INORGANIC GERMANIUM AND SILICA IN THE INDIAN OCEAN: BIOLOGICAL FRACTIONATION DURING (Ge/Si)(OPAL) FORMATION

Hydrographic profiles of inorganic germanium and silica in the western Indian Ocean confirm the silicalike behavior of inorganic germanium in seawater. Combining all existing oceanic data (Indian, Atlantic, Pacific, Bering Sea and Antarctic), these new data provide an improved oceanic Ge to Si relationship: Ge(pM) = 0.699 +/- 0.004 x Si(mu M) + 3.6 +/- 0.4. Simple box models of the ocean demonstrate that the positive Ge intercept in this relationship results from biological fractionation of the Ge/Si ratio: Siliceous organisms discriminate against germanium during production of biogenic opal. This result is confirmed by (Ge/Si)(Opal) analyses of diatoms and radiolaria separated from siliceous oozes of Holocene core tops. A rapid rise in diatom-(Ge/Si)(Opal) recorded in an Antarctic piston core over the interval from the Last Glacial (18 thousand years before present) to the Holocene (present) suggests that biosiliceous productivity was lower and preformed silica concentrations were higher in Southern Ocean surface waters during glacial times.