Trace metal signatures in continental sedimentary systems: Isotope constraints, biogeochemistry, and potential as a paleoclimatic tracer

智力上的优点。拟议的工作将解决有关的地球化学相互作用，导致去除钼，铀和钒从水生系统和分馏的钼同位素发生在有机物分解的假设。我们的研究地点，坦噶尼喀湖，是一个古老的裂谷湖，具有含氧的上层水柱和硫化物的深层沃茨。这两个沃茨下沉积物的存在提供了一个令人兴奋和及时的机会，以量化金属溶解度的变化，并测试与金属沉淀有关的同位素分馏预测。我们的工作是由两个假设，预测金属积累速率和碳循环之间的紧密联系。这些假说预测不同行为的钼同位素取决于上覆水是否有硫化物的存在。(1)在上覆水体不含硫化物的地区，我们推测沉积物中微量元素的积累和Mo同位素组成与有机碳的循环密切相关。(2)在沉积物沐浴与硫化物丰富的水，我们假设，微量元素富集仍然敏感的有机碳循环，但钼同位素值不变。虽然我们使用这些假设作为我们研究的指导，但我们确实期望目标元素对有机碳循环和水柱硫化物浓度表现出各种各样的敏感性。目标元素已经提供了潜在的地球化学示踪剂，这一建议是一个令人兴奋的机会，解决重要的问题，他们的环境化学。钼同位素也保留潜力作为示踪剂的可用性的氧和硫化物通过地质时期，这一建议将使我们能够检查水柱硫化物的存在如何影响钼同位素的行为。最后，非洲五大湖拥有丰富的气候历史记录，可以追溯到中新世。我们在这里提供的是一个机会来校准一套沉积示踪剂，最终可以提供强大的见解对地球化学过程，不仅在坦噶尼喀，但在其他沉积系统以及。坦噶尼喀湖是东非人民的宝贵资源。这个湖包含了地球上很大一部分的淡水，并为几个国家的经济提供了宝贵的渔业资源。从广义上讲，这一提议为解决湖泊的碳动态如何应对过去气候变化的问题提供了工具。作为这项建议的一部分，McManus将在2006年夏天参加Nyanza项目。该尼扬扎项目是一个本科生/研究生实地研究计划，提供了机会，研究古气候学和地质学在大陆裂谷摇篮之一，世界上最古老的湖泊。作为该项目的参与者，麦克马纳斯将参与培训美国和非洲学生，我们计划让一名非洲学生和两名美国学生参与我们的实地研究。我们还将在资助的第二年支持俄勒冈州立大学的本科生。本科生对PI的研究计划做出了重大贡献，导致在主要会议上发表的摘要，大学范围内的学生研究计划，以及两份手稿的合著。我们学院开始让我们大学荣誉学院的学生参与研究，我们计划在近期启动一个REU项目。我们期望有一个学生从这些计划之一参与拟议的研究以及。最后，该提案将为博士后研究助理（Chris Siebert）提供支持。

Intellectual merit. The proposed work will address hypotheses regarding thebiogeochemical interactions that lead to the removal of molybdenum, uranium, andvanadium from aquatic systems and the fractionation of Mo isotopes that occurs duringorganic matter decomposition. Our study site, Lake Tanganyika, is an ancient rift lake thathas an oxygenated upper water column and sulfidic deep waters. The existence ofsedimentary deposits underlying both these waters offers an exciting and timely opportunityto quantify changes in metal solubility and to test predictions regarding isotope fractionationassociated with metal precipitation. Our work is guided by two hypotheses that predict aclose link between metal accumulation rate and carbon cycling. These hypotheses predictdifferent behavior for Mo isotopes depending on whether or not the overlying water hassulfide present. (1) In regions where the overlying water column is absent of sulfide, wehypothesize that trace element accumulation in the sediments and Mo isotope compositionsare closely coupled to the cycling of organic carbon. (2) Where sediments are bathed withsulfide-rich water, we hypothesize that trace element enrichments remain sensitive to theorganic carbon cycling but Mo isotope values are invariant. Although we use thesehypotheses as a guide for our research, we do expect that the targeted elements will exhibit arange of sensitivities to organic carbon cycling and water column sulfide concentrations.Broader impacts I: Scientific value. The targeted elements already offer potential asbiogeochemical tracers, and this proposal represents an exciting opportunity to addressimportant issues regarding their environmental chemistry. Molybdenum isotopes alsoretain potential as a tracer for the availability of oxygen and sulfide through geologic time,and this proposal will allow us to examine how the presence of water column sulfideinfluences Mo isotope behavior. Finally, the African Great Lakes harbor rich records ofclimate history extending back to the Miocene. What we offer here is an opportunity tocalibrate a suite of sedimentary tracers that could ultimately provide powerful insights onbiogeochemical process, not only in Tanganyika, but in other sedimentary systems as well.Broader impacts II: Human impacts and opportunities for education. LakeTanganyika is a valuable resource to the East African people. The lake contains asignificant fraction of the Earth's fresh water and supplies the economies of several nationswith a valuable fisheries resource. In a broad sense, this proposal offers tools foraddressing questions related to how the lake's carbon dynamics have responded to pastchanges in climate. As part of this proposal, McManus will be participating in the Nyanzaproject during the summer of 2006. The Nyanza Project is an undergraduate/graduate fieldresearch program that offers opportunities to study paleoclimatology and geology in acontinental rift cradling one of the world's oldest lakes. As a participant in the programMcManus will be engaged in training both U.S. and African students, and we plan onhaving one African student and two U.S. students working on our field research. We willalso support an OSU undergraduate during our second year of funding. Undergraduatestudents have contributed significantly to the PI's research program resulting in abstractsdelivered at major conferences, university-wide student research programs, and coauthorshipon two manuscripts. Our college is beginning to engage students from our university'shonors college in research and we are planning on initiating an REU program in the nearterm. We anticipate having a student from one of these programs participating in theproposed research as well. Finally, this proposal will provide support for a postdoctoralresearch associate (Chris Siebert).