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.