A Thiosulfate Shunt in the Sulfur Cycle of Marine Sediments

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Abstract
The oxidation of sulfide, generated by bacterial sulfate reduction, is a key process in the biogeochemistry of marine sediments, yet the pathways and oxidants are poorly known. By the use of 35 S-tracer studies of the S cycle in marine and freshwater sediments, a novel shunt function of thiosulfate (S 2 O 3 2- ) was identified. The S 2 O 3 2- constituted 68 to 78 percent of the immediate HS - -oxidation products and was concurrently (i) reduced back to HS - , (ii) oxidized to SO 4 2- , and (iii) disproportionated to HS - + SO 4 2- . The small thiosulfate pool is thus involved in a dynamic HS - - S 2 O 3 2- cycle in anoxic sediments. The disproportionation of thiosulfate may help account for the large difference in isotopic composition ( 34 S/ 32 S) of sulfate and sulfides in sediments and sedimentary rocks.