Sedmentation in the Central Baltic Sea as Viewed by Non-Destructive Pb-210-dating

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Abstract
Geografisk Tidsskrift, Danish Journal of Geography 98:1–9. A non-destructive gamma-spectrometric method was used to assay the sedimentation in the central Baltic Sea. Three cores from the Gotland Deep with water depths exceeding 230 m showed relatively high Pb-210 and Cs-137 but relatively little variation between cores in the curves for unsupported Pb-210. A constant rate of supply (CRS) modelling of the data revealed that there is a tendency of increasing linear sedimentation rates, from 0.5 to 2 mm a−1, since 1950. With the measured bulk density profiles this is accompanied by increasing sediment accumulation rates (from about 200 to 600 g m−2 a−1) There are generally moderately increased Cs-137 values found in the deep and these may mainly be ascribed to the Chernobyl accident. A core from the central Gdansk Basin taken at a water depth of 117 m shows relatively lower Pb-210 values and a more structured unsupported Pb-210 distribution with depth. A very high activity (about 4000 Bq kg−1) sediment slice (8–9 cm depth) can according to the CRS modelling be ascribed to year 1986. The high activity, however, was found to be confined to a small part of the sediment slice material and therefore this has some bearing on the depositional mechanism of Cs-137 in the sediments.

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