Recent sediment accumulation in Skagerrak as depicted by 210pb-dating

Trends of modem rates of sediment accumulation have been studie in four cores from the Skagerrak, one of which was also analysed for anthropogenic zinc fluxes. The cores were collected from the Norwegian Channel off Kristiansand at 522 m, off Hirtshals at 239 m and 454 m, and from the NE slope
off Larvik at 230 m water depth. Accumulation rates of the last 100 to 150 years were determined by 210pb dating, partially supported by 137Cs analysis.
Average sedimentation rates were 2.5, 2.1, and 1.6 mm/year or 0.14, 0.10, and 0.15 g/cm2 year for the cores from 522, 454 and 239 m water depth, respectively. Sediment accumulation might have varied systematically during the last 150 years. One pronounced break occurred some 100 to 140 years ago.
An extremely rapid sediment growth of 11 mm/year or 0.75 g/cm2 year was found for the NE Skagerrak core. The first significant appearance of man-released zinc in this core was dated at about A.D. 1860. The
total Zn flux to the sediments has tripled since then, with the modem impact amounting to 260 mg Zn/cm2 year from anthropogenic sources.
Acid extractable supported 210Pb was found to be fractioned among the ela y, silt and sand size classes
of the sedimentary particulates as 65:24:11. For the silt plus clay fraction, excess 210Pb specific activities of the surface sediments appeared to be largely independent of dry matter accumulation rates (thus favouring the constant concentration model of 210pb dating), and excess 210Pb is supplied to the sediments at rates greatly in excess of atmospheric fall-out. Both these results are considered to reflect export of fine-grained particles from higher energetic shallow water environments in the North Sea and/or Baltic and sediment transport to the depositories at greater water depth on a time scale comparable with the half-life of 210pb.