Carbon dioxide emissions from soils at Hakkoda, north Japan

A soil gas and CO₂ efflux survey was carried out at Hakkoda, north Japan, to investigate the spatial distribution and origin of the gas which caused the accidental death of three Japanese soldiers on 12 July 1997. In the study area, no fumarolic and/or thermal activity is observed. Chemical composition of the gas from areas with high CO₂ effluxes (>5,000 g m^-2 d^-1) and high CO₂ contents (>15 vol %) indicate a strong deep sourced contribution for CO₂, whereas air and/or air saturated water is suggested for the rest of the discharged gases, which are mainly released from a shallow aquifer. Isotopic analysis of soil gas and hot spring discharges suggests a combination of magmatic degassing and thermal decarbonation, with magmatic degassing being the main contributior to the high CO₂ emission. Approximately 74 t d^-1 of deep-seated (magmatic plus thermal decarbonation origin) CO₂ were estimated to contribute to the total output of CO₂ from this area.