquired CO2primarily from the soil zone. We demonstrate the
importance of deep vadose zone air as a source of CO2 in karst systems and show that in
St. Michaels Cave the abundance and isotopic composition of CO2 of the cave
atmosphere is primarily controlled by mixing between a CO2– rich vadose air component
and background atmospheric air introduced into the cave by seasonal ventilation. |
|
|
|
|
|
|