Sediment transport pathways in the Skagerrak and Kattegat as indicated by sediment Chernobyl radioactivity and heavy metal concentrations

The concentration of the heavy metals Hg, Cu, Pb and Zn as well as Chernobyl Cs-137 radioactivity was determined in surface sediments from the Skagerrak and Kattegat. Sediment samples from adjacent Swedish fjords were analysed as well. The sampling was carried out between spring 1988 and autumn 1990. Highest concentrations of heavy metals and largest Cs-137 activities occur in fine-grained organic-rich (> 62; 2% C org) sediment from Swedish inshore waters and locally also in the Kattegat. Regional trends of relative enrichment of the various heavy metals and Chernobyl Cs-137 with respect to organic carbon was used to determine transport patterns of material enriched with respective elements. It can be proven that deposition of fine-grained material transported from the (southern) North Sea by the Jutland Current is the main mechanism determining the regional accumulation of lead and Chernobyl-derived Cs-137. This mechanism principally controlls the areal distribution of mercury-enriched material as well, but it is regionally of less importance as far as the accumulation of Cu and Zn concerns. The Chernobyl Cs-137 data show that a large proportion of the fine-grained material transported by the Jutland Current originally is river-borne suspension load from (central) western Europe. The areal enrichment pattern of copper, and on a smaller scale those of mercury and zinc too, points to westerly directed suspension load transport across the Kattegat. Material enriched with these elements apparently is being discharged from Swedish industrial and urban centers, in particular the Göteborg area.