Benthic cycling of phosphorus in the Eastern Arabian Sea: Evidence of present day phosphogenesis

Results of a study on phosphorus (P) cycling in the Eastern Arabian Sea provides convincing evidence of present-day phosphogenesis in the study area. This finding contrasts with previous reports of the occurrence of only old phosphorites along the Indian margin. Extensive benthic P regeneration is observed in the sediments that are deposited on topographic highs in the western Indian continental margin, which is impinged by a perennial oxygen minimum zone (OMZ). The phosphate flux from the sediments ranged between 1.1 and 22 mmol m− 2 yr− 1. Among the P reservoirs, biogenic P (Pbio) is the major pool of P within the upper 30 cm of sediment. P released from organic matter decomposition and fish debris dissolution mainly controls benthic P regeneration while the role of redox cycling of iron is weak. The change in authigenic P (Pauth) with depth in the sediment and concomitant decrease in porewater dissolved inorganic phosphate (DIP), solid phase Pbio and organic P (Porg) content collectively indicate the transformation of P from labile phases to an authigenic phase. Molar Corg/Porg and Corg/Preactive ratios also support the notion of ongoing phosphogenesis in the area. The content of carbonate fluroapatite (CFA) is elevated especially in one of the three study sites as a result of in-situ precipitation and a contribution from eolian and water column authigenesis. The estimated burial efficiency of P at the sediment-water interface at two locations is only about 2%, which is much less than in the western Arabian Sea also indicating extensive P regeneration.