HR: 0800h
AN: PP51F-1367    [Abstracts]
TI: Phosphorus and Barium Tracers of Productivity, Nazca Ridge ODP Site 1237, Southeast Pacific Paleoceanographic Transects
AU: * Chun, C O
EM: cchun@ucsc.edu
AF: Ocean Sciences/Institute of Marine Sciences, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Delaney, M L
EM: delaney@ucsc.edu
AF: Ocean Sciences/Institute of Marine Sciences, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
AB: Phosphorus, biogenic barium, and trace metal concentrations have been measured in sediments recovered from Ocean Drilling Program (ODP) Leg 202 Site 1237, Nazca Ridge. Our work has been to understand how these tracers of productivity and sedimentary redox conditions may have responded to the tectonic and climatic evolution of the Southeast Pacific. Changes in lithology as the site moves from a pelagic to hemi-pelagic depositional setting with past plate motion are important when applying paleoproductivity proxies. This unique record extends to 31 Ma over 360 mcd, with a sampling resolution of $\sim$ 0.2 m.y. throughout the sequence. Reactive phosphorus, an indicator of nutrient burial, shows increasing concentrations toward the modern, peaking at 25.3 umol P/g at 15.34 mcd. Biogenic barite, a proxy for export productivity, peaks at 36.90 mcd at a concentration of 3.8 umol Ba/g. Reactive P/Ba excess ratios display lower than expected values for the upper $\sim$ 180 mcd with a sharp increase to higher ratios starting at $\sim$ 270 mcd. Biogenic barite (determined by sequential extraction) defined as Ba barite, were performed on select samples to compare with Ba excess measurements. We found that estimates of biogenic barite from Ba excess are greater than those from barite extraction for these samples. Uranium and manganese enrichment factors (EF) were determined for the entire record. U EF all exceeds crustal values. Dramatic changes in Mn EF at $\sim$ 162 mcd and the observed color change from grayish white to a fairly homogeneous pale brown at this depth lead us to believe that a change in source material, not redox conditions caused this event. We will need an improved age model to generate accumulation rates and to test nutrient burial history at this site.
DE: 4267 Paleoceanography
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1615 Biogeochemical processes (4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting