9:15 AM - 9:30 AM
[MIS11-07] Eighth Wonder of the Oita Himeshima Geopark?: What the CO2 seep tells us
Keywords:Oita Himeshima Geopark, CO2 seep/vent, Ocean acidification
Himeshima Island is a remote island with a circumference of 17 km located in the north of Kunisaki Peninsula in Oita Prefecture, at the western end of the Seto Inland Sea. In 2013, Himeshima was registered as a Japan Geopark under the theme of "a mysterious island created by a volcano”. There are many legends about Himeshima Island, and among them, the Seven Wonders of Himeshima Island have become a tourist resource. Many of these legends are closely related to the volcanic activities of the island.
It has long been known locally that gases are gushing from the seafloor in some areas along the coasts of Himeshima Island. The oceanic CO2 seep/vent areas are considered to anticipate the marine environment that will become a concern in the future unless human society does not make efforts to drastically reduce CO2 emissions. From the viewpoint of marine science, especially ocean acidification research, it is necessary to conduct research on CO2 seep/vent areas, and studies on these areas are being vigorously conducted both domestically and internationally. In Japan, several CO2 seep/vent areas have been found, including Iwotorishima Island in Okinawa Prefecture (Inoue et al., 2013) and Shikinejima Island in Tokyo (Agostini et al., 2015), where research has been conducted from the perspective of ocean acidification. However, those CO2 seep/vent areas found in Japan so far belong to the subtropical or temperate-subtropical transitional zones. Therefore, we started a marine survey in the oceanic CO2 seep/vent area along Himeshima Island in 2022 because it is located in the temperate zone and is considered to be academically and socially significant to investigate different biota from the subtropical zone.
Surveys were conducted in May, July, and December 2022 and January and February 2023. The results of the surveys conducted so far in the two CO2 seep/vent areas at the eastern and western ends of Himeshima show that the pH and calcium carbonate saturation state were significantly low due to the high CO2 concentration in the seawater compared to other areas, and that the values were as low as those anticipated by the end of this century without a significant reduction in anthropogenic CO2 emissions. We are currently analyzing the actual effects of such an ocean environment on marine ecosystems, and will present detailed results at the presentation. The CO2 seep/vent area along the coast of Himeshima Island is located in a relatively accessible shallow-water area, and is expected to be positioned as an interesting attraction not only for academic research but also from the Geopark's viewpoint.
It has long been known locally that gases are gushing from the seafloor in some areas along the coasts of Himeshima Island. The oceanic CO2 seep/vent areas are considered to anticipate the marine environment that will become a concern in the future unless human society does not make efforts to drastically reduce CO2 emissions. From the viewpoint of marine science, especially ocean acidification research, it is necessary to conduct research on CO2 seep/vent areas, and studies on these areas are being vigorously conducted both domestically and internationally. In Japan, several CO2 seep/vent areas have been found, including Iwotorishima Island in Okinawa Prefecture (Inoue et al., 2013) and Shikinejima Island in Tokyo (Agostini et al., 2015), where research has been conducted from the perspective of ocean acidification. However, those CO2 seep/vent areas found in Japan so far belong to the subtropical or temperate-subtropical transitional zones. Therefore, we started a marine survey in the oceanic CO2 seep/vent area along Himeshima Island in 2022 because it is located in the temperate zone and is considered to be academically and socially significant to investigate different biota from the subtropical zone.
Surveys were conducted in May, July, and December 2022 and January and February 2023. The results of the surveys conducted so far in the two CO2 seep/vent areas at the eastern and western ends of Himeshima show that the pH and calcium carbonate saturation state were significantly low due to the high CO2 concentration in the seawater compared to other areas, and that the values were as low as those anticipated by the end of this century without a significant reduction in anthropogenic CO2 emissions. We are currently analyzing the actual effects of such an ocean environment on marine ecosystems, and will present detailed results at the presentation. The CO2 seep/vent area along the coast of Himeshima Island is located in a relatively accessible shallow-water area, and is expected to be positioned as an interesting attraction not only for academic research but also from the Geopark's viewpoint.