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| Titel |
Sedimentary phosphorus and iron cycling in and below the oxygen minimum zone of the northern Arabian Sea |
| VerfasserIn |
P. Kraal, C. P. Slomp, D. C. Reed, G.-J. Reichart, S. W. Poulton |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 7 ; Nr. 9, no. 7 (2012-07-16), S.2603-2624 |
| Datensatznummer |
250007188
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| Publikation (Nr.) |
 copernicus.org/bg-9-2603-2012.pdf |
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| Zusammenfassung |
| In this study, we investigate phosphorus (P) and iron (Fe) cycling in
sediments along a depth transect from within to well below the oxygen
minimum zone (OMZ) in the northern Arabian Sea (Murray Ridge). Pore-water
and solid-phase analyses show that authigenic formation of calcium phosphate
minerals (Ca-P) is largely restricted to where the OMZ intersects the
seafloor topography, likely due to higher depositional fluxes of reactive P. Nonetheless, increased ratios of organic carbon to organic P
(Corg/Porg) and to total reactive P (Corg/Preactive) in
surface sediments indicate that the overall burial efficiency of P relative
to Corg decreases under the low bottom water oxygen concentrations
(BWO) in the OMZ. The relatively constant Fe/Al ratio in surface sediments
along the depth transect suggest that corresponding changes in Fe burial are
limited. Sedimentary pyrite contents are low throughout the ~25 cm
sediment cores at most stations, as commonly observed in the Arabian Sea
OMZ. However, pyrite is an important sink for reactive Fe at one station in
the OMZ. A reactive transport model (RTM) was applied to quantitatively
investigate P and Fe diagenesis at an intermediate station at the lower
boundary of the OMZ (bottom water O2: ~14 μmol L−1).
The RTM results contrast with earlier findings in showing that Fe redox
cycling can control authigenic apatite formation and P burial in Arabian Sea
sediment. In addition, results suggest that a large fraction of the
sedimentary Ca-P is not authigenic, but is instead deposited from the water
column and buried. Dust is likely a major source of this Ca-P. Inclusion of
the unreactive Ca-P pool in the Corg/P ratio leads to an overestimation
of the burial efficiency of reactive P relative to Corg along the depth
transect. Moreover, the unreactive Ca-P accounts for ~85% of
total Ca-P burial. In general, our results reveal large differences in P and
Fe chemistry between stations in the OMZ, indicating dynamic sedimentary
conditions under these oxygen-depleted waters. |
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