Remobilization of authigenic uranium in marine sediments by bioturbation

Publication Type  Journal Article
Year of Publication  2002
Authors  Zheng, Y.; Anderson, R. F.; Van Geen, A.; Fleisher, M. Q.
Journal Title  Geochimica Et Cosmochimica Acta
Volume  66
Issue  10
Pages  1759-1772
Journal Date  May
ISBN Number  0016-7037
Accession Number  ISI:000175577200006
Key Words  santa-barbara basin; saanich inlet sediments; pore-water; black-sea; early diagenesis; trace-metals; monica basin; reduction; california; particulate
Abstract  

Uranium behaves as a nearly conservative element in oxygenated seawater, but it is precipitated under chemically reducing conditions that occur in sediments underlying low-oxygen bottom water or in sediments receiving high fluxes of particulate organic carbon. Sites characterized by a range of bottom-water oxygen (BWO) and organic carbon flux (OCF) were studied to better understand the conditions that determine formation and preservation of authigenic U in marine sediments. Our study areas are located in the mid latitudes of the northeast Pacific and the northwest Atlantic Oceans, and all sites receive moderate (0.5 g/cm(2) kyr) to high (2.8 g/cm(2) kyr) OCF to the sediments. BWO concentrations vary substantially among the sites, ranging from <3 to similar to270 muM. A mass balance approach was used to evaluate authigenic U remobilization at each site. Within each region studied, the supply of particulate nonlithogenic U associated with sinking particles was evaluated by means of sediment traps. The diffusive flux of U into sediments was calculated from pore-water U concentration profiles. These combined sources were compared with the burial rate of authigenic U to assess the efficiency of its preservation. A large fraction (one-third to two-thirds) of the authigenic U precipitated in these sediments via diffusion supply is later regenerated, even under very low BWO concentrations (similar to15 muM). Bioturbating organisms periodically mix authigenic U-containing sediment upward toward the sediment-water interface, where more oxidizing conditions lead to the remobilization of authigenic U and its loss to bottom waters. Copyright (C) 2002 Elsevier Science Ltd.

Notes  

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URL  <Go to ISI>://000175577200006
DOI  Pii S0016-7037(00)00886-9