PII S0016-7037(00)00886-9 Remobilization of authigenic uranium in marine sediments by bioturbation

• Main Authors: Alexander Van Geen, Martin Q. Fleisher
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2000
• Subjects: Pacific; Northwest Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.541.4387; http://www.ldeo.columbia.edu/~avangeen/pdf/Zheng_GCAU1_02.pdf

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/cm2 kyr) to high (2.8 g/cm2 kyr) OCF to the sediments. BWO concentrations vary substantially among the sites, ranging from 3 to 270 M. 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 (15 M). 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 © 2002 Elsevier Science Ltd 1.