The geochemistry of uranium in marine sediments

A fission track technique has been used to determine pore water uranium concentrations on 20 μl samples collected from sediments in the NW Atlantic Ocean, San Clemente Basin and Cariaco Trench. Pore water U profiles in box cores in which suboxic to anoxic diagenesis is occurring show depletions (relative to the overlying water value) and enrichments at depth in the core. The profiles show little consistent relationship to pore water, Fe, Mn or NO₃ profiles. In contrast, pore water U profiles taken by in situ samples (probes, harpoons) show depletions relative to the overlying water value. A comparison of box core and harpoon data for the same station in the San Clemente Basin shows higher pore water U values at depth in the box core than in the in situ samples. We conclude that oxidation of reduced U concentrations and that U can be reduced at pe's comparable to those encountered during Fe and Mn reduction. -from Authors