DETERMINATION OF RECENT SEDIMENTATION IN THE GULF OF FINLAND USING CS-137

Linear accumulation rates and dry-matter accumulation rates were deter mined using Cs-137 distribution in sediment cores from 98 coastal and open-sea stations from around the Gulf of Finland (the Baltic Sea). Re sults showed that the average linear accumulation rate varied between 0.05-1.94 (mean 0.60) cm a(-1) which corresponds to a dry-matter accum ulation rate of 0.01-0.30 (mean 0.15) g cm(-2) a(-1). Accumulation rat es were high in recent mud sediments, especially near river outlets. T he highest rates were found at inshore stations near Kotka town. Peak Cs-137 activities in cores from the whole study area varied between 0. 04-2.4 Bq g(-1) wet weight. The highest activities were found in areas most affected by fallout from the 1986 Chernobyl accident, and corres ponded to the overall areal distribution of Cs-137 in the soil but the areal distribution of Cs-137 in the sediments was also caused by the discharge of sedimenting particulate material from land. Total Chernob yl fallout in the area was between 1.4-80.5 (mean 21) kBq m(-2). Mixin g of sediment strata was considerable in the uppermost sediment layers of many soft sediments, as indicated by the width of the Cs-137 peak in the cores. The Cs-137 technique can be used successfully in the Gul f of Finland because of high radiocaesium activities and the high accu mulation rates. With the data obtained, the suitability of the station s for chronological sampling and monitoring was evaluated, and several new sediment stations that could be used for monitoring were identifi ed.