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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-448
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-448
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 19 Nov 2019

Submitted as: research article | 19 Nov 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Macroalgal metabolism and lateral carbon flows create extended atmospheric CO2 sinks

Kenta Watanabe1, Goro Yoshida2, Masakazu Hori2, Yu Umezawa3, Hirotada Moki1, and Tomohiro Kuwae1 Kenta Watanabe et al.
  • 1Coastal and Estuarine Environment Research Group, Port and Airport Research Institute, 3-1-1 Nagase, Yokosuka 239-0826, Japan
  • 2National Research Institute of Fisheries and Environment of Inland Sea, Japan Fisheries Research and Education Agency, 2-17-5 Maruishi, Hatsukaichi 739-0452, Japan
  • 3Department of Environmental Science on Biosphere, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan

Abstract. Macroalgal beds have drawn attention as one of the vegetated coastal ecosystems that act as atmospheric CO2 sinks. Although macroalgal metabolism as well as inorganic and organic carbon flows are important pathways for CO2 sequestration by macroalgal beds, the relationships between macroalgal metabolism and associated carbon flows are still poorly understood. In the present study, we investigated carbon flows, including air–water CO2 exchange and budgets of dissolved inorganic carbon, total alkalinity, and dissolved organic carbon (DOC) in a temperate macroalgal bed during productive months of the year. To assess the key mechanisms of CO2 sequestration by the macroalgal bed, we estimated macroalgal metabolism and lateral carbon flows using a field-bag method, a degradation experiment, and mass balance modelling over a diurnal cycle. Our results showed that macroalgal metabolism and lateral carbon flows driven by water exchange affected air–water CO2 exchange in the macroalgal bed and the surrounding waters. Macroalgal metabolism caused overlying waters to contain low concentrations of CO2 and high concentrations of DOC that were efficiently exported offshore from the macroalgal bed. The exported water lowered CO2 concentrations in the offsite surface water and enhanced atmospheric CO2 uptake. Our findings suggest that macroalgal beds in habitats associated with high water exchange rates can create extensive CO2-sinks around them.

Kenta Watanabe et al.
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Kenta Watanabe et al.
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Short summary
Macroalgal beds are among the vegetated coastal ecosystems that absorb atmospheric CO2. We investigated the relationships between macroalgal metabolism and inorganic and organic carbon fluxes in a temperate macroalgal bed during the productive time of year. The macroalgal metabolism formed water with low CO2 and high dissolved organic carbon concentrations that was then exported offshore. This export process lowers CO2 concentrations and enhances CO2 absorption in and around macroalgal beds.
Macroalgal beds are among the vegetated coastal ecosystems that absorb atmospheric CO2. We...
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