[A-CG50] Biogeochemical linkages between the surface ocean and atmosphere

[ACG50-P05] Transportation of bromoform derived from macroalgae ~Results of the Shinsei-Maru KS-24-12 cruise~

*Atsushi Ooki¹, Masato Deguchi¹, Urumu Tsunogai², Fumiko Nakagawa², Yoko Iwamoto³ (1.Hokkaido University, 2.Nagoya University, 3.Hiroshima University)

Keywords:Halocarbon, Macro algae, Blue carbon

In July 2024, we conducted shipboard observation off the coast of Chiba Prefecture (depth 30 – 54 m) by Shinsei-maru KS-24-12 cruise. Water at depths of 5, 10, 15, 20, bottom -5 m were collected with CTD observations, and the concentrations of volatile organic compounds (VOCs) were measured. The average concentrations of bromoform (CHBr3) at all depths of seven stations were 54 pmol/L, the highest and lowest concentrations were 465 pmol/L and 4.7 pmol/L, respectively. This average concentration was close to the annual average concentration of 52 pmol/L at the center of the Funka Bay, Hokkaido, Japan (Ooki et al., 2013). The measured highest concentration was close to the average of 500 pmol/L along the coast of the Funka Bay in June, where macroalgae flourish, and the measured lowest concentration was close to the concentration of 5.4 pmol/L in the open ocean of North Pacific near Japan (Kurihara et al., 2010). The highest concentrations of bromoform were found in low-salinity water at the surface (5 m) at each station. It is expected that we can use bromoform as a chemical tracer of seashore water affected by macro-algae and that it would be useful to analyze the carbon transportation processes derived from macro-algae. In recent years, the carbon sequestration effect (blue carbon) by marine plants has been attracting attention, and the carbon sequestration effect by macroalgae (macroalgae blue carbon) is expected. For elucidating the process of macro-algae blue carbon, it is expected that bromoform will be used as a good chemical tracer to trace the organic carbon derived from macro-algae.