Coastal ecosystems release or absorb carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), but the net effects of these ecosystems on the radiative balance remain unknown. We compiled a dataset of observations from 738 sites from studies published between 1975 and 2020 to quantify CO2, CH4 and N2O fluxes in estuaries and coastal vegetation in ten global regions. We show that the CO2-equivalent (CO2e) uptake by coastal vegetation is decreased by 23–27% due to estuarine CO2e outgassing, resulting in a global median net sink of 391 or 444 TgCO2e yr−1 using the 20- or 100-year global warming potentials, respectively. Globally, total coastal CH4 and N2O emissions decrease the coastal CO2 sink by 9–20%. Southeast Asia, North America and Africa are critical regional hotspots of GHG sinks. Understanding these hotspots can guide our efforts to strengthen coastal CO2 uptake while effectively reducing CH4 and N2O emissions.
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All of the data included in this study are freely available at https://doi.org/10.6084/m9.figshare.22351267. These data may be used if cited appropriately.
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We thank the RECCAP2 Scientific Committee and members of the Global Carbon Project who initiated this group effort (https://www.globalcarbonproject.org/reccap/index.htm). We thank the following members of the AmeriFlux site teams who contributed annual net ecosystem CO2 exchange sums for their sites: E. Stuart-Haëntjens, B. Bergamaschi, L. Windham-Myers, A. Vázquez-Lule, R. Vargas, J. Shahan, P. Oikawa, P. Hawman, D. Mishra, R. Sanders-DeMott and P. Polsenaere. J.A.R. and T.M. acknowledge funding from the Hutchinson Postdoctoral Fellowship of the Yale Institute for Biospheric Studies at Yale University. I.F. acknowledges the National Science Foundation Long Term Ecological Research program (OCE 1637630). R.G.N. acknowledges support from the National Aeronautics and Space Administration’s Carbon Cycle Science Program. G.G.L. is a research associate of the F.R.S.–FNRS at the Université Libre de Bruxelles. P.R. received financial support from the Belgian Science Policy Office (through the project ReCAP, which is part of the Belgian research program FedTwin), the European Union’s Horizon 2020 research and innovation program ESM2025—Earth System Models for the Future project (grant number 101003536) and the F.R.S.–FRNS PDR project T.0191.23. B.D.E. acknowledges support from Australian Research Council grants DP220100918, LP200200910 and LP190100271. W.-J.C. acknowledges support from the National Oceanic and Atmospheric Administration and National Science Foundation. J.J.M.B. acknowledges the computational resources provided by Princeton Institute for Computational Science and Engineering, which were used for the land segmentation. B.V.D. was supported by the Bundesministerium für Bildung und Forschung project CARBOSTORE (number 03F0875A), as well as the German Academic Exchange Service project ‘The ocean’s alkalinity: connecting geological and metabolic processes and time-scales’ (number 57429828).
The authors declare no competing interests.
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Extended Data Fig. 1 Regional and global surface areas of estuaries and coastal vegetation.
Surface areas of estuaries a) as a relative percentage (%) and b) in km2 of tidal systems and deltas, lagoons, and fjords in the ten RECCAP2 regions and globally. Surface areas of coastal vegetation c) as a relative percentage (%) and d) in km2 of mangroves, salt marshes, and seagrasses in the ten RECCAP2 regions and globally. The global surface area for estuaries is 733,801 km230. The global coastal vegetation area is 512,982 km2. Surface areas (km2) for each estuary and coastal vegetation type in each of the ten regions can be found in Supplementary Table S4.
Extended Data Fig. 2 Distribution of regional coastal vegetation.
Extended Data Fig. 3 Greenhouse gas study site locations in estuaries and coastal vegetation.
Map showing locations of CO2, CH4, and N2O flux studies in the ten RECCAP2 regions in estuaries (left side): tidal systems and deltas, lagoons, and fjords, and coastal vegetation (right side): mangroves, salt marshes, and seagrasses, from peer-reviewed publications until the end of 2020. The number of study sites can be found in Supplementary Table S8.
Extended Data Fig. 4 Bootstrapping approach.
Bootstrapping was applied to randomly resample flux densities of the three greenhouse gases (level 1) for each estuary or coastal vegetation types (level 2) for each of the ten RECCAP2 regions (level 3) before upscaling to specific surface areas (see Supplementary Table S4).
Supplementary text, PRISMA flow chart and Tables 1–8.
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Rosentreter, J.A., Laruelle, G.G., Bange, H.W. et al. Coastal vegetation and estuaries are collectively a greenhouse gas sink. Nat. Clim. Chang. (2023). https://doi.org/10.1038/s41558-023-01682-9