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

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doi: 10.1016/j.gca.2006.01.030
Author(s): Poulton, Simon W.; Canfield, Donald E.
Author Affiliation(s): Primary:
University of Newcastle, School of Civil Engineering and Geosciences, Newcastle upon Tyne, United Kingdom
Other:
University of Southern Denmark, Denmark
Volume Title: Special issue dedicated to Robert A. Berner
Volume Author(s): Canfield, Donald E., prefacer; Lyons, Timothy W.; Morse, John W.
Source: A special issue dedicated to Robert A. Berner, prefaced by Donald E. Canfield, Timothy W. Lyons and John W. Morse. Geochimica et Cosmochimica Acta, 70(23), p.5883-5898. Publisher: Elsevier, New York, NY, International. ISSN: 0016-7037 CODEN: GCACAK
Note: In English. Includes appendices. 95 refs.; illus., incl. 4 tables, sketch map
Summary: 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. Abstract Copyright (2006) Elsevier, B.V.
Year of Publication: 2006
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Chemical composition; Chemical fractionation; Chemical ratios; DSDP Site 598; DSDP Site 599; DSDP Site 600; Deep Sea Drilling Project; Diagenesis; East Pacific; East Pacific Rise; Geochemistry; Hydrothermal conditions; IPOD; Iron; Iron oxides; Leg 92; Marine sediments; Metals; Mid-ocean ridges; Nutrients; Ocean floors; Oxidation; Oxides; Pacific Ocean; Pacific Plate; Paleoenvironment; Phosphorus; Pyrite; Sea water; Sediments; Sulfides
Coordinates: S200000 S180000 W1150000 W1240000
Record ID: 2007106734
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands