We determined the sedimentary concentrations of phosphorus (P), barium (Ba), manganese (Mn), titanium (Ti), aluminum (Al), and uranium (U) for sediment samples from the southeast Pacific Nazca Ridge, Ocean Drilling Program Site 1237. This unique record extends to 31 Ma over 360 meters composite depth (mcd), recording depositional history as the site progressed eastward over its paleohistory. We sampled with a temporal resolution of approximately 0.2 m.y. throughout the sequence, equivalent to an average spacing of 1.63 m/sample. Concentrations of sequentially extracted components of P (oxide-associated, authigenic, organic, and detrital) increase toward the modern. Al/Ti ratios indicate that the background detrital source material is consistent with upper continental crust. U enrichment factors (U (sub EFs) ) generally exceed crustal values and indicate slightly reducing environments. However, authigenic U precipitation can also be influenced by the organic carbon rain rate and may not be solely an indicator of redox conditions. Dramatic changes in MnEFs at approximately 162 mcd, from values between 12 and 93 to values <12 after this depth, and a sharp color contact boundary lead us to believe that a paleoredox boundary from an oxygenated to a more reducing depositional environment occurred near this depth. Estimates of biogenic barite concentrations from a total sediment digestion technique (Ba (sub excess) ) are greater than those from a barite extraction (Ba (sub barite) ) for selected samples across the entire depth range. Applying a range of Ba/Ti ratios from different source materials to correct for detrital inputs does not change the lack of agreement with Babarite concentrations. Reactive P (P (sub reactive) ) concentrations (the sum of oxide-associated, authigenic, and organic P concentrations) increase toward the modern with values typically <12 mu mol P/g from the base of our record through approximately 100 mcd, with a gradual increase to concentrations >15 mu mol P/g. Baexcess follows the same general trends as P (sub reactive) , with concentrations <14 mu mol Ba/g in the lower portion of the record to values >15 mu mol Ba/g. Accumulation rate records of these proxies will be needed to infer paleoproductivity. P (sub reactive) /Ba (sub excess) ratios, an indicator of the relative burial of the nutrient P to organic carbon export, exhibit higher values, similar to modern, from the base of our record through approximately 180 mcd. The remainder of the record exhibits values lower than modern, indicating that organic carbon export to the sediments was higher relative to nutrient burial.

West: -76.2300 East: -76.2300 North: -16.0000 South: -16.0000

Expedition: 202

Site: 202-1237

Provider: SEDIS Publication Catalogue

Data set link: http://sedis.iodp.org/pub-catalogue/index.php?id=10.2973/odp.proc.sr.202.205.2006 (c.f. for more detailed metadata)

Data download: application/pdf

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