Germanium Isotope Systematics in Marine Systems

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Records of oceanic germanium:silicon (Ge:Si) preserved in diatoms show temporal variations that reflect changes in the marine Si cycle over time. These variations may be due to (1) the relative rates of Ge removal in opal and non-opal phases, (2) the ratio of weathering and/or hydrothermal Ge inputs, and (3) the internal cycling of Si in the ocean and Ge/Si fractionation by diatoms. Germanium isotopes may help constrain the influences of these factors. A scientist for the University of Southern California plans to analyze seawater from the Atlantic and Pacific Ocean, river water from selected watersheds, and sediment pore waters from iron-rich reducing sediments in the California Margin and Gulf of Mexico to address the following questions: (1) Does Ge isotope variability exist within and between ocean basins?; (2) Is there Ge isotope fractionation during low-temperature weathering?; and (3) Are Ge isotopes fractionated during sediment diagenesis? Overall, this study will determine if and where significant isotopic differences exist in the sources and sinks for inorganic Ge in the oceans and should document the utility of this tracer for unraveling the complexities of the marine Si cycle and its temporal variation. In addition, the researcher plans to analyze the isotopic composition of methyl germanium in the oceans to evaluate if its isotopic composition provides clues about its biogeochemical cycling.As regards broader impacts, one graduate and one undergraduate student would be trained and supported as part of this project.