LATE CENOZOIC Ge/Si RECORD OF MARINE BIOGENIC OPAL: IMPLICATIONS FOR VARIATIONS OF RIVERINE FLUXES TO THE OCEAN

We have determined germanium/silicon ratios in purified diatoms and radiolarians from siliceous sediments in Holocene core tops, one late Pleistocene piston core, and four high-latitude Southern Ocean Deep Sea Drilling Project (DSDP) sites ranging in age from Holocene to Oligocene. High-latitude Holocene diatoms in the 10- to 38-mu m size fraction ([Ge/Si](opal) = 0.693 +/- 0.039 x 10(-6)) faithfully record the present oceanic ratio ([Ge/Si](seawater) = 0.699 +/- 0.004 x 10(-6)) This confirms that diatoms from siliceous oozes are monitors of seawater Ge/Si and may record past changes in rates of delivery of weathering products to the sea from continental and seafloor weathering. Large diatoms and radiolarians display ratios much lower than (Ge/Si)(seawater), suggesting that (Ge/Si)(opal), to some extend, displays the effects of biological fractionation. From 0 to 2.5 m.y.B.P., (Ge/Si)(opa)l in diatoms from DSDP sites ranges from about 0.54 to 0.70 x 10(-6), similar to the range observend in one late Pleistocene piston core over the last 25 kyr. From 2.5 to 6 m.y.B.P., the ratio is more variable, while prior to 10 m.y.B.P., ratios are clearly