THE OXIDATION OF H2S IN BLACK-SEA WATERS

The oxidation of H2S with oxygen was measured in Black Sea Waters at 25-degrees-C. The measurements were made on mixtures of deep waters and surface waters. The oxidation rates were found to be 10 times faster than the rates for surface seawater (Black Sea and Gulf Stream) with added H2S. Since the rates were the same for filtered (0.2-mu-m) and unfiltered waters, the increase in the rates appears to be abiotic and caused by solutes dissolved in the deep waters. Laboratory measurements indicate that dissolved Fe2+ is the likely cause of the rate increase. The oxidation of Fe(II) yields particulate Fe(III) that can catalyse the oxidation and also oxidize H2S. Preliminary measurements of the rates of oxidation of SO32- and S2O32- in oxygenated deep Black Sea waters are also presented. These measurements indicate that particulate Fe(III) also may accelerate the rates of oxidation of SO32-.