Distribution of dissolved forms of iron and manganese in the Black Sea

Dissolved forms of the redox-sensitive elements manganese (MnDISS) and iron (Fe(II) and Fe(III)) were measured in the oxic/anoxic transition zone, or suboxic zone, of the Black Sea. An offset was found between dissolved manganese and iron gradients at all stations. In the western cyclonic gyre of the Black Sea, the onset of dissolved Mn (>0.1 μM) was located at a density of about σt=15.85, where the concentration of dissolved oxygen (DO) was less than 5 μM. The onset of dissolved Fe(II) (>0.025 μM) was at σt=15.90, just above the increases in hydrogen sulfide. These characteristic features were modified in the southern coastal waters by such physical processes as the rim current, formation of anticyclonic eddies, and injection of saline, oxygenated Marmara Sea waters from the Bosporus in the Bosporus Plume.