Germanium Isotope Systematics in Marine Systems

保存在硅藻中的海洋锗：硅(Ge：Si)的记录显示了时间的变化，反映了海洋硅循环随时间的变化。这些变化可能是由于(1)蛋白石和非蛋白石相中Ge的相对去除速率，(2)风化和/或热液Ge输入的比率，以及(3)海洋中Si的内部循环和硅藻对Ge/Si的分馏。锗同位素可能有助于限制这些因素的影响。南加州大学的一位科学家计划分析来自大西洋和太平洋的海水，选定分水岭的河水，以及加州边缘和墨西哥湾富铁还原沉积物的沉积物孔隙水，以解决以下问题：(1)海洋盆地内部和海洋盆地之间是否存在Ge同位素变异性？(2)在低温风化过程中是否存在Ge同位素分馏？(3)在沉积物成岩作用期间，Ge同位素是否发生分馏？总体而言，这项研究将确定海洋中无机Ge的源和汇是否以及在哪里存在显著的同位素差异，并应证明这种示踪剂在揭示海洋硅循环及其时间变化的复杂性方面的作用。此外，研究人员计划分析海洋中甲基锗的同位素组成，以评估其同位素组成是否提供了关于其生物地球化学循环的线索。至于更广泛的影响，作为该项目的一部分，将对一名研究生和一名本科生进行培训和支持。

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.