Japan Geoscience Union Meeting 2016

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Symbol A (Atmospheric and Hydrospheric Sciences) » A-CG Complex & General

[A-CG15] Coastal Ecosystems - 2. Coral reefs, seagrass meadows, and mangroves

Tue. May 24, 2016 1:45 PM - 3:15 PM 301A (3F)

Convener:*Toshihiro Miyajima(Marine Biogeochemistry Group, Division of Ocean-Earth System Science, Atmosphere and Ocean Research Institute, The University of Tokyo), Atsushi Watanabe(Department of Mechanical and Environmental Informatics Graduate School of Information Science and Engineering Tokyo Institute of Technology), Yu Umezawa(Nagasaki University), Chair:Toshihiro Miyajima(Marine Biogeochemistry Group, Division of Ocean-Earth System Science, Atmosphere and Ocean Research Institute, The University of Tokyo), Yoshiyuki TANAKA(Japan Agency for Marine-Earth Science and Technology Mutsu Institute for Oceanography)

2:45 PM - 3:00 PM

[ACG15-05] Total alkalinity flux at seagrass meadow estimated by eddy covariance and pore water profiles in sediment

*Shoji Yamamoto1, Hajime Kayanne1, Chuki Hongo2, Toko Tanaya3, Kenta WATANABE3, Tomohiro Kuwae3 (1.The University of Tokyo, Department of Earth and Planetary Science, 2.University of the Ryukyus, 3.Port and Airport Research Institute)

Keywords:Ocean acidification, Total alkalinity flux, Mg-calcite

Ocean acidification decreases the pH of seawater and the saturation state of minerals, and carbonate sediment dissolution could be more sensitive to ocean acidification than calcification by reef organisms (Eyre et al. 2014). Particularly in seagrass-carbonate sediment, it has been suggested that both abundant labile organic matter and wide redox range would increase pCO2 in sediment, and total alkalinity (AT) flux from sediment to water column caused by Mg-calcite dissolution would also increase. Here, we measured sedimentary dissolved oxygen (DO) and carbonate profiles in a seagrass area of Shiraho coral reef, Ishigaki Island, and AT flux at the sediment-water interface was estimated using eddy covariance (EC). Almost half of the sediment was Mg-calcite derived from foraminifera and its Mg content was 16.4 mol%. Analysis of the sedimentary DO and Oxidation-Reduction Potential (ORP) profiles at night indicated that O2 was depleted deeper than at least 4 mm and sulfate reduction could occur. While pore water AT and dissolved inorganic carbon values increased with depth, pore water saturation state of aragonite was constant at a value of ~ 2.3 during the entire nighttime. On the other hand, the calculated nighttime AT flux from sediment to water column was 0.9–3.2 mmol m-2 hr-1 though seawater in water column was oversaturated with respect to Mg-calcite. This would be caused by Mg-calcite dissolution and bacterial sulfate reduction, and AT flux from sediment to water column would increase further by ocean acidification.