Identification of sulfur species in coastal marine sediments collected from the Seto Inland Sea, Japan in summer

This study investigated the spatial distribution of hydrogen sulfide in sediment pore water and sulfur species in marine sediments of the Seto Inland Sea, the largest enclosed sea in Japan, using a combination of hydrogen sulfide detection tubes and X-ray absorption fine structure spectroscopy to identify sulfur species. The percentage composition of sulfur species in the surface sediments (0-5 cm layer) of the Seto Inland Sea was identified as sulfate (23.1-85.5%), thiosulfate (<5-30.7%), elemental sulfur (<5-31.0%), and pyrite (<5-44.3%). Organic sulfur was identified at some sampling stations. The redox potential of the sediments was positively correlated with the percentage composition of the sum of sulfate and thiosulfate to total sulfur, and was negatively correlated with the percentage composition of the sum of elemental sulfur and pyrite to total sulfur. The percentage composition of sulfate was negatively correlated well with total organic carbon concentration in the sediments. The slope of the linear regression between the percent composition of sulfate and total organic carbon concentration in sediments for the high-load area was approximately two times higher than that of the low- and moderate-load areas. X-ray absorption near the edge structure of iron in the sediments showed that pyrite was oxidized to sulfate coupled with the reduction of iron. In conclusion, the redox potential and total organic carbon concentration in sediments could be simple parameters for estimating sulfur species in sediments from the Seto Inland Sea.