In this study the response of sedimentary phosphorus (P) burial to changes in primary productivity and bottom water oxygen concentrations during the Late Quaternary is investigated, using two sediment cores from the Arabian Sea, one recovered from the continental slope and the other from the deep basin. The average solid-phase P speciation in both cores is similar, authigenic and biogenic ( fish debris) apatite make up the bulk of the P inventory (ca. 70％); whereas P adsorbed to iron oxides, organic P, and detrital apatite constitute minor fractions. Postdepositional redistribution has not significantly altered the downcore distribution of total solid-phase P. Phosphorus burial efficiencies are generally lower during periods of increased paleoproductivity. This is caused by (a) partial decoupling of the P export flux, consisting primarily of particulate organic P, and the P burial flux, consisting primarily of biogenic and authigenic apatite; and (b) the lack of increased rates of authigenic CFA formation during periods of higher P deposition. In addition, fluctuations in bottom water oxygen concentrations may have affected P burial in continental slope sediments. The results of this study indicate that higher primary productivity induces more efficient P cycling. On time scales exceeding the oceanic P residence time, this process may induce higher surface water productivity, thus creating a positive feedback loop. In the Arabian Sea, this feedback mechanism may have contributed to changes in sea surface productivity on sub-Milankovitch time scales because P, regenerated on the continental slopes of the Oman and Somalian coastal upwelling zones, is reintroduced into the photic zone relatively fast.』
2. Material and methods
2.1. Sample locations
2.2. Solid-phase analysis
3. Results and discussion
3.1. Burial of total solid-phase P
3.2. Sedimentary P speciation
3.2.1. Organic phosphorus
3.2.2. Biogenic apatite
3.2.3. Detrital and iron bound P
3.2.4. Authigenic apatite
3.3. Cause and implications of reduced PBE during periods of high productivity
|Reactive P sinks||Continental margin1||Pacific Ocean2||Arabian Sea3||Estimated global average|
|Froelich (1982)||Ruttenberg (1993)||This study|
Note that the P speciation (organic P, iron bound P, and biogenic
authigenic P fractions) in deep Pacific Ocean and Arabian Sea
sediments is similar. The global average for the reactive P partitioning
in marine sediments was estimated using the results for the continental
margin (Ruttenberg, 1993; second column) and the Arabian Sea
(deep-pelagic sediment; fourth column), assuming that the total
annual sedimentary burial of reactive P in deep pelagic sediments
is of the same magnitude as that in continental shelf areas (Froelich,
1984; Follmi, 1996). The P fraction associated with biogenic
apatite for continental margin sediments is assumed to constitute
half the authigenic P pool (likewise Arabian Sea sediments).
Comparison with previous estimates (Froelich et al., 1982; Ruttenberg
and Berner, 1993) indicates that burial of authigenic and biogenic
apatite fraction is relatively more important than previously
assumed, whereas organic P burial is of secondary importance.
1 Ruttenberg (1993).
2 Filippelli and Delaney (1996).
3 Average from NIOP455 and NIOP487.
4 Primarily consisting of P associated with biogenic apatite (fish debris).