First Finding of Vivianite in Kara Sea Bottom Sediments

Vivianite, an authigenic mineral from the phosphate class, was discovered in Kara Sea bottom sediments for the first time. Similar finds of vivianite were previously known only for the outer shelf of the Laptev Sea, the northern Barents Sea, and the eastern White Sea. Its presence in the subsurface sedimentary strata indicates desalinization of the surface layer of the sea. Core 7444, sampled in a tectonic depression in the Kara Sea during the first stage of cruise 89 of the R/V Akademik Mstislav Keldysh (2022), uncovered Holocene sedimentary strata up to 6.19 m thick. Coarse-silty and sandy vivianite formations are found throughout the entire core, starting from 0.11 m. Vivianite was investigated by a set of methods: optical microscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. The morphology, microstructures, and chemical composition of vivianite formations have been studied. Three morphological types of these formations have been identified: micronodules and their intergrowths, crystalline aggregates and their intergrowths, and tubular aggregates.