Strontium in rivers of the Baltic Basin

Abstract

The rivers in the Baltic Basin drain a mixture of bedrocks ranging from Mesozoic-Paleozoic sediments in the south to Proterozoic-Archean intrusives in the north. The rivers in the sedimentary basin in the south have high concentrations of Sr, in the interval 100–500 µg l−1 while the87Sr/86Sr ratio is close to that of seawater, i.e. 0.71. The northern rivers in the Precambrian shield area on the other hand have low Sr concentrations of 15–50 µg l−1 with high87Sr/86Sr ratios of about to 0.73 (0.721–0.745). The riverine input of dissolved Sr to the brackish Baltic Sea approaches 60 tons year−1, with a weighted mean concentration approaching 130 µg l−1 and a weighted mean87Sr/86Sr ratio close to 0.712. Although the sedimentary area in the south supplies only about 43% of the total river discharge, it gives about 88% of the total Sr input. Because of this and the strong regional riverine variation in87Sr/86Sr ratio, Sr and its isotopes seem to be a convenient tool to unveil mixing relations of water masses in the northern Baltic Sea, provided high resolution analyses are applied. For an overall characterization of water mixing in the Baltic Sea, the Nd system will be superior to that of Sr.