Radium isotopes as submarine groundwater discharge (SGD) tracers: Review and recommendations

J. Garcia-Orellana, V. Rodellas, J. Tamborski, M. Diego-Feliu, P. van Beek, Y. Weinstein, M. Charette, A. Alorda-Kleinglass, H. A. Michael, T. Stieglitz, J. Scholten

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Submarine groundwater discharge (SGD) is now recognized as an important process of the hydrological cycle worldwide and plays a major role as a conveyor of dissolved compounds to the ocean. Naturally occurring radium isotopes (223Ra, 224Ra, 226Ra and 228Ra) are widely employed geochemical tracers in marine environments. Whilst Ra isotopes were initially predominantly applied to study open ocean processes and fluxes across the continental margins, their most common application in the marine environment has undoubtedly become the identification and quantification of SGD. This review focuses on the application of Ra isotopes as tracers of SGD and associated inputs of water and solutes to the coastal ocean. In addition, we review i) the processes controlling Ra enrichment and depletion in coastal groundwater and seawater; ii) the systematics applied to estimate SGD using Ra isotopes and iii) we summarize additional applications of Ra isotopes in groundwater and marine studies. We also provide some considerations that will help refine SGD estimates and identify the critical knowledge gaps and research needs related to the current use of Ra isotopes as SGD tracers.

Original languageEnglish
Article number103681
JournalEarth-Science Reviews
StatePublished - Sep 2021

Bibliographical note

Publisher Copyright:
© 2021 The Authors


The authors would like to thank T. Horscroft for the invitation to write this review and W.S. Moore, S. Lamontagne and three anonymous reviewers for their constructive comments on the manuscript. J.Garcia-Orellana acknowledges the financial support of the Spanish Ministry of Science, Innovation and Universities , through the “Maria de Maeztu” programme for Units of Excellence ( CEX2019-000940-M ), the Generalitat de Catalunya (MERS; 2017 SGR – 1588) and the project OPAL (PID2019-110311RB-C21). V. Rodellas acknowledges financial support from the Beatriu de Pinós postdoctoral program of the Generalitat de Catalunya ( 2017-BP-00334 and 2019-BP-00241 ). M. Charette received support from the U.S. National Science Foundation ( OCE-1736277 ). J. Scholten acknowledges the support through the SEAMOUNT BONUS project (art. 185), which is funded jointly by the EU and the Federal Ministry of Education and Research of Germany (BMBF, grant no. 03F0771B ). P. van Beek and T. Stieglitz acknowledge support from the French ANR project MED-SGD (ANR-15-01CE-0004) and chair @RAction MED-LOC ( ANR-14-ACHN-0007-01 ). A. Alorda-Kleinglass acknowledges financial support from ICTA “Unit of Excellence” (MinECo, MDM2015-0552-17-1 ) and PhD fellowship, BES-2017-080740. H. Michael acknowledges support from the U.S. National Science Foundation ( EAR-1759879 ). M. Diego-Feliu acknowledges the financial support from the FI-2017 fellowships of the Generalitat de Catalunya ( 2017-FIB-00365 ). Figs. 3, 4, 7 and 12 were designed by Gemma Solà ( www.gemmasola.com ).

FundersFunder number
Beatriu de Pinós
ICTA2017-FIB-00365, EAR-1759879, BES-2017-080740, MDM2015-0552-17-1
MERSPID2019-110311RB-C21, 2019-BP-00241, 2017 SGR – 1588, 2017-BP-00334
National Science FoundationOCE-1736277
Ministerio de Ciencia, Innovación y UniversidadesCEX2019-000940-M
European Commission
Bundesministerium für Bildung und ForschungANR-14-ACHN-0007-01, 03F0771B, ANR-15-01CE-0004
Generalitat de Catalunya


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