| One of the fundamental tasks of chemical oceanographers is to understand how elements cycle in the ocean. Rather than achieving an equilibrium controlled concentration level in the ocean, balance between removal of elements and inputs often determines the abundance of the elements in sea water.; Removal of germanium (Ge) by biogenic opal sedimentation is a well known process. However, a large non-opal sink (8.6 x 106 mole/yr) of Ge must exist to balance the most reasonable hydrothermal and riverine input fluxes of Ge. Analyses of Ge and silicon (Si) in clay size fraction sediments from the South Atlantic Ocean yielded a Ge/Si ratio of ∼4.65 x 10-6 (mole/mole), much higher than in probable source material of 2 x 10-6, indicating a hydrogenous clay Ge sink.; Enrichment of molybdenum (Mo) in anoxic marine basins sediments is thought to be related to authigenic Mo-sulfide formation. Measurements of pore water and sediment Mo concentrations, together with pore water sulfide concentrations, in a suite of multi-cores in the Santa Barbara Basin indicate that there are two threshold levels of sulfide for authigenic Mo formation. A sulfide concentration of ∼0.1 muM appears to be important for Mo, possibly Mo-Fe-sulfide, precipitation. A second threshold value of ∼100 muM appears to be important for Mo-sulfide precipitation.; Enrichment of uranium (U) is observed in both anoxic and suboxic marine sediments. Multiple sites in the mid-latitudes of marginal seas of the northeast Pacific and the northwest Atlantic Oceans were used to understand factors responsible for formation of authigenic U in marine sediment, as well as the conditions that determine whether authigenic U will be buried. Although the major source of authigenic U to the sites is via diffusion, particulate non-lithogenic U formed in surface waters is found to be important in places such as Santa Barbara Basin and Saanich Inlet. Uranium is reduced and precipitated primarily in the zone of Fe reduction, possibly through microbially mediated reactions. A large fraction of authigenic U formed in the bioturbed sediments is regenerated and returned to water column. |
