EGU General Assembly 2021
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Global trends in air-water CO2 exchange over seagrass meadows revealed by atmospheric Eddy Covariance

Bryce Van Dam1, Pierre Polsenaere2, Aylin Barreras-Apodaca3, Christian Lopes4, Zulia Sanchez-Mejia3, Tatsuki Tokoro5,6, Tomohiro Kuwae6, Lucia Gutiérrez Loza7, Anna Rutgersson7, James Fourqurean4, and Helmuth Thomas1
Bryce Van Dam et al.
  • 1Helmholtz-Zentrum Geesthacht, Institute of Coastal Research, Geesthacht, Germany (
  • 2Ifremer, Laboratoire Environnement et Ressources des Pertuis Charentais (LER-PC), BP133, 17390, La Tremblade, France
  • 3Instituto Tecnológico de Sonora, Ciudad Obregón, Sonora, México
  • 4Department of Biological Sciences and Center for Coastal Oceans Research, Florida International University, Miami, Florida, USA
  • 5Coastal and Estuarine Environment Research Group, Port and Airport Research Institute, Yokosuka, Japan
  • 6National Institute for Environmental Studies, Center for Global Environmental Research (CGER), Office for Atmospheric and Oceanic Monitoring, Onogawa, Tsukuba, Ibaraki, Japan
  • 7Department of Earth Sciences, Uppsala University, Uppsala, Sweden

Coastal vegetated habitats like seagrass meadows can mitigate anthropogenic carbon emissions by sequestering CO2 as “blue carbon” (BC). Already, some coastal ecosystems are actively managed to enhance BC storage, with associated BC stocks included in national greenhouse gas inventories. However, the extent to which BC burial fluxes are enhanced or counteracted by other carbon fluxes, especially air-water CO2 flux (FCO2) remains poorly understood. To this end, we synthesized all available direct FCO2 measurements over seagrass meadows made using a common method (atmospheric Eddy Covariance), across a globally-representative range of ecotypes. Of the four sites with seasonal data coverage, two were net CO2 sources, with average FCO2 equivalent to 44 - 115% of the global average BC burial rate. At the remaining sites, net CO2 uptake was 101 - 888% of average BC burial. A wavelet coherence analysis demonstrates that FCO2 was most strongly related to physical factors like temperature, wind, and tides. In particular, tidal forcing appears to shape global-scale patterns in FCO2, likely due to a complex suite of drivers including: lateral carbon exchange, bottom-driven turbulence, and pore-water pumping. Lastly, sea-surface drag coefficients were always greater than prediction for the open ocean, supporting a universal enhancement of gas-transfer in shallow coastal waters. Our study points to the need for a more comprehensive approach to BC assessments, considering not only organic carbon storage, but also air-water COexchange, and its complex biogeochemical and physical drivers.

How to cite: Van Dam, B., Polsenaere, P., Barreras-Apodaca, A., Lopes, C., Sanchez-Mejia, Z., Tokoro, T., Kuwae, T., Gutiérrez Loza, L., Rutgersson, A., Fourqurean, J., and Thomas, H.: Global trends in air-water CO2 exchange over seagrass meadows revealed by atmospheric Eddy Covariance, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2283,, 2021.

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