The age of consecutive layers was determined using two models: the CF:CS model according to equation (5) (Table 6) and the CRS model based on equation (7) (Figure 6). The relation between layer age and cumulative depth

can be described by a second-degree polynomial (equation Figure 6). The deepest sediment layers, at depths between 14.4 selleck screening library and 15.6 cm, were deposited around 1900. The results obtained using the two models hardly vary at all (Figure 7). The increase in 137Cs isotope activity after 1945 could be attributed to the beginning of atmospheric nuclear tests. However, although no specific peaks appeared corresponding to the increase in test intensity between 1958 and 1963, 137Cs activity did increase Belnacasan continuously towards younger layers in the vertical profile. Moreover, the curve of caesium activity changes in time did not show a clear peak relating to the Chernobyl accident in

1986. As a result of this accident, when large amounts of 137Cs were released into the Baltic Sea (it was estimated that 4.7 TBq of 137Cs were introduced into the sea through precipitation (HELCOM, 1995, HELCOM, 2003, HELCOM, 2009 and Nielsen et al., 1999)), considerable increases in 137Cs concentrations were also recorded in the marine sediments. After 1997, the increase in 137Cs activity stabilised at the level of 190 Bq kg− 1 d.w., which can be linked to changes in the water column. Since 1991, the 137Cs activity in the water column has been declining continuously (Zalewska & Lipska 2006), mainly as a result of radioactive decay and exchange of water with the North Sea; these processes are also reflected by the recently observed lower activities of that isotope in the seabed. A typical distribution of 137Cs concentrations was not identified in the sediment profile; this may be due to the redistribution of radiocaesium within the sediment column. Such GPX6 redistribution could have been due to two main processes: (i) physical

and biological mixing at or near the sedimentwater interface (in the Outer Puck Bay undisturbed sedimentation is not really possible owing to the high dynamics of the water) and (ii) chemical diffusion or advection within the pore water. Sediment mixing typically results in a flattening of the 210Pb activity profile versus depth in the surficial sediment layers, this being the case with the results obtained in the present work (Figure 4). Nevertheless, it can be assumed that the acquired characteristics confirm the correctness of the adopted research methodologies for assessing the rates of sediment accumulation and dating. At the same time, because of the complexity and multitude of processes that may influence final results, the interpretation of activity curves is rarely straightforward and unequivocal. To compare the material collected in the sediment traps with the surface sediment layer from core sampling, activity measurements of 210Pb and 214Bi were conducted in material collected in trap No. 3 (Table 6).