[A-CG41] Coastal Ecosystems 2. Coral reefs, seagrass and macroalgal beds, and mangroves

[ACG41-09] Inorganic carbon cycle in mangrove soils and possibility for assimilation of outwelled mangrove carbon in seagrass and coral ecosystems

*Wataru Nakamura¹, Kojin Tsuchiya¹, Toshihiro Miyajima¹, Yosuke Miyairi¹, Yusuke Yokoyama¹, Kenta Watanabe², Kei Gempei², Tomohiro Kuwae², Jun Sasaki¹ (1.The University of Tokyo, 2.Port and Airport Research Institute)

Keywords:Radiocarbon isotope, Dissolved Inorganic Carbon, Total Alkalinity, CO2 flux, Stable isotope, Mangrove

Although mangrove habitats are limited in sub-tropical and tropical areas, mangrove ecosystems account for approximately 15% of annually buried carbon in the ocean. They play an important role as blue carbon ecosystems that take up atmospheric CO₂. It is also known that plenty of dissolved inorganic carbon (DIC) is outwelled to associated seagrass beds and coral reefs during an ebb tide. However, the biogeochemical mechanisms, such as the dominant mineralization process that occurs in mangrove soils through tidal interactions, remain uncertain. Additionally, the fate of DIC outwelled from mangrove ecosystems has yet to be fully studied.
In order to address these questions, a field observation was conducted in the estuary of the Fukido River on Ishigaki Island, Okinawa, Japan. This presentation will primarily report on three key findings: (1) the results of the measured CO₂ and DIC flux among soil, water, and the atmosphere, with the hypothesis that the CO₂ flux from soil to the atmosphere is much higher than the CO₂ flux from water to the atmosphere; (2) the results of the vertical profiles of carbonate chemistry parameters (total alkalinity, pH, DIC, and δ13C-DIC) in mangrove soil between inundation and exposed periods, with the hypothesis that the dominant mineralization process changes between these periods; and (3) the results of the radiocarbon isotope ratio measurements in outwelled mangrove waters, offshore waters, seagrass, and reef building coral, with the hypothesis that outwelled DIC from mangrove soil is assimilated in other blue carbon ecosystems within the estuary of the Fukido River.