137Cs in sediments of northern and middle Adriatic sea

The activity of 137Cs in relatively shallow northern and middle Adriatic open sea bottom sediments was obtained on the basis of gamma-spectrometry measurement results of 33 sediment box cores. Cores were sampled during the ASCOP 16 (Adriatic Scientific CO-operative Program) cruise in summer 1990 along seven different transects stretching between the borders of Croatian and Italian territorial waters. 137Cs was determined in the recent sea bottom sediments (0-3 cm) as well as in older, 12-15 cm deep sediment cores. It was found that the lowest caesium concentrations correspond to sands which are spread along the Croatian coast mainly. Parallel to the Italian coast, 137Cs concentrations are the highest in pellets, mud, silt and clay composed bottom. It seems that the influence of Po River is significant for 137Cs activities in recent marine open sea bottom sediments along Italian coast south of Po River delta. Significantly higher 137Cs activities in 0-3 cm vs. 12-15 cm open sea bottom sediment layer can be attributed to the deposition caused by Chernobyl accident. The absence of 137Cs in few middle Adriatic 12-15 cm deep core indicates (in spite bioturbation that caused sediment mixing) significantly lower sedimentation rate in open sea of middle Adriatic vs. northern Adriatic and main deposition area of suspended matter carried by Po River. (author)