[M-IS24] Biogeosciences of cold seeps, mud volcanoes, and hydrothermal vents

[MIS24-03] Preliminary report on the survey of submarine mud volcanoes off Tanegashima Island during KS-21-27 cruise

*Akira Ijiri¹, Tomohiro Toki², Masafumi MURAYAMA³, Tatsuhiko Hoshino⁴, Ryoma Setoguchi³, Yuki Mitsutome², Hirotaka Miyamoto³, Koji Tashiro³, Kohma Yasumura², Yudai Kobayashi¹, Kantaro Yamada¹, Yui Yoshizaki¹, Hironori Otsuka¹, Moe Kato⁵ (1.Kobe University, 2.University of the Ryukyus, 3.Kochi University, 4.JAMSTEC, 5.Kanazawa University)

Keywords:Submarine mud volcano, Off Tanegashima Island

Submarine mud volcanoes occur along the margins of convergent plates and are formed by the vertical intrusion of low density, deformable sediments from the deep subsurface to the seafloor. These migration pathways supplies subsurface-derived water, gaseous compounds such as methane, and even microbes to the overlying hydrosphere. In particular, methane emission from mud volcanoes is a significant source of fossil methane to atmosphere or hydrosphere. Around Japan, the Kumano forearc basin and off Tanegashima Island have been known as mud volcano fields. Several tens of mud volcanoes have been found off Tanegashima Island along the Ryukyu Trench. We surveyed three mud volcanoes, MV#8 (30º45´N, 131º36´E), MV#10 (30º23´N, 131º24´E), and MV#15 (31º03´N, 131º40´E), in this area during KS-21-27 cruise from December 2021 to January 2022 by R/V Shinsei-Maru. Our objectives for this cruise are 1) to investigate the activity of mud volcanoes off Tanegashima and clarify the relationship between mud volcano activity and the tectonic environment, and 2) to estimate the flux of carbon and microorganisms released from the mud volcanoes, and to clarify the impact of mud volcanism on the biogeochemical cycle in the ocean. To achieve the objectives, we obtained sediment cores from the summits, and seawater samples from the water column above these mud volcanoes. At MV#15, we succeeded in collecting methane hydrate in the sediment core sample. We present the preliminary report of this cruise including the result of chemical analysis of the methane hydrate sample.