Vertical distribution of thiosulfate and sulfite in the Black Sea

We obtained the data on the vertical distribution of thiosulfate and sulfite by derivatization with monobromobimane in the water column of the Black Sea for the first time. Thiosulfate and sulfite appeared in detectable quantities below the redox interface along with the appearance of hydrogen sulfide. On the continental slope, the concentration of sulfite reaches 1.12 µM, and thiosulfate 0.53 µM in sea water with a potential density of 16.40–16.80 kg/m3. In the deep part of the sea at a depth of 400 m (potential density 16.96 kg/m3), the concentrations of sulfite and thiosulfate reach their maximum of 1.74 µM and 0.98 µM, respectively. A comparison of data on thiosulfate obtained after filtration and without filtration showed that in the upper part of the anoxic layer, up to 100% of thiosulfate is associated with bacterioplankton. Microbial bound thiosulfate in the cell gradually decreases to a depth of 600 m. These data and the correlation with sulfite and particulate organic carbon suggest that in the upper part of the anoxic zone, thiosulfate and sulfite are predominantly a result of the activity of chemoautotrophic bacteria.