[S-GC37] Volatiles in the Earth - from Surface to Deep Mantle

[SGC37-P05] Seasonal overturn and volcanic emissions in Wakamiko submerged caldera

*Ma Teresa Nakajima¹, Naoto Takahata¹, Hajime Obata¹, Takanori Kagoshima², Yuji Sano³ (1.AORI, University of Tokyo, 2.University of Toyama, 3.Kochi University)

Keywords:Helium Isotopes, Wakamiko Caldera, Submarine Volcanoes

Wakamiko Caldera is an isolated basin located in the northern part of Kagoshima Bay. The underwater caldera is known for the active fumaroles that continuously discharge volcanic substances into the overlying water. Due to the limited exchange of the waters in the caldera with the surrounding, the water column gets stagnant and stratified from spring to autumn. Previous studies have shown that overturning occurs in winter. Based on new data obtained from samples obtained on cruise KH-22-4, we show that during winter, vertical mixing “resets” the helium isotope profile. After winter, as the water column regains back its stratification, fluids with mantle helium slowly builds-up near the seafloor resulting to the high ³He/⁴He ratio previously observed. We now use the difference in ³He/⁴He ratio in different seasons to calculate the flux of ³He. Using this method, we estimate the ³He flux at approximately 0.01 mol/year.