The Biogeochemical Sulfur Cycle of Marine Sediments

Abstract

Microbial dissimilatory sulfate reduction to sulfide is a predominant terminal pathway of organic matter mineralization in the anoxic seabed. Chemical or microbial oxidation of the produced sulfide establishes a complex network of pathways in the sulfur cycle, leading to intermediate sulfur species and partly back to sulfate. The intermediates include elemental sulfur, polysulfides, thiosulfate, and sulfite, which are all substrates for further microbial oxidation, reduction or disproportionation. New microbiological discoveries, such as long-distance electron transfer through sulfide oxidizing cable bacteria, add to the complexity. Isotope exchange reactions play an important role for the stable isotope geochemistry and for the experimental study of sulfur transformations using radiotracers. Microbially catalyzed processes are partly reversible whereby the back-reaction affects our interpretation of radiotracer experiments and provides a mechanism for isotope fractionation. We here review the progress and current status in our understanding of the sulfur cycle in the seabed with respect to its microbial ecology, biogeochemistry, and isotope geochemistry.

Sub‐seafloor biogeochemical processes and microbial life in the Baltic Sea

“…This extrapolated rate matched the upwards methane flux within a factor of two (Jørgensen et al ., ). Since most methanogenesis takes place in the uppermost methane zone where the methane gradient drives methane diffusion up towards the SMT, the close match validates the rate measurements (cf., Flury et al ., ; Jørgensen et al ., ).…”

“…, 40% of the total methane production in the sediment column took place within the SMT. Furthermore, the sulphate flux into the SMT was twice the methane flux due to organoclastic sulphate reduction, in addition to AOM, within the SMT (Jørgensen et al ., ). While sulphate reduction is fed by methane during AOM, organoclastic sulphate reduction uses the diverse fermentation products from the degradation of buried sediment organic matter, just as sulphate reduction does in the main sulphate zone.…”

Butyrate Conversion by Sulfate-Reducing and Methanogenic Communities from Anoxic Sediments of Aarhus Bay, Denmark

“…Where oxygen is depleted, the sediment becomes anoxic. In the anoxic part of the sediment, nitrate, manganese, iron, sulfate, and carbon dioxide, in an order of decreasing energy gain, serve as terminal electron acceptors for the mineralization processes [4,5].…”

Draft Genome Sequence of Desulfofundulus thermobenzoicus subsp. thermosyntrophicus DSM 14055, a Moderately Thermophilic Sulfate Reducer

“…The taxonomic and ecological distribution and genetic diversity of dissimilatory sulfate-reducing microorganisms remain topics of significant interest, with major relevance for understanding biogeochemical cycles (10,11), including the regulation of methanogenesis in sedimentary environments (11)(12)(13). The genome of D. thermobenzoicus is therefore valuable for expanding our understanding of sulfate reducers capable of syntrophic growth with methanogens, as well as for improving the genomic representation of sulfate-reducing Firmicutes.…”