Geochemical Fingerprinting of Rising Deep Endogenous Gases in an Active Hypogenic Karst System

Figure 8

Keeling plots of δ¹³C_CH4 and δ²H_CH4 from cave air. The open circles represent cave air samples, and crosses represent the outdoor atmosphere. The Keeling plot of δ¹³C_CH4 was made with the entire set of air samples collected throughout the eight field campaigns, whereas the δ²H_CH4-Keeling was plotted with the measurements obtained during the last two field campaigns. The vertical dotted arrows indicate the isotopic compositions (δ¹³C_CH4 and δ²H_CH4) for the source of CH₄ that has been added to the cave air to produce the composition observed at each point.