Phosphorus Accumulation Associated with Intense Diagenetic Metal-Oxide Cycling in Sediments along the Eastern Continental Margin of India

Sequential phosphorus extractions were carried out to understand phosphorus cycling and enrichment in surface sediments along the eastern continental margin of India. Phosphorus associated with authigenic (P_aut) and biogenic (P_bio) phases is high by a factor of 2-10 in the continental shelf sediments compared to slope and deep-sea sediments. Phosphorus associated with Fe oxides (P_Fe) is enriched by a factor of 2-5 in the continental slope and rise sediments (500-3000 m water depth) compared to shelf sediments. Fe-Mn oxy(hydroxides) formed during early diagenesis adsorb phosphate from the water column or pore waters, thereby enriching the P_Fe fraction in the continental slope sediments. These results are in contrast with those from the Arabian Sea, where wide and intense mid-depth oxygen minimum zone (150-1200 m water depth) releases P_Fe to pore waters and enhances P_aut accumulation in the continental slope sediments.