, Auditorium
Understanding how ventilation and sources interact to regulate cave gas concentrations is key to explaining radon and CO2 variability within cave systems, with broader implications for interpreting paleoclimate records, speleogenesis patterns, and human health. Surface weather drives cave air circulation, playing a central role in shaping the cave environment by influencing gas transport.
This study investigates gas dynamics in Carlsbad Cavern, which exhibits two distinct airflow mechanisms: barometric airflow and circulating convective airflow. To investigate how these ventilation processes impact gas dynamics, we measured CO2 and radon concentrations at high temporal resolution alongside airflow velocity, barometric pressure, temperature, and relative humidity at six sites within the cavern. A simple gas transfer model was applied to quantify decreases in CO2 during active convective circulation and evaluate whether it accurately captures gas exchange between the surface and subsurface through a convection cell.
The model reasonably fits the data during the onset of convection, suggesting that gas exchange occurs over a timescale of days, with tourists likely being the main source of CO2. A more isolated cave site yields an exchange timescale of approximately one month. The model was also adapted for radioactive gas transfer and applied to observed radon declines to assess whether it accurately estimates gas exchange via convection. As radon and CO2 originate from different sources, synchronized patterns at a given site, particularly concentration decreases, indicate that ventilation is the primary control over both gases. Divergent patterns indicate the sources of gases are the key driver of concentration variability.
Riannon Colton, Matthew Covington