『Abstract
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.』
1. Introduction
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
4. Conclusions
Acknowledgments
References
Reactive P sinks | Continental margin1 | Pacific Ocean2 | Arabian Sea3 | Estimated global average | ||
Froelich (1982) | Ruttenberg (1993) | This study | ||||
Organic P | 22% | 6% | 10% | 40% | 22% | 16% |
Iron-P | 16% | 11% | 12% | 11% | 22% | 14% |
Loosely sorbed-P | 7% | 5% |
|
− | 7% |
|
Carbonate-P |
|
|
40% |
|
||
Fish-P | <2% | |||||
Authigenic-P | 38% | <10% | 34.5% | |||
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). |