Distribution features of ²³⁸U, ²³²Th and ²²⁶Ra in bottom sediments of the shelf and continental slope of Svalbard

The features of the distribution of concentrations of ²³⁸U, ²³²Th and ²²⁶Ra in the surface layer of bottom sediments in the bottom sediments of the shelf and continental slope of Svalbard are considered. The content of ²²⁶Ra,²³²Th, and ²³⁸U varied in the range 22–134.3, 22.4–50.9, and 10.9–37.7 Bq/kg, respectively. The amount of ²²⁶Ra nonequilibrium with ²³⁸U (²²⁶Ra_ex) ranged from 23 to 73% of the total ²²⁶Ra content in sediments. The maximum concentrations of ²²⁶Ra, ²³⁸U,²³²Th and ²²⁶Ra_ex (134.3, 37.7, 50.9, and 98.2 Bq/kg, respectively) were obtained in the area of increased bioproductivity (Eagle Trough). In this zone, the relationship between the concentrations of ²²⁶Ra and ²²⁶Ra_ex with the content of organic matter in sediment is well expressed, the correlation coefficients are R = 0.94 and 0.92, respectively, which indicates a significant contribution of the biological community to the accumulation of ²²⁶Ra in bottom sediments. The ²²⁶Ra concentration and the ²²⁶Ra excess value are negatively related to the redox potential of the sediment (R = –0.88). This pattern is also true in other areas of the Svalbard waters. In general, for the entire array of observations, the concentrations of ²³⁸U and ²³²Th increase with increasing content of organic carbon in the sediment (R = 0.72 and 0.7, respectively). The concentrations of ²³⁸U and ²³²Th decrease with increasing C_carb content in the sediment (R = –0.79 and –0.81, respectively). The data obtained indicate the need to take into account the ²²⁶Ra excess when assessing the total natural radioactivity of marine sediments, the value of which may exceed the radioactivity of ²³⁸U and ²³²Th.