Abstract
The coastal ocean links land and sea through rivers and submarine groundwater discharge, which contribute to the coastal carbon budget. Groundwater discharge, including fresh groundwater and recirculated seawater, remains poorly constrained globally. Here, we compile a global dataset of coastal groundwater chemistry and estimate fluxes of dissolved inorganic carbon and total alkalinity. Using conceptual reaction models, we analyze the alkalinity-carbon relationship to identify dominant processes. These patterns reflect carbonate dissolution and precipitation, and organic matter remineralization under oxic and anoxic conditions, indicating that coastal aquifers function as geochemical reactors. Recirculated seawater sampled inland is more enriched than nearshore groundwater, consistent with longer residence time and enhanced water-rock interaction. Groundwater contributes 3–7 percent of riverine dissolved inorganic carbon flux, equivalent to 2.7–2.9 and 2.2-2.4 trillion moles per year of dissolved inorganic carbon and alkalinity, depending on lithology and redox conditions. This emphasizes the importance of incorporating groundwater fluxes into Earth system models.
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Data availability
The study uses compiled groundwater geochemical data (dissolved inorganic carbon (DIC), total alkalinity (TA), pH, major ions concentration, salinity classification, lithology, and derived mixing) from 58 previously published studies. The processed and harmonized dataset used for the global submarine groundwater discharge (SGD) flux calculations has been deposited in the Zenodo repository and is publicly available at https://doi.org/10.5281/zenodo.18833297.
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Acknowledgements
We want to thank the Sustainability and Energy Research Initiative (SAERI) grant, the Helen Kimmel Center for Planetary Science grant, the Minerva Foundation, the Angel Faivovich Foundation for ecological research, and the De Botton Center for Marine Sciences grant for their funding support for this study. Additionally, we acknowledge the support from the Zuckerman Faculty Scholars program, the Center for Scientific Excellence research grant, the Raymond Lapon Fund research grant, the Estate of David Levinson, the Paul and Tina Gardner research grant, and the Center for New Scientists at the Weizmann Institute of Science research grant.
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Nurit Weber designed the research, compiled and analysed the global groundwater dataset, performed the geochemical and flux calculations, and wrote the manuscript. Yael Kiro contributed to the conceptual framework and research design, interpreted the results, contributed to the development of the reaction-based modeling approach, and revised and edited the manuscript.
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Communications Earth and Environment thanks Gwénaëlle Chaillou and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Nicola Colombo. A peer review file is available.
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Weber, N., Kiro, Y. Alkalinity and carbon fluxes from coastal aquifers to the ocean via submarine groundwater discharge. Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03430-1
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DOI: https://doi.org/10.1038/s43247-026-03430-1
