Analysis of Cave Sediments at Three South Central Texas Caves: Potential Implications for Cave-Air CO2 Production

Robber Baron Cave, a small maze cave, located in south-central Texas, exhibits anomalously high CO₂ levels in the summer months. Other caves in the region, Natural Bridge Caverns-north, and Cave Without A Name, yield substantially lower CO₂ concentrations. Analysis of cave sediment δ¹³C and δ¹⁵N values, inorganic geochemistry, and mineralogy suggest microbial activity may contribute to the differences in cave-air CO2 concentrations found in south central Texas caves. Light δ¹³C and δ¹⁵N values, elevated iron and manganese concentrations, and high abundances of goethite, birnessite, and todorokite recorded in elevated shelf deposits in Robber Baron Cave may suggest chemoautotrophic microbial activity. In contrast, cave sediments collected from Natural Bridge Caverns-north and Cave Without A Name show no such evidence. While the respiration from microbial activity is likely a potential source for CO₂ in Robber Baron Cave, there are likely multiple sources and processes that contribute to the elevated CO₂ levels. The analysis of cave sediments from the three caves in this study provides insight into the processes and sources associated with CO₂ production.