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An isotope view on calcium gradients in the Baltic Sea

The modern Baltic Sea (BS) surface water is characterized by an excess in dissolved calcium (Ca) of still unknown origin. Our hydrogeochemical study uses the stable isotopes of Ca and carbon to identify potential calcium sources. The composition of dissolved Ca was analyzed in bottom waters of the deep BS basins, in potential freshwater sources, like rivers and creeks draining the southern coastline, as well as submarine groundwater discharge. The role of sediments was followed in a porewater gradient from the Gotland deep basin in the central BS. The results are traced compared to the North Sea and selected tributaries.

Values of Ca isotope in the bottom waters of the BS deeps shift towards more negative values with decreasing salinity and increasing Ca excess. In the porewater, a downward increase in Ca concentrations and decrease in Ca isotope values is associated with weathering of carbonates and/or Ca desorption from clays. The isotope composition of dissolved Ca in the Warnow river draining into the southern BS was within the range of other European rivers, lower than seawater, but more positive than that of rivers draining into the North Sea. Weathering of carbonates by groundwater was found to be a further Ca source depleted in 44Ca. Seasonal variations in the Warnow River, with most positive values during summer, are likely due to internal processes that cause Ca carbonate formation in the water column. Concluding, dissolved Ca in the fresh part of salinity gradients originates from carbonate weathering.

Support: DFG, BMBF, DAAD, IOW

Details

Author
Michael Ernst* Böttcher1, Cátia Milene Ehlert von Ahn2, Anna-Kathrina Jenner3, Patricia Roeser4, Sylvia Riechelmann5, Adrian Immenhauser5, Nikolaus Gussone6, Olaf Dellwig3, Laura Lapham7, Vera Winde8
Institutionen
1Geochemistry & Isotope Biogeochemistry, Leibniz IOW, Germany;Geography & Geology, Greifswald University, FRG;Interdisciplinary Faculty, Rostock University, FRG; 2Geochemistry & Isotope Biogeochemistry, Leibniz IOW, Germany;Leibniz ZMT, Bremen, FRG; 3Geochemistry & Isotope Biogeochemistry, Leibniz IOW, Germany; 4Geochemistry & Isotope Biogeochemistry, Leibniz IOW, Germany;Environmental Geology, Institute for Geosciences, University of Bonn, FRG; 5Institute of Geology, Mineralogy and Geophysics, Ruhr-University Bochum, Bochum, FRG; 6Institute of Mineralogy, University of Münster, FRG; 7Chesapeake Biological Laboratory, University of Maryland, Center for Environmental Science, USA; 8Geochemistry & Isotope Biogeochemistry, Leibniz IOW, Germany;present address: Hydroisotop, Schweitenkirchen, FRG
Veranstaltung
Geo4Göttingen 2025
Datum
2025
DOI
10.48380/6akb-bj28

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