Reduced sulfur in the hypersaline anoxic basins of the Mediterranean Sea

The hypersaline anoxic basins of the eastern Mediterranean Sea were studied for their reduced sulfur chemistry. In the deep waters, hydrogen sulfide reaches 3 mM in the Bannock Basin brine and 2.2 mM in the Tyro Basin brine. These are among the most sulfidic bodies of water known in the marine environment. No intermediate oxidation state compounds of sulfur were detected. The seawater/Bannock Basin brine interface is a zone < 3.95 (± 1.25) m. This is one of the steepest pycnocline gradients known. The zone of intense sulfide oxidation occurs < 2.8 m below the interface. Based on δ 34S measurements of dissolved sulfate, sulfate reduction occurs at the seawater/brine interface. Trace amounts of H 2S are released from the interface and the H 2S mixes with waters from the sea. This released H 2S affects the speciation of other redox-sensitive elements above the seawater/brine interface. An intercalibration of the polarographic method with the Cline method for sulfide determinations performed in 1987 shows very good agreement. The Hg(II) titration method for the determination of sulfide was used in 1988 and shows no difference in sulfide concentration over the 1-year period between samplings.