Abstract
Core sediment samples were collected from the middle shelf of the East China Sea (ECS) to study the phosphorus forms, P accumulation rate (PAR), P burial efficiency and the burial flux in the ECS. The sediment samples were sequentially extracted and directly extracted to analyze different forms of sedimentary P: lossely sorbed P and iron-bound P (P CDB); inorganic P associated with francolite (carbonate fluorapatite, CFA), biogenic hydroxyapatite, smecite, and CaCO 3 (P CFA); detrital P (P Detrital); organic P (P Organic); and total P. In addition, the Fe contents in the citrate-dithionite-bicarbonate (CDB) extracted solution were also measured. The total concentrations of P in the surface sediments in the study area ranged from 13.5 to 22.3 μmol g −1. Inorganic P was the major form and accounted for 72–93% of the total P pool. The average percentage of each fraction of P followed the sequence: P Detrital (70%)>P Organic (15.5%)>P CDB (8.4%)>P CFA (5.8%). The distribution pattern of total P in the surface sediment was similar to that of P Detrital and P Organic, but different from that of P CDB and P CFA. The profile variation of P Organic was the most significant among the phosphorus forms at the study stations. The concentrations of P CDB and P CFA showed minor variation with depth. These results may suggest that transformations of P Organic, P CFA and P CDB occurred at the study stations during sedimentary P burial. Based on the concentrations of total P, P CDB and Fe CDB obtained in the present study and the mass accumulation rate (MAR) reported in the literature, the values of the PAR, the P diffusion flux ( J PFe) supplied by reducible iron hydroxides and the P burial efficiency were calculated. The calculated results for PAR and J PFe in the study area ranged from 1.02 to 24.23 μmol cm −2 yr −1 and from 0.1 to 2.11 μmol cm −2 yr −1, respectively. The phosphorus burial efficiency (PBE) was approximately 90%. The ECS is a phosphorus sink, and the average annual P burial flux has been reasonably estimated to be in the range of 20–25×10 9 mol yr −1.
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