These two man-made radionuclides generated from nuclear waste and the detonation of bombs, behave somewhat differently from each other in the marine environment. However, the way they adsorb, that is, the way they attach to the sediment, is strikingly similar. Once attached to the sediment, the radionuclides are essentially removed from the marine environment. To some extent these do control adsorption. First, think of a grain of beach sand.
Clay minerals are products of the rock that makes up most of Siberia and the surrounding mountains.
These minerals provide the source for the mineralogy for the Kara Sea. Their properties can be easily measured and distributions displayed. From there, the properties correlate to another measurable quantity, the radionuclide concentration. Besides sediment, another component inherent in most marine environments is organic matter. Its concentration is partially determined by the sediment properties.