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 11.7 μmol·cm −2 ·kyr −1 . The burial flux of P for the entire CIB (5.7 × 10 6  km 2 ) is 0.01 × 10 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 0.133 μmol·cm −2 ·kyr −1 indicating that the CIB sediments are an important sink for P.