Journal article
Pyrite oxidation during sample storage determines phosphorus fractionation in carbonate-poor anoxic sediments
Geochimica et Cosmochimica Acta, Vol.73(11), pp.3277-3290
2009
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Abstract
<p>We investigated the phosphorus (P) and iron (Fe) fractionation in four cores with anoxic sediments, deposited during the mid-Cretaceous oceanic anoxic event 2 (∼94 Ma) and the Paleocene–Eocene thermal maximum (∼55 Ma), that were exposed to oxygen after core recovery. Surprisingly, P associated with iron oxyhydroxides (Fe-bound P) was a major P phase in these laminated sediments deposited under euxinic conditions. A significant fraction of total Fe was present as (poorly) crystalline ferric Fe. This fraction increased with increasing storage time of the investigated cores. In carbonate-poor samples, Fe-bound P accounted for up to 99% of total P and its abundance correlated with pyrite contents. In samples with higher CaCO<sub>3</sub> contents (>5 wt% in the investigated samples), P was mostly present in authigenic Ca–P minerals, irrespective of pyrite contents. We conclude that the P fractionation in anoxic, carbonate-poor, sediments is strongly affected by pyrite oxidation that occurs when these sediments are exposed to oxygen. Pyrite oxidation produces sulfuric acid and iron oxyhydroxides. The abundance of poorly crystalline Fe oxyhydroxides provides further evidence that these were indeed formed through recent (post-recovery) oxidation rather than in situ tens of millions of years ago. The acid dissolves apatite and the released phosphate is subsequently bound in the freshly formed iron oxyhydroxides. Pyrite oxidation thus leads to a conversion of authigenic Ca–P to Fe-bound P. In more calcareous samples, CaCO<sub>3</sub> can act as an effective buffer against acidic dissolution of Ca–P minerals. The results indicate that shielding of sediments from atmospheric oxygen is vital to preserve the in situ P fractionation and to enable a valid reconstruction of marine phosphorus cycling based on sediment records.</p>
Details
- Title
- Pyrite oxidation during sample storage determines phosphorus fractionation in carbonate-poor anoxic sediments
- Creators
- Peter Kraal - Southern Cross UniversityCaroline P Slomp - Utrecht UniversityAstrid Forster - Royal Netherlands Institute for Sea ResearchMarcel MM Kuypers - Max Planck Institute for Marine MicrobiologyAppy Sluijs - Utrecht University
- Publication Details
- Geochimica et Cosmochimica Acta, Vol.73(11), pp.3277-3290
- Identifiers
- 1159; 991012820618202368
- Academic Unit
- Southern Cross GeoScience
- Resource Type
- Journal article