Recent sedimentation rates across the Norwegian Trough

Abstract

From the systematic sampling of 20 stations of the Norwegian part of the Skagerrak in 1993, six cores were chosen for determination of recent sedimentation rates by the lead-210 method and verifications by Cs-137 depth distributions. By using the gamma-spectrometric variant of the method, both natural and anthropogenic radioisotopes are simultaneously measured in the samples. The highest average linear sedimentation rate (4.7 mm\/year) was found for a core (NC-84) from station 67, on the southern lowermost slope of the Norwegian Trough; a relatively high average sedimentation rate (2.3 mm\/year) was also deduced from the measured data for the core (NC-13) from station 56, taken in its central (deepest) part. The core from the northwestern part of the trough, from stations 69 (NC-97) and 74 (NC-134), showed rates that were close to or somewhat higher than 1 mm\/year, while cores from stations 65B (NC-71) and 71 (NC-113) showed significantly disturbed depth profiles. Usind unsupported lead-210 intensities and the physical data on the cores (water content, dru weight and bulk density of the core slices) it was possible to reconstruct the sedimentation history of the cores. When the modelling (constant rate of supply) is applied to the Cs data, it is obvious that Cs-137 distributions with depth can most likely be explained by three superimposed anthropogenic events: Chernobyl accident, Sellafield release and nuclear bomb testing, with the Sellafield release being the most dominating feature observed in the investigated cores.