We investigate the degassing activity of an active submarine crater, Wakamiko, and an active sub-aerial volcano, Sakurajima, both located in Aira caldera, southern Kyushu, Japan. We provide 3 He/ 4 He, δ 13 C–CO 2 and δ 15 N data for 15 hot springs, wells and bubbling gas from Sakurajima volcano, along with 3 He/ 4 He from seawater at four different sites for both Kagoshima bay and Wakamiko crater. We find a common magmatic 3 He/ 4 He ratio for Sakurajima and Wakamiko, 7.2±0.8 Ra, which is consistent with 1) a mixing between air-saturated water (ASW) and MORB-type He, and 2) a common magmatic source located in the center of Aira caldera. Corrected 3 He/ 4 He, δ 13 C–CO 2 and CH 4 / 3 He data for Sakurajima are correlated with the distance from the volcanic vent (Showa crater), which we attribute to crustal contamination and biogenic reaction. The low δ 13 C–CO 2 values (−10.1±0.2‰ to −13.7±0.3‰) observed at Sakurajima may result from the addition of carbon from organic matter from basement rocks in magmatic source. After correction for air-derived nitrogen, we find δ 15 N c values range between −1.7‰ and +4.3‰ which indicates that magmatic N is dominated by a sedimentary-derived component (up to 65.8%). We calculate Wakamiko fluxes of 4 He (975±228mol/y), 3 He (0.011±0.003mol/y), CO 2 (184±43t/d), and heat (195±22MW). Our helium and heat fluxes are the first in situ fluxes ever reported for Wakamiko crater. All these Wakamiko fluxes are at least one order of magnitude lower than those observed for Sakurajima (CO 2 : 1800t/d; 3 He: 0.71mol/y; heat: 2100MW): degassing at Sakurajima volcano is much stronger than that at Wakamiko crater. The variation of Sakurajima CO 2 flux with time, source (Minamidake or Showa crater) and eruptive activity, appears not to significantly affect the CO 2 flux at Wakamiko crater, which is much more stable (132–307t/d) during the last 30years. This indicates that there is no link between Sakurajima and Wakamiko degassing activity, despite having the same magmatic source.