IDENTIFYING GEOTHERMAL ACTIVITY IN LOW CO2 FLUX GEOTHERMAL SYSTEMS

Carbon dioxide flux is a widely applied tracer in geothermal and volcanic systems with elevated gaseous emissions at the surface. In an effort to explore the potential of this tracer in relatively low, diffused CO₂ systems we completed a survey in the Ngatamariki geothermal field (Taupo Volcanic Zone, NZ). Our results show: (1) CO₂ fluxes between 0.247 and 217 gCO₂m^-2day^-1, (2) 10 cm depth temperatures ranging between 12.9 to 50.4 °C, and (3) δ¹³C of CO₂ values of these gases have a range of -26 to -7.3 ‰. Of the 320 measurements 94% of the soil CO₂ flux measurements fall below the previously established background of 90 gCO₂m^-2day^-1 and 5.6% of the soil temperatures are greater than 30°C. No significant correlation between increasing soil temperature and CO₂ flux is present. The greatest diffuse soil CO₂ flux recorded in the Ngatamariki field is associated with an area of recent land disturbance rather than the active thermal features. By coupling δ¹³C of CO₂ and CO₂ concentration we were capable of indentifying both active thermal areas at Ngatamariki despite their low CO₂ flux. Our findings demonstrate the importance of utilizing diffuse soil gas investigations and high spatial density δ¹³C of CO₂ surveys to identify blind geothermal resource targets in low CO₂ flux systems.