Distribution of 137Cs and 40K in the Bottom Sediments of the Balaklava Bay (the Black Sea)

Purpose. The aim of the work is to study spatial variability of the 137Cs and 40K concentrations in the bottom sediments of the Balaklava Bay, and to estimate the sedimentation rate and relative content of the biogenic fraction. Methods and Results. The results of the 137Cs and 40K concentration measurements in 5 columns of the bottom sediments sampled in various parts of the Balaklava Bay are represented. Activity of 137Cs and 40K in the samples was determined by the gamma spectrometric analysis. Based on the measurement data, spatial variability of the 137Cs and 40K concentration fields in the bottom sediments was studied, and the sedimentation rate was quantitatively estimated. Application of the balance equation provided quantitative estimates of the relative biogenic fraction content; its spatial variability was described. Quantitative estimates of the relationship between the biogenic fraction estimates resulted from use of the direct and indirect methods are represented. Conclusions. According to the obtained results, the 137Cs and 40K concentrations in the upper 5 cm layer of bottom sediments varied in space from 11 to 62 and from 155 to 562 Bq/kg, respectively. The maximum radionuclide concentrations were characteristic of the northern part of the bay, the minimum ones – of its southern part. The sedimentation average rate was 0.51 ± 0.06 cm/year. Relative biogenic fraction content in the sediments varied in space from 30 to 89% and averaged 46 ± 25%. The maximum values were observed in the southern part of the bay, the minimum ones – in the northern part.