Work Package 5

Bacterial sulfide oxidation in the water column and in sediments and the link to the phosphorus cycle

Involved Scientists


The Benguela upwelling system is one of the very few open ocean environments where higher concentrations of sulfide frequently occur in the water column concurrent with blooms of sulfide oxidizing bacteria (Lavik et al., 2009). The surface sediments can contain extremely high sulfide concentrations, and are densely populated by large sulfide oxidizing bacteria, which have been shown to be involved in the formation of phosphorite (Schulz & Schulz, 2005), a major sink for phosphorus. At present, it is not clear under which environmental conditions sulfide oxidizing bacteria will cease to be able to efficiently detoxify sulfide. A build up of sulfide may trigger bacterial phosphate release and concurrent phosphogenesis, as observed in laboratory studies (Brock & Schulz-Vogt, 2011) and suggested by the occurrence of phosphorus rich deposits in areas of frequent sulfide eruptions (Compton & Bergh, 2016).

General Questions and Research topics:

  • Under which environmental conditions can we expect sulfide accumulation in the open water and how will this affect phosphorus cycling?

During the research expeditions, this study will initially provide a detailed description of the in situ distribution of gases, nutrients and trace metals together with bacterial distribution, content of polyphosphate, gene expression patterns and fluxes across the sediment/water interface. These parameters will be determined both in the water column and in the sediment following a transect with changing bottom water redox conditions. Subsequently, the potential for sulfide oxidation under in situ conditions will be determined by following the concentration of sulfide over time after a small sulfide addition. The availability of oxygen and nitrate will then be continuously lowered to determine tipping points with critically low sulfide oxidation rates. Finally, representative samples will be long-term incubated under varying availability of oxygen and nitrate and the effects on the potential for sulfide oxidation will be monitored. Parallel experiments will address the effect of sulfide on bacterial phosphate release to determine which levels of sulfide have critical effects on phosphorus cycling and thereby the potential to change the overall carbon budget. These experiments will provide the boundary conditions for modeling the effects of variations in physical forcing on the build up of sulfide, which has severe consequences for the budgets of oxygen and carbon.