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Poulton, Simon W; Canfield, Donald E (2006): Iron and phosphorus speciations in DSDP Leg 92 sediments. PANGAEA,, Supplement to: Poulton, SW; Canfield, DE (2006): Co-diagenesis of iron and phosphorus in hydrothermal sediments from the southern East Pacific Rise; implications for the evaluation of paleo-sea water phosphate concentrations. Geochimica et Cosmochimica Acta, 70(23), 5883-5898,

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We present a detailed study of the co-diagenesis of Fe and P in hydrothermal plume fallout sediments from ~19°S on the southern East Pacific Rise. Three distal sediment cores from 340-1130 km from the ridge crest, collected during DSDP Leg 92, were analysed for solid phase Fe and P associations using sequential chemical extraction techniques. The sediments at all sites are enriched in hydrothermal Fe (oxyhydr)oxides, but during diagenesis a large proportion of the primary ferrihydrite precipitates are transformed to the more stable mineral form of goethite and to a lesser extent to clay minerals, resulting in the release to solution of scavenged P. However, a significant proportion of this P is retained within the sediment, by incorporation into secondary goethite, by precipitation as authigenic apatite, and by readsorption to Fe (oxyhydr)oxides. Molar P/Fe ratios for these sediments are significantly lower than those measured in plume particles from more northern localities along the southern East Pacific Rise, and show a distinct downcore decrease to a depth of ~12 m. Molar P/Fe ratios are then relatively constant to a depth of ~35 m. The Fe and P speciation data indicate that diagenetic modification of the sediments is largely complete by a depth of 2.5 m, and thus depth trends in molar P/Fe ratios can not solely be explained by losses of P from the sediment by diffusion to the overlying water column during early diagenesis. Instead, these sediments are likely recording changes in dissolved P concentrations off the SEPR, possibly as a result of redistribution of nutrients in response to changes in oceanic circulation over the last 10 million years. Furthermore, the relatively low molar P/Fe ratios observed throughout these sediments are not necessarily solely due to losses of scavenged P by diffusion to the overlying water column during diagenesis, but may also reflect post-depositional oxidation of pyrite originating from the volatile-rich vents of the southern East Pacific Rise. This study suggests that the molar P/Fe ratio of oxic Fe-rich sediments may serve as a proxy of relative changes in paleoseawater phosphate concentrations, particularly if Fe sulfide minerals are not an important component during transport and deposition.
Median Latitude: -19.128400 * Median Longitude: -120.465867 * South-bound Latitude: -19.451500 * West-bound Longitude: -124.676800 * North-bound Latitude: -18.929000 * East-bound Longitude: -116.839500
Date/Time Start: 1983-03-17T00:00:00 * Date/Time End: 1983-03-23T00:00:00
92-598 * Latitude: -19.004700 * Longitude: -124.676800 * Date/Time: 1983-03-17T00:00:00 * Elevation: -3699.0 m * Penetration: 52.4 m * Recovery: 41.2 m * Location: South Pacific * Campaign: Leg92 * Basis: Glomar Challenger * Device: Drilling/drill rig (DRILL) * Comment: 8 cores; 52.4 m cored; 0 m drilled; 78.7 % recovery
92-599 * Latitude: -19.451500 * Longitude: -119.881300 * Date/Time: 1983-03-20T00:00:00 * Elevation: -3654.0 m * Penetration: 46.3 m * Recovery: 34.8 m * Location: South Pacific/PLATEAU * Campaign: Leg92 * Basis: Glomar Challenger * Device: Drilling/drill rig (DRILL) * Comment: 5 cores; 46.3 m cored; 0 m drilled; 75.1 % recovery
92-600 * Latitude: -18.929000 * Longitude: -116.839500 * Date/Time: 1983-03-23T00:00:00 * Elevation: -3346.0 m * Penetration: 10.4 m * Recovery: 5.4 m * Location: South Pacific/PLATEAU * Campaign: Leg92 * Basis: Glomar Challenger * Device: Drilling/drill rig (DRILL) * Comment: 1 cores; 5.4 m cored; 5 m drilled; 99.6 % recovery
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