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Subterranean sinks and sources of greenhouse gases

Climate change is inextricably linked to the carbon cycle and natural and/or induced variations in the concentration of greenhouse gases (GHGs) in the atmosphere. Recent research has indicated that the microclimates and geochemistry of subterranean karst environments can act as sinks during cold periods and as sources during warmer periods.
Subterranean sinks and sources of greenhouse gases
One of the greatest challenges currently facing climate scientists is to identify and characterise all the possible sources, reservoirs and sinks of greenhouse gases (GHG). This information will enable them to more accurately calculate the carbon GHG budget, as subterranean atmosphere are key locations that need to be considered regarding the balance of atmospheric carbon.

The aim of the SMACKS (Sourcing methane and carbon dioxide in karst systems) project was to study the dynamics of the main GHGs, carbon dioxide (CO2) and methane (CH4), in natural underground environments of karst terrain. The work included identifying and quantifying their role in the carbon budget of terrestrial ecosystems.

Real-time isotope tracing was used to identify the environmental factors controlling CO2 and CH4 exchanges between the atmosphere and subterranean environments at karst locations. A karst landscape is formed from the dissolution of soluble rocks such as limestone and gypsum and features underground drainage systems with sinkholes and caves. Hence, the field sites included the Ojo Guareña karst system in Spain, one of the longest cave systems in Europe.

A multidisciplinary studied approach was applied to the study of cave microclimates. Researchers also investigated infiltration water as a mechanism for transporting gases, cave ventilation, water and minerals in soil, and highly weathered carbonate bedrock (epikarst). The results from the monitoring programme and air analyses revealed that the subterranean atmosphere of karst systems could play a role in regulating GHGs in the atmosphere.

SMACKS provided a detailed knowledge of the processes underlying gases emissions or storage in subterranean karst environments with direct connections with the lower troposphere. This is vital to understanding and managing sinks and sources related to this type of terrestrial ecosystem.

The project’s results will lead to improved modelling of feedback between climate, GHGs and carbon exchange in the vadose zone, which lies between the land surface and the water table. This will enable better management of GHG sinks by providing knowledge of the geological storage (or release) capacity of natural ecosystems.

Related information

Keywords

Carbon cycle, karst, SMACKS, carbon dioxide, methane, real-time isotope tracing
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