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Kraal, Peter; Slomp, Caroline P; Forster, Astrid; Kuypers, Marcel MM; Sluijs, Appy (2009): Geochemistry and P and Fe fractionation in anoxic sediments. PANGAEA, https://doi.org/10.1594/PANGAEA.783338, Supplement to: Kraal, P et al. (2009): Pyrite oxidation during sample storage determines phosphorus fractionation in carbonate-poor anoxic sediments. Geochimica et Cosmochimica Acta, 73(11), 3277-3290, https://doi.org/10.1016/j.gca.2009.02.026

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Abstract:
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 CaCO3 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, CaCO3 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.
Coverage:
Median Latitude: 36.278562 * Median Longitude: -92.110596 * South-bound Latitude: 9.265667 * West-bound Longitude: 136.177350 * North-bound Latitude: 87.866580 * East-bound Longitude: -20.047200
Date/Time Start: 1975-03-03T00:00:00 * Date/Time End: 2004-08-27T00:00:00
Minimum DEPTH, sediment/rock: 376.40 m * Maximum DEPTH, sediment/rock: 1135.12 m
Event(s):
41-367 * Latitude: 12.486800 * Longitude: -20.047200 * Date/Time: 1975-03-03T00:00:00 * Elevation: -4748.0 m * Penetration: 1153 m * Recovery: 173.6 m * Location: North Atlantic/BASIN * Campaign: Leg41 * Basis: Glomar Challenger * Method/Device: Drilling/drill rig (DRILL) * Comment: 40 cores; 342 m cored; 0 m drilled; 50.8 % recovery
93-603B * Latitude: 35.495200 * Longitude: -70.028500 * Date/Time: 1983-05-05T00:00:00 * Elevation: -4633.0 m * Penetration: 1576.2 m * Recovery: 485.6 m * Campaign: Leg93 * Basis: Glomar Challenger * Method/Device: Drilling/drill rig (DRILL) * Comment: 74 cores; 674.6 m cored; 0 m drilled; 72 % recovery
207-1260 * Latitude: 9.265667 * Longitude: -54.544033 * Date/Time Start: 2003-02-07T00:00:00 * Date/Time End: 2003-02-12T00:00:00 * Elevation: -2548.8 m * Penetration: 1000.9 m * Recovery: 718.1 m * Location: South Atlantic Ocean * Campaign: Leg207 * Basis: Joides Resolution * Method/Device: Composite Core (COMPCORE) * Comment: 100 cores; 862.2 m cored; 138.7 m drilled; 83.3 % recovery
Parameter(s):
#NameShort NameUnitPrincipal InvestigatorMethod/DeviceComment
1Event labelEvent
2DEPTH, sediment/rockDepth sedmGeocode – mbsf
3Calcium carbonateCaCO3%Kraal, Peter
4Pyrite, FeS2Py%Kraal, PeterEstimates of pyrite content are only given for samples from laminated, reducing intervals.
5Iron/Sulfur ratioFe/SKraal, Peter
6Phosphorus, totalTPµmol/gKraal, Peter
7Phosphorus, exchangeableP exch%Kraal, Peter
8Phosphorus, iron-boundP Fe-bound%Kraal, Peter
9Phosphorus, authigenicP auth%Kraal, Peter
10IronFe%Kraal, Petertotal
11RatioRatioKraal, Petereasily reducible ferric Fe/Fe total
12RatioRatioKraal, Peterpoorly crystalline ferric Fe/Fe total
Size:
1068 data points

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