URANIUM REMOVAL IN OCEANIC SEDIMENTS AND THE OCEANIC-U BALANCE

Pore water uranium data from the NW Atlantic Ocean, Cariaco Trench, Black Sea and San Clemente Basin are used to calculate fluxes across the sediment-water interface. All samples were collected in situ and show depletions in pore water U relative to the overlying water concentration. The uptake rate of U, derived from pore water gradients, reflects the redox environment, with lowest fluxes (10 μg/cm2ky) in oxic/suboxic sediments of the NW Atlantic dominated by NO3- reduction and higher fluxes (25-70 μg/cm2ky) in the anoxic, sulfate-reducing sediments of the Cariaco Trench, Black Sea and San Clemente Basin. The anoxic fluxes compare well with previous estimates based on solid phase data. Calculations indicate that the areally integrated removal of U into suboxic, hemipelagic sediments is of greater magnitude than that into anoxic, sulfate-reducing sediments. These fluxes are discussed in the context of the oceanic U balance. The removal of U in all oceanic sediments is estimated to account for about 65% of the riverine input, and this sink plus removal of U in altered oceanic crust balances the most probable value for riverine input. © 1990.