The presence of the elements Ni, Co, Cu, Mo, and V was determined in deep-water sediments. The irregular distribution of elements in Black Sea deposits is explained by the geochemical evolution of the basin in postglacial times and is controlled by several factors. Chief among these factors are the change in hydrodynamic regime and the decreasing rate of sedimentation in post-Neoeuxinian time. Subsidiary factors, beginning during Old Black Sea time, include the increasing proportion of organic matter in the sediments; the appearance and stabilization of H₂S in bottom water; and the initiation of the Bosporus underflow, which brought Mediterranean water into the Black Sea.

Maximum concentrations of Mo, V, Co, Ni, and Cu are found in the sapropelic muds of the Old Black Sea deposits. Special studies of sapropels have established clear correlations between Cu, Ni, Mo, and V concentrations and organic matter. This relation does not hold true for cobalt; cobalt concentrations correlate with sulfide (represented basically by pyrite). Examination of bitumen, humic acid, and fulvic acid fractions shows that some part of the metals is present in the organic matter itself. Higher concentrations of microelements in the sapropels result from absorption of metals from seawater by organic detritus during settling of the particulates. Accumulations of metals by living planktonic organisms is subordinate.

Mo, Co, Ni, and Cu also were analyzed in pyrite from deep-water sediments of the H₂S zone of the Black Sea. These metals were significantly enriched. Mean concentrations and enrichment factors (in comparison with host sediments) are: MoO₃, 0.1 percent (36); CoO, 0.017 percent (9); NiO, 0.15 percent (18); and CuO, 0.13 percent (20).

We conclude that sulfides are a significant factor in the geochemical balance of these metals in Black Sea sediments.