Specific Features of the 226Ra, 238U, and 232Th Distribution in the Surface Layer of Marine Sediments under the Conditions of Active Biosedimentation in the Arctic Front Zone

Abstract

The distribution of natural radionuclides and organic matter in bottom sediments of the active biosedimentation zone on the section drawn through the arctic front of the North Atlantic was studied. The ratios of the amounts of ²²⁶Ra, ²³⁸U, and ²³²Th, both deposited in the surface layer of bottom sediments from seawater and supplied with the terrigenic material, were estimated. Direct deposition of radium from water to marine sediments correlates with the organic matter content. The concentration of radium that is not in equilibrium with uranium varies in the range 95–99% of the total content and increases with an increase in the content of chloroform-soluble bitominoid (CB) (R = 0.95). The deposition of nonequilibrium ²³⁸U from water to bottom deposits is also significant and ranges from 42 to 69% of the total ²³⁸U content. The concentration ratio of nonequilibrium uranium and nonequilibrium radium in the sediments decreases with increasing depth and increases with an increase in the CB content of the deposit. Positive correlation is observed between the content of thorium and total uranium (R = 0.93) and of its nonequilibrium and terrigenic fractions (R = 0.93 and 0.94, respectively).