121-6 Understanding the variability in gas concentrations of Carlsbad Cavern

Session: Caves and Karst Through Space and Time: Biogeochemistry, Climate, and Astrobiology

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Determining how ventilation and sources interact to control cave gas concentrations will allow a better understanding of how radon and CO₂ vary within cave systems, with implications for interpreting paleoclimate records, speleogenesis patterns, and human health. Cave air circulation, driven by surface weather changes, significantly influences the cave environment by affecting gas transport. In this study, we analyze gas dynamics in Carlsbad Cavern, which exhibits two distinct airflow mechanisms: 1) barometric airflow and 2) circulating convective airflow. To investigate ventilation processes and their impact on gas dynamics, we measure CO₂ and radon concentrations at high temporal resolution, along with airflow velocity, barometric pressure, temperature, and relative humidity at six sites within the cavern. We apply a simple gas transfer model to observed decreases in CO₂ during active convective circulation to assess whether it accurately approximates gas exchange between the surface and a large underground volume. The exponential model reasonably fits the data during the onset of convection and suggests gas exchange times between the surface and the main passage are on the order of days, with tourists likely being the main source of CO₂. A more isolated site in the cave shows an exchange timescale of roughly a month. A simple gas transfer model created for radioactive gas transfer was applied to the observed radon declines to assess whether it accurately approximates gas exchange between the surface and a large underground volume via a convection cell. Since the source zones of radon and CO₂ are different, if concentrations of radon and CO₂ follow the same patterns in time at a site, and decreases in concentration coincide with periods of increased surface exchange, then this indicates that the gases are influenced by ventilation from surface air. Alternatively, if CO₂ and radon follow different patterns, then the sources of the gases are an important control on concentrations.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9167

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