Geochemistry of sediments in the modern Aral Basin

The study presents the first geochemical data on the bottom sediments from the modern desiccating Aral Sea, which allowed a direct comparison between the compositions of the sediments collected during the pre- and postdesiccation periods. This study revealed the differences and similarities in the major and trace element composition of the sediments collected from the former bottom of the Large Aral Sea, the present-day sea bottom, the desiccated sea bottom, and the Amu Darya suspended sediments with respect to the average shale composition. The euxinic sediments from the western deep-water depression are characterized by high concentrations of U, Mo, and organic matter. The precipitation of evaporite salts occurs at the shallowest depths and in the western depression. The salt deposits exposed by the shrinking sea tend to be desalinated due to intense weathering. The mercury detected at high levels in the river suspended sediments of the former Amu Darya discharge was found to be absent in the modern marine sediments due to reductions in the river flow and the possible migration to the atmosphere. Many other trace elements, besides uranium, may also accumulate in seawater.