Sulfate reduction in marine sediments from the Baltic Sea-North Sea Transition

Abstract

The spatial distribution and intensity of sulfate reduction was studied in the upper 0-15 cm of coastal sediments by radiotracer technique. The study area extended from the eastern North Sea through Skagerrak and Kattegat into the Belt Sea at the entrance to the Baltic Sea. The 27 sampling stations ranged from pure sand to clayey mud with organic contents from 0.2 to 13% dry weight. Water depths ranged from 7 to 200 m. Depth-integrated sulfate reduction rates were mostly 1-5 mmol m^-2 d^-1 in the Skagerrak-Kattegat-Belt Sea area. Lowest rates, 0.08-1.0 mmol m^-2 d^-1, were encountered in low-organic sands from exposed parts of the North Sea. Extremely high rates, 17-30 mmol m^-2 d^-1, were found in the Helgoland Bight, SE North Sea, near the mouth of the Elbe River. Intensive sulfate reduction was associated with areas offine-grained sediment and with high deposition rates of organic detritus, The degree of pyritization correlated positively to sulfate reduction rates (r = 0.63) and to FeS concentrations (r = 0.70). In deeper stations of northern Kattegat and Skagerrak, < 5% of the iron occurred as pyrite.