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Extremely high phosphorus concentrations just below the sediment-water interface (SWI) are acheived in anoxic waters by rapid recycling of H2S/SO4 by sulfate reducing bacteria (SRBs) and sulfide oxidizing bacteria (SOBs) accompanied by differences in C/P ratios and efficiencies (S/C ratios) of SRBs and SOBs. :
Phosphorite formation in modern sediments and its implications for phosphogenesis in the NeoProterozoic, First Annual Meeting of the NASA Astrobiology Institue, 1999, (PDF- 0.1Mb)
The Role of Sulphide-oxidizing, Nitrate-reducing Bacteria, Thioploca spp., in Formation of Sedimentary Phosphorites in Peru Margin Sediments, AGU Fall Meeting, 2000, Abstract
The high concentrations of dissolved phosphate result in supersaturation of carbonate-fluorapatite (CFA) in small slice just below the SWI.