UNDERSTANDING THE VARIABILITY IN RADON AND CARBON DIOXIDE CONCENTRATIONS OF CARLSBAD CAVERN

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, which is driven by weather changes on the surface, provides an important control of the cave environment by influencing gas transport as gas concentrations vary rapidly over time with changes in cave ventilation patterns. Understanding how these gases vary with time and location within caves is crucial to quantifying and limiting human exposure. Carlsbad Cavern is an ideal study site as the cave exhibits two different airflow mechanisms: 1) barometric airflow, which is driven by barometric pressure, and 2) circulating convective airflow, which is only present during winter months as it is driven by colder surface temperatures. To obtain information about ventilation pathways, we are simultaneously measuring radon and CO₂ concentrations at high time resolution along with other atmospheric characteristics that directly affect gas transport such as airflow velocity, barometric pressure, temperature, and relative humidity at six sites within Carlsbad Cavern. 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.