Distribution and Diagenesis of Phosphorus in the Deep-Sea Sediments of the Central Indian Basin

A regional solid-phase phosphorus (P) speciation study in the Central Indian Basin (CIB) was carried out to elucidate the spatial distribution of sedimentary P species and P diagenesis in an oligotrophic setting. The results show that P enrichment is in the order of biogenic (P-bio)>authigenic (P-auth)>iron bound (P-Fe)>detrital (P-det)>organic (P-org) P. The higher concentrations of P-bio are found in siliceous oozes, which are attributed to high biological productivity in the overlying waters compared to pelagic clay region. High P-auth and P-det contents with low molar C-org/P-react ratios in the pelagic/red clays indicate the deposition of calcium fluorapatite and refractory material from the atmospheric input. The oxygenated bottom water promotes adsorption of P onto iron oxyhydroxides making the P-Fe an important sink. Remobilization of P within the sediments is limited because of well-oxygenated conditions and an efficient adsorption by iron oxyhydroxides and clay-sized sediments. A twofold increase in P-total and P-species is observed in hydrothermally altered, ferruginous sediments from a seamount flank suggesting an important role of hydrothermal processes in P cycling. The calculated P accumulation rate in the present study ranges between 0.6 and 11.7mol cm( -2) kyr(.)( -1) The burial flux of P for the entire CIB (5.7x10(6)km(2)) is 0.01x10(10)mol P per year which accounts for 0.05% of the global flux. The benthic P fluxes from the seawater to the sediments in the area range between 0.0093 and 0.133mol cm( -2) kyr( -1) indicating that the CIB sediments are an important sink for P. Plain Language Summary The paper presents a comprehensive account of regional distribution of pathways of P accumulation in Central Indian Basin, an abyssal region in the Indian Ocean. As mentioned in the Introduction, the papers dealing with P geochemistry in the deep-sea settings are few though these regions occupy a large oceanic space. Thus, our understanding of diagenetic processes and the pathways of P deposition in the oligotrophic areas is not as good as we know about productive continental margins. Lack of significant diagenetic P regeneration, P enrichment in sediments due to hydrothermal alteration, and a significant atmospheric P deposition are the key findings in the paper. The data also show that Central Indian Basin is an important sink for dissolved P. The paper presents quantitative estimates of P accumulation rates and diffusive fluxes of the study area. Extrapolated basinal fluxes are also presented for a global perspective.