[SGC48-P04] Helium and CO2 fluxes in Wakamiko caldera
Keywords:Helium Isotopes, Carbon Dioxide, Hydrothermal Vents
Helium isotopic ratios in both seawater and sediment pore water show a mixture of air saturated seawater (~1Ra) and magma source with ~7Ra. This means the origin of excess helium-3 in bottom water is same as that in sediment. This trend is similar to previous studies in 2010 and 2014, which indicate that hydrothermal activity is stable in this period. The 3He and 4He fluxes derived from this study are 13.7 - 18.4 atoms/cm2s and 1.51 - 1.54 x106 atoms/cm2s, respectively. These estimates reflect background diffusion of helium in the Wakamiko caldera. Measurement of gas composition showed that the pore waters are CO2 rich and stable carbon isotope analysis revealed that the CO2 in the system is a mixture of biogenic sources and magmatic volatiles similar to that of Mt. Sakurajima. Finally, the estimated average magmatic CO2 flux from the submerged caldera is 1.41 x 105 mol/yr.