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Published (Version of record)CC BY V4.0, Open Access
Published (Version of record)CC BY V4.0, Open
Journal article
Radium isotopes trace cross-shelf nutrient transport in a marginal sea
Estuarine, coastal and shelf science, Vol.325, pp.1-12
10/2025
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Abstract
Nearshore coastal zones play a critical role modulating terrestrial nutrient transport into the ocean. While nutrient dynamics of marginal seas like the Baltic Sea are well documented, they are predominantly based on riverine inputs, overlooking the biogeochemical transformation and exchange of nutrients beyond the estuarine filter. Here, we use short-lived radium isotopes to investigate cross shelf nutrient transport along 14 transects, spatially distributed across 12 locations along the Baltic Sea coastline. The radium tracer approach revealed a horizontal eddy diffusivity rate of (3.9 ± 1.1) x 106 m2 day-1 and nearshore water residence time of 7.6 ± 4.5 days. Cross-shelf nutrient loads extrapolated along the 8000 km coastline were 8.2 ± 2.9 kt Si day-1 for silicate, 0.9 ± 0.5 kt N day-1 for dissolved inorganic nitrogen (DIN), and 0.1 ± 0.02 kt P day-1 for phosphate. DIN loads were 4.5 times higher than average historical river-derived loads for September. Phosphate inputs were 20% higher, while silicate transport rates were 57% lower than the corresponding historical river loads. While comparisons between our radium-derived cross-shelf fluxes with river loads create perspective, they should be seen with care due to potential spatial and temporal biases. Overall, these findings illustrate the use of radium as a tracer of terrestrial inputs and underscore the need to integrate shelf-scale processes beyond the estuarine filter into coastal nutrient assessments.
•Eddy diffusion in nearshore waters drives lateral dispersal of terrestrial nutrient inputs.•Inner-shelf biogeochemical transformations alter nutrient stoichiometry causing phosphorus limitation and silicate enrichment.•Radium derived nutrient loads exceed riverine phosphate and inorganic nitrogen inputs suggesting contributions from lateral subsurface pathways.
Details
- Title
- Radium isotopes trace cross-shelf nutrient transport in a marginal sea
- Creators
- Aprajita S. Tomer - University of GothenburgTristan McKenzie - Department of Earth SciencesClaudia Majtényi-Hill - University of GothenburgTibaud Cardis - University of GothenburgLinnea Henriksson - University of GothenburgPer O.J. Hall - University of GothenburgBeata Szymczycha - Instytut Oceanologii Polskiej Akademii NaukNico Mitschke - Carl von Ossietzky Universität OldenburgIsaac R. Santos - University of Gothenburg
- Publication Details
- Estuarine, coastal and shelf science, Vol.325, pp.1-12
- Publisher
- Elsevier Ltd
- Grant note
- This work was supported by Knut and Alice Wallenberg Foundation, Sweden (grant no: 2022-0096), Swedish Research council (grant nos. 2019-03930 and 2020-00457), and Formas (grant no. 2023-01324).
- Identifiers
- 991013307012102368
- Copyright
- © 2025 The Authors.
- Academic Unit
- Faculty of Science and Engineering; National Marine Science Centre
- Language
- English
- Resource Type
- Journal article