This is an "Accomplishment-Based Renewal" to continue work measuring germanium/silicon ratios in marine biogenic silica to characterize variations in the oceanic silica and germanium cycles. Over the next three years detailed (Ge/Si) Opal records will be produced for two time scales: Late Pleistocene piston cores (0 - 450 Kyr B.P.), and Late Paleogene to Neogene Ocean Drilling Project Sites (0 - 40 Myr B.P.). These diatom Ge/Si data, when combined with biogenic opal, carbonate, and organic carbon accumulation rates plus diatom preservation indices in the same cores, will permit features of past global oceanic silica and germanium cycles to be reconstructed including (1) changes in global input and removal via mid-ocean ridge hot springs, continental rivers, conversion of organogermanium, and burial of biogenic opal; (2) changes in local versus global siliceous accumulation rates; and (3) variations in local biosiliceous productivity and preformed silica concentrations of high latitude surface waters. Ancillary work will include (1) continuing determinations of Ge and Si associated with hydrothermal effluents and plumes (southern EPR, Juan de Fuca), (2) finishing determinations of inorganic and methylated germanium in the Black Sea, (3) starting diatom cultures and dissolution experiments to directly measure Ge/Si-biofractionation factors and to assess the effect of diatom species' preservation on the burial ratio, and (4) constructing time-dependent models of the germanium and silicon cycles to complement information derived from the traditional carbonate paleotracers ( 180, 13C, Cd/Ca, Li/Ca, Sr/Ca, 87Sr/86Sr) for areas and times where carbonates are not preserved and for oceanic processes whose systematics are not recorded by calcareous microfossils.
