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

• Published in: Journal of geophysical research. Oceans 2018-11, Vol.123 (11), p.7963-7982
• Main Authors: Linsy, P., Nagender Nath, B., Mascarenhas‐Pereira, M. B. L., Chauhan, Teena, Sebastian, Tyson, Babu, C. P., Kurian, Siby, Miriyala, Pavan, Kazip, Armoury, Borole, D. V., Khadge, N. H.
• Format: Article
• Language: English
• Subjects: Abyssal zone; Accumulation; Adsorption; Benthos; Bottom water; Calcium; Clay; Continental margins; Deep sea sediments; Deposition; Diagenesis; Distribution; Fluorapatite; Fluxes; Geochemistry; Geophysics; Hydrothermal activity; Hydrothermal alteration; Iron; Iron and steel making; Oozes; Oxygenation; Pelagic clay; Phosphorus; Ratios; Regeneration; Regeneration (biological); Seamounts; Seawater; Sediment; Sediments; Spatial distribution; Speciation
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2018JC014386

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 (Pbio) > authigenic (Pauth) > iron bound (PFe) > detrital (Pdet) > organic (Porg) P. The higher concentrations of Pbio are found in siliceous oozes, which are attributed to high biological productivity in the overlying waters compared to pelagic clay region. High Pauth and Pdet contents with low molar Corg/Preact 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 PFe 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 Ptotal 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 × 106 km2) is 0.01 × 1010 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. 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. Extrapolat