[M-IS08] Geopark

[MIS08-06] Biogeochemical Properties of Shallow-water CO₂ seeps in the Himeshima and Showa Iwojima Islands, Japan

★Invited Papers

*Masahiko Fujii¹, Tsuneo Ono², Makoto Yamada³, Manabu Ooue⁴, Takeru Ito⁴, Jen-Han Yang^1,5, Yu Horiuchi⁶, Hisashi Oiwane⁷, Masahide Wakita⁸, Shigeki Wada⁴ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Fisheries Resources Institute, Japan Fisheries Research and Education Agency, 3.Faculty of Economics, Ryukoku University, 4.Shimoda Marine Research Center, University of Tsukuba, 5.Institute of Ocean Technology and Marine Affairs, National Cheng Kung University, Taiwan, 6.Oita Himeshima Geopark Promotion Office, 7.Musuhi Inc., 8.Mutsu Institute for Oceanography, Japan Agency for Marine-Earth Science and Technology)

Keywords:CO2 seep, Ocean acidification, Himeshima Island, Showa Iwojima Island, Geopark

CO₂ seeps are considered to anticipate the future marine environment, which will be a matter of concern if human society does not make efforts to drastically reduce CO₂ emissions in the future. Several shallow-water CO₂ seeps have been discovered in the seas around Japan. As they are located in coastal areas that are familiar and important to human society and are relatively easy to access, studies have been conducted in these shallow-water CO₂ seeps. However, many of the studies have been conducted from the perspective of volcanology. In this study, shallow-water CO₂ seeps around the Himeshima and Showa Iojima Islands, located in Kyushu, Japan, were investigated from the perspective of ocean acidification for the first time. Surveys were conducted after May 2022 on the Himeshima Island and after March 2023 on the Showa Iojima Island. The results of the surveys conducted to date on both islands indicate that the CO₂ concentration in seawater in CO₂ seeps is higher than in non-CO₂ seeps, and there are significant decreases in pH and calcium carbonate saturation state, which are close to the values anticipated to be reached by the end of this century unless anthropogenic CO₂ emissions are significantly reduced. Since these shallow-water CO₂ seeps are located within the Japan Geoparks, they can be positioned in the future not only as subjects of studying biological responses to future climate change but also as fields of study tour and ecotourism from the perspective of geoparks.