HR: 0800h
AN: PP11A-0242    [Abstracts]
TI: Sedimentary Trace Metal-Organic Interactions as Proxies for Oceanic Redox Conditions
AU: * Cruse, A M
EM: anna.cruse@okstate.edu
AF: Oklahoma State University, School of Geology 105 Noble Research Center, Stillwater, OK 74078-3031, United States
AU: Lyons, T W
EM: timothy.lyons@ucr.edu
AF: University of California, Department of Earth Sciences, Riverside, CA 92521-0423, United States
AU: Hannigan, R
EM: hannigan@astate.edu
AF: Arkansas State University, Department of Chemistry, State University, AR 72401, United States
AB: Knowledge of trace-metal partitioning in oceanic sediments (e.g., Fe, Mo, U, Zn) are requisite to the construction of accurate models of geochemical cycling in modern and ancient waters. Factors such as oxygen penetration depth and bottom-water redox; sedimentation rate; and supply of reactants, such as dissolved sulfide, are known to affect metal sequestration in and remobilization from coastal sediments. In addition to these factors, the flux of organic carbon (OC) and the composition of this carbon are also a key in the sequestration of these metals. Currently, however, there is an absence of quantitative information on the mass balance of metals fixed in coastal sediments through direct interactions with OC, how OC remineralization affects this mass balance, and the specific nature of the metal-OC relationship. To address these issues, we have undertaken a field-based study to test the hypothesis that porewater redox conditions are recorded in the concentrations of trace metals bound in the sedimentary OC pool. We have collected sediments from several modern anoxic/euxinic basins: the central Black Sea, the Orca Basin, the Cariaco Basin, and Effingham Inlet (Vancouver Island). These environments vary in terms of dissolved sulfide concentrations and sedimentary iron sulfide geochemistry. Additionally, the sediments are characterized by a range in OC concentrations, and proximity to terrestrial sources. Extractable organic carbon was characterized with gas chromatography, and OC-bound metals are quantified using high-performance liquid chromatography- inductively coupled mass spectrometry. The preliminary results suggest that variations in the ratios of aromatic to saturate hydrocarbons may control the speciation of metals in the organic carbon pool. Bottomwater redox may be one factor controlling this relationship, although it is currently unclear if this is due to variations in metal speciation or the direct involvement of S in the OC-metal reaction mechanism. The results of our analyses will be used to construct an integrated mass balance for metal sequestration-OC reactions during diagenesis. Beyond paleoceanographic reconstructions, our quantitative models for trace metal-OC interactions in modern sediments are critical to address modern environmental concerns, such as trace metal pollution in response to anthropogenic eutrophication and predictions of chemical responses to global warming.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0460 Marine systems (4800)
DE: 0461 Metals
DE: 1055 Organic and biogenic geochemistry
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting