Untersuchungen zum Schwefelkreislauf in Sedimenten am Makran-Akkretionskeil im Arabischen Meer und in Becken der Ostsee
To investigate the cycle of sulfur compounds within the sea bottom of high productivity zones sediments from the Arabian Sea offshore the Makran coast in Pakistan and sediments from the Baltic Sea deep basins were characterised microbiologically and geochemically. Twenty locations in the Arabian Sea were examined, five of them thoroughly. In the Baltic Sea nine locations were sampled up to four times each in the period from 1996 to 1998, with the main emphasis on the Gotland Deep. Depth profiles of reduced sulfur compounds (sulfide, elemental sulfur, thiosulfate, tetrathionate, sulfite) are presented together with profiles of bacterial sulfate reduction rates and thiosulfate oxidation rates, content of organic matter, redox potential, nutrient content, pH value, iron content, and the occurrence of sulfur oxidizing bacteria. The feasibility of BERNER's diffusion model (1964) for the determination of sulfate reduction rates in the investigated area is discussed. Sites at the Makran area within the oxygen minimum zone around cold seeps are populated by sulfur bacterial mats consisting of specimens from the genera Beggiatoa and Thioploca. A model of an idealised sediment is proposed for these locations. Based on depth profile data from the Baltic Sea basins the formational and transformational processes of reduced sulfur compounds, in particular elemental sulfur, are discussed. For the first time evidence was found that sulfite occurs in anoxic and suboxic sediments of the Baltic Sea basins. The appearance of tetrathionate is discussed in connection with the salt water inflow in 1994 into the central Gotland Deep.